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					                                       Network Design – Draft




                                 DfES
                        Network Services Project

                         Network Design

                                      Draft v3.1


     Copyright © 2004 The JNT Association UKERNA manages the networking
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     copyright preserved. The reproduction of logos without permission is expressly forbidden.
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                   © The JNT Association 2004        NDD/ NSP/RS/ND




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                                           Network Design

1    Purpose................................................................................................................. 4
     1.1    Scope ......................................................................................................... 4
     1.2    Target Audience ....................................................................................... 5
     1.3    Strategic Issues ........................................................................................ 5
     1.4    Summary of Responsibilities .................................................................. 6
     1.5    National Education Network ................................................................... 8
     1.6    Interoperability and Standards ............................................................... 8
2    Network Design .................................................................................................. 9
     2.1    Transmission Technologies .................................................................... 9
     2.2    IP Addressing.......................................................................................... 15
     2.3    Network Address Translation ............................................................... 17
     2.4    Wide Area Network Topologies ........................................................... 18
     2.5    Routed or Switched Backbone ............................................................. 19
     2.6    Schools' Local Network Considerations ............................................. 20
     2.7    Separation of Administrative and Teaching Traffic ........................... 22
     2.8    Network Security .................................................................................... 22
3    Router Management ........................................................................................ 23
     3.1    Edge Equipment ..................................................................................... 23
     3.2    Router Security Policies ........................................................................ 23
     3.3    Firewall Features .................................................................................... 23
     3.4    Remote Management ............................................................................ 24
     3.5    Interface to the National Interconnect ................................................. 24
4    Provision of Network Services ..................................................................... 24
     4.1    Domain Name System (DNS) .............................................................. 25
     4.2    E-Mail ....................................................................................................... 28
     4.3    Web Services .......................................................................................... 29
     4.4    External Access ...................................................................................... 30
     4.5    Location of Network Services ............................................................... 31
     4.6    Disaster Recovery .................................................................................. 31
5    Support Services.............................................................................................. 32
     5.1    Technical Support .................................................................................. 32
     5.2    Network Monitoring ................................................................................ 33
     5.3    Information Dissemination and Staff Developme nt........................... 34
6    Advanced and Emerging Technologies ..................................................... 35
     6.1    IPv6........................................................................................................... 35
     6.2    IP Multicast .............................................................................................. 35
     6.3    IP Quality of Service (QoS)................................................................... 36
7    References ......................................................................................................... 37
Appendix A: Network Topology Discussion......................................................... 39
Appendix B: Glossary ................................................................................................. 44




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1 Purpose
School networks are complex and serve a rapidly developing set of educational
requirements, some of which challenge the technology and its security, implemented
within limited budgets. Many agencies are involved in providing the end-to-end network
service. There are networks on school premises, regional networks, Internet connectivity
and the National Interconnect via JANET. The whole forms the National Education
Network. At least three layers of educational management are involved: schools, local
authorities and national oversight. Suppliers include commercial network suppliers and
Internet services providers, Local Authorities (Las), Regional Broadband Consortia
(RBCs) and national agencies such as UKERNA. These agencies must work together to
produce a consistent, functional and secure IP network across the various management
domains.

This document sets out a number of considerations in the design of IP networks and the
basic network services provided over them. It does not attempt to recommend or specify
particular products or managed services; however it does describe best industry practice
in building and operating an IP network. In particular, it recommends open industry
standards, which should ensure that networks built in this fashion can function as part of
the global Internet. In addition, a network operating to open standards removes the need
to be tied to a particular supplier of equipment or services.

A number of other existing documents and standards are referenced. Some of these are
examples of policy or technical design; others are papers on how to prepare these. Where
possible, examples of best practice in the schools sector have been referenced
supplemented by examples from other sources.

1.1    Scope
The majority of the issues discussed here apply directly to RBCs/LAs designing and
building a wide area education network in their region. Schools must also be aware of
these issues in order for them to conform to the national standards for schools'
networking. The local network within the school is a key component in delivering end to
end performance and security in the National Schools' Network.

For example, while wide area IP routing may not be particularly interesting to the school,
it will certainly be interested in considering how it wishes to make use of e- mail and web
services. Different choices in these areas will have a high impact on the level of effort
that the school is required to provide; awareness of the issues in this document should
assist in understanding this.

Schools must also be aware of the demands the network and network services will make
of their own on-site network infrastructure. Investment in a feature rich wide area
network provides little return if the local networking and equipment at the school is
unable to fully exploit the resource.

This document does not address procurement issues.

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1.2    Target Audience
This document should be of interest to four principal audiences:

      Staff in schools involved with their school's internal network;
      LA or RBC staff designing, building or operating their wide area network; also
       those coordinating the networking activities of schools;
      Suppliers and service providers involved in the provision and management of
       local or regional schools' networks;
      Content providers who are making bodies of media-rich materials available to
       schools online.

1.3    Strategic Issues
Designing, building and managing an IP network service is a collaborative effort; the
RBC or LA network must meet the needs of the community it is intended to serve. These
needs may vary from region to region and will vary within the user community of a
single wide area network, for instance from the smallest infant to the largest secondary
school.

This document sets out a minimum standard of network features and services that should
be available to each school, and it is not intended to limit further services that may be
provided by the RBC/LA. Indeed, the RBC/LA network should be designed with
expansion in mind, to allow the network to evolve as schools' requirements grow.

The document is not intended to address network security issues in detail, more to note
areas where security plays an important role in network design. The accompanying
Network Security document is intended to provide in-depth information on network
security.

In designing a network, the RBC or LA first needs to consider the geographical location
of the sites which they need to serve, and work from this to produce a network topology
(section 2.4). Various transmission technologies are available (section 2.1), each having
its own set of advantages and disadvantages, as indeed will different modes of network
operation (for example, an IP routed network or a centrally based VLAN network).

The decision to use private or public address space (section 2.2) will have to be made.
Private address space eases the administrative burden, but requires extra implementation
work to allow privately addressed devices to access networks beyond the RBC/LA
border. Public address space relieves this work, and is architecturally cleaner, but
requires an arduous administrative application process for significant numbers of IP
addresses. This work is both in applying for the addresses themselves, and in designing
an IP addressing plan for the network around a very restricted resource.

The document also discusses the minimum set of network services that should be
provided over the network infrastructure. Support services including technical support,
network operations and information dissemination and training are also outlined. With

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these services in mind, appropriate technology can be selected for the internal network
infrastructure at the school.

The document refers to particular technologies and protocols. This is not meant to
preclude the use of other technologies; more a reflection on those found to be in common
use during the consultations with RBC and LAs. Any open, non-proprietary standards
based technology may be used, if it can be demonstrated to provide the level and type of
service required

The quality and availability of the broadband service a school receives will depend on the
local network infrastructure and the effectiveness of the network management by both the
suppliers and the RBC/LA.

1.4    Summary of Responsibilities
During the design and implementation of an RBC/LA network, many decisions will have
to be made, and work undertaken based on these decisions. Much of this work will be
the responsibility of the LA or RBC; however schools will have significant
responsibilities with respect to their own local network and to feed into the RBC/LA
design process.

This section summaries many of these activities, referencing the relevant sections of this
document.

1.4.1. Schools
School managers will normally be responsible for:

      Discussing their connectivity needs with their RBC/LA before installation. (2.1)
      Implementing IP addressing according to plans supplied by the RBC/LA. (Section
       2.2)
      Providing a suitable location for housing equipment necessary to connect to the
       RBC/LA network. (2.6.1, 3.1)
      Installing and maintaining the local on-site network to comply with industry
       standards. (2.6.2)
      Working with the RBC/LA support centre when necessary to rectify problems,
       whether related to on-site equipment or general networking problems. (2.4, 2.6.3)
      Ensure that network security is maintained. (2.8)
      Agree DNS requirements with the RBC/LA. (4.1.2)
      Inform the RBC/LA of updates to DNS data. (4.1.2)
      Working with the RBC/LA to determine optimal solutions to more specialised
       issues. (4.2, 4.3, 4.4)
      Educational decisions as to traffic priority and managing applications such as
       filtering and caching to reflect school policy.
      Co-ordinating external access, such as home to school access, where
       implemented.




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1.4.2. Local Authorities/RBCs
Local Authority/RBC managers are normally responsible for:

      Selecting suitable transmission technologies for the wide area network. (Section
       2.1)
      Designing, implementing and operating a suitable wide area network. (2.4, 2.6, 3,
       Appendix A)
      Providing connectivity to the global Internet, aggregating demand where
       appropriate. (1.5)
      Liaising with the DfES to ensure that the relevant criteria have been met with
       respect to the requirement for any interim asymmetric link technology for schools
       (e.g. ADSL or satellite). (2.1)
      Operating server and web hosting facilities. (4.3)
      Providing suitable locations on the backbone for network services. (4.5)
      Assembling a disaster recovery plan. (4.6)
      Notifying schools of requirements for locating on-site wide area network devices.
       (2.6.1)
      Providing access devices to schools. (3.1)
      Selecting a public or private addressing scheme. (2.2)
      Designing and implementing an IP addressing plan for both the backbone network
       and the schools' local networks. (2.2)
      Notifying schools of their responsibilities within this addressing plan. (2.2)
      Where private IP address space is chosen, operating a NAT service that fulfills
       requirements. (2.3)
      Operating proxy services as required. (2.3, 4)
      Deploying either an H.323-aware firewall or a proxy server, to facilitate IP
       videoconferencing. (3.3 and Videoconferencing document)
      Operating DNS services, for both the backbone network and schools' forward and
       reverse domains where required. (4.1)
      Operating an E- mail service. (4.2)
      Operating a Web hosting service. (4.3)
      Providing content filtering abilities. (4.2, 4.3)
      Providing methods of external access when requested. (4.4)
      Operating a support centre for schools. (5.1)
      Operating network management and monitoring. (5.2)
      Providing training and advice to schools. (5.3)
      Caching and content delivery services.
      Managing security and firewall services including change control.
      Network specification, procurement, service delivery monitoring and contract
       management.




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1.5    National Education Network
The National Education Network, connecting schools to each other and to the Internet,
comprises a number of different management domains, shown in the following diagram.
At the ends of the network are the computers and networks on school premises, for which
the schools themselves are responsible. Connecting schools in a geographic area are
systems and networks controlled by a Local Education Authority (LA) network, which
may be combined with, or a client of, a more general-purpose Regional Network.

Connecting these regional networks together is the National Interconnect via JANET.
Connection to the Internet should be provided at the RBC/LA or higher level; Internet
connections lower down the network are likely to cause serious operational, management
and security problems. Internet connection aggregation has clear benefits and, where
appropriate, it is recommended that this be considered by Local Authorities.




This structure reflects the management domains within the network: who is responsible
for systems and networks at each level. It is likely that the physical network will have the
same organisation, though the locations of the boundaries may vary between different
regions and schools depending, for instance, on networking technology and management
arrangements.

1.6    Interoperability and Standards
As described above the National Education Network consists of a number of different
domains, managed by different organisations. However, for a functional and secure
network to be achieved, the policies and technologies used in the different domains must
inter-operate. This will only be achieved by all parties working to agreed standards, either
formal international standards or UK-wide agreements. In some cases local agreements
on implementation may be made within overall standards. In networking, an arbitrary
decision in one management domain can affect the operation and security of all others.

Where they exist, International standards are to be preferred as they are better understood
and more likely to be supported by easily available products. In these documents, such
standards will therefore be highlighted when appropriate. However, it is important to note
that many standards, particularly newer ones, may still provide some flexibility of
interpretation. Apparently standards-compliant products may not always work together as
well as might be hoped, and prior testing to ensure compatibility is always advisable.




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The UK Government‟s e-Government Interoperability Framework (e-GIF) makes
recommendations with respect to the adoption of appropriate standards:
http://www.govtalk.gov.uk/interoperability/egif.asp.

There will also be a need for locally agreed standards, particularly regarding the
management and configuration of the network. For example if a school does not allocate
IP addresses to computers in a way agreed with the authority that runs the regional
routers, then the network is unlikely to be able to transfer packets as intended. In the area
of security, these local agreements are likely to dominate, covering topics such as the
types of traffic allowed on the Internet, how services such as mail and web browsing are
provided and how use and misuse of the network are to be accounted for.

The Internet Engineering Task Force (IETF) works to produce standards in use on the
Internet. These standards are published in request for comments (RFC) documents,
which are available from the IETF web site. It should be noted that the existence of an
RFC does not imply that a ratified (or draft) Internet standard exists. The IETF STD
document should be consulted to determine the status of the sub-set of RFCs which are
standards documents.

IETF RFC standards: http://www.ietf.org/rfc.html

Other telecommunications standards are produced by the International
Telecommunications Union (ITU). Historically these have been related to low level
telecommunications. More recently the ITU has taken an interest in the Internet area, and
the Internet community has adopted standards such as H.323 for video conferencing.

ITU standards: http://www.itu.int/ITU- T/publications/recs.html


2 Network Design
2.1    Transmission Technologies
2.1.1. Overview
IP may be delivered over many link level technologies, following much work by bodies
such as the IETF to define standard methods of transmitting an IP packet over different
link level technologies. Other proprietary standards are implemented by particular
equipment vendors – these are often slightly more efficient, but generally only work with
that particular vendor's equipment.

Lower layer link technology standards in the telecommunications industry are developed
by the ITU, as noted in section 1.6, and telecommunications service providers deliver the
majority of their services conformant with ITU specifications. An overview of the
underlying Digital Hierarchy technology is provided in section 2.1.9.




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The following sections describe the range of available transmission technologies, from
domestic ADSL to managed VPN services, including satellite and wireless options.

The Government‟s intention is that all schools have improved connectivity in order to
take advantage of Curriculum Online. The RBCs are working to a rolling programme
which is connecting schools with a minimum of 2Mbps “two way” broadband. This is
the national standard expected by Government for all schools and other institutions with a
DfES number.

However, as an interim measure in order to obtain short-term improved connectivity for
more schools, asymmetric technologies such as ADSL or satellite (both described below)
should be considered where available and affordable, principally as a replacement to
ISDN. These technologies provide better connectivity than ISDN but they do not support
real-time applications such as video-conferencing. Access may not be possible to some
online multi- media or highly interactive packages.

Schools will need to discuss their needs with their RBC or LEA before these interim
technologies are installed. The RBC or LEA will liaise with the DfES to ensure that the
relevant criteria have been met.

DfES Standards Fund Guidance
ICT in Schools Standards Fund Grant 2004-05
Guidance for Schools and LEAs
http://www.dfes.gov.uk/ictinschools/funding/

DfES Policy on Connectivity
ICT in Schools Standards Fund Grant 2003-04
NGfL Grant 601a: Information for LEAs and Schools
http://www.dfes.gov.uk/ictinschools/funding/composite.cfm?partid=46


2.1.2. Digital Subscriber Lines (DSL)
Digital Subscriber Lines are widely available from many ISPs, though virtually all use
the underlying existing copper telephone infrastructure owned by BT. Currently the
maximum speed is around 9Mbps both ways and the maximum range for DSL is 6Km
from the nearest exchange. The range is calculated along the route of the copper, rather
than by radial distance from the exchange. The „enabling‟ of an exchange is usually
triggered once a sufficient number of users have registered an interest in digital services.
ADSL is a range of asymmetric DSL services, where the upstream link (from the
customer) is at a significantly lower data rate than the downstream link (to the customer).
This is deemed reasonable because most domestic traffic is as a result of browsing web
pages and receiving emails, rather than sending large files. Commonly the upstream link
runs at one quarter of the speed of the downstream link. The downstream links vary in
speed from 512Kbps to 2Mbps, depending directly on the distance from the customer to
the exchange; the maximum performance being achieved within the optimum distance of
3.5Km from the exchange.


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Domestic versions of ADSL operate with a contention ratio of up to 50:1 (i.e. shared by
up to 49 other users) and are only suitable for one or two concurrent users. Business or
premium ADSL services operate at improved contention ratios from 5:1 up to 20:1.

Generally the asymmetric solutions are intended for use by a small number of users in a
domestic or small office environment and are not recommended as long term Broadband
solutions for schools. However, in some circumstances, such as very small rural schools
that do not yet require the more demanding services such as conferencing, it may be
necessary to use such solutions as a temporary measure, while making or planning the
transition from ISDN to Broadband. The current DfES ICT in Schools Standards Fund
Grant 2004-5 guidance document does take this into consideration (31b: Connectivity,
paragraph 15). In these cases it is suggested that the premium ADSL services, which
provide improved contention ratios, be considered.

Symmetric DSL (SDSL) can provide up to 8Mbps both ways, and may provide a cost-
effective approach to delivering the bandwidth currently required.

Some carriers provide lower cost contended 2Mbps services based on SDSL and these
may be a viable option during a transition to using leased lines. However, when
congested, if such a service is contended at 20:1 it may prove to be no better than a
conventional ISDN2 line at 128Kbps. Where available, a service with a lower contention
ratio, say at 5:1, may provide a more viable interim solution.

Inexpensive telephone grade copper pairs, providing symmetrical circuits called EPS8 or
EPS9 may be purchased directly from BT only. These options require a high degree of
technical knowledge to implement, as customers have to supply their own circuit
termination devices to create a broadband link, and as a result are not recommended.

Some ISPs have announced that customers in parts of London can purchase an
uncontended ADSL service. This service provides a download speed of 2 Mbps and an
upload speed of 250 Kbps, but has the advantage that the bandwidth is not shared
between customers. The maximum distance from the exchange is 3.5 Km. In 2003,
about 20 exchanges in London were enabled for the service and the roll out across the
UK will depend on sufficient interest being shown.

2.1.3. Leased Lines
Leased lines are widely available from all telecommunications providers and are often the
only choice for bandwidths greater than 2Mbps. They are available in rural and many
remote locations.

Under an agreement with OFTEL (now OFCOM), there is a special BT tariff for
Megastream (2Mbps) leased lines available to schools, called Learning Stream. This is
currently widely deployed in the schools sector. Learning Stream is available essentially
at bandwidths of 2 Mbps and 34 Mbps (High bandwidth Learning Stream), the 8 Mbps
has been discontinued. Some local authorities implement clusters of schools which share
a Learning Stream link.


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An overview of the Digital Hierarchy technology, which underpins these leased line
products, is provided in section 2.1.9.

2.1.4. Short Distance Ethernet Services
Recent advances in fibre optic technology and switching electronics, as well a greatly
reduced bandwidth costs, have meant that it is now both possible and cost effective to
extend Ethernet services on a regional level.

LAN Extension Services products are offered by a number of telecommunication carriers
under various brand names (e.g. BT‟s LES2, LES10, LES100; Thus‟s City Ethernet; etc)
for short haul point-to-point distances up to 25Km. Flexible interfaces allow customers to
select service speeds and connections that best meet their individual needs.

Link status of LES circuits can be very hard to determine as line faults or errors are not
propagated through the network. The Ethernet Switch devices are owned and operated by
the Service Provider. The customer‟s equipment that connects to the Service Provider‟s
switch sees no change of state because the Ethernet switch is still up and active. These
failure modes that cannot be detected by the customer rely on layer 3 protocols to detect
faults/ errors. This can be problematic when it comes to network management.

The low costs associated with these products present an attractive value proposition for
network planners but the limitations discussed need to be considered especially with
respect to connections where reliability is critical. Customers opting for LAN Extension
products should fully understand the technical specification of the solution being offered
and the possible drawbacks.

2.1.5. Long Distance Ethernet Services
These are relatively newer services available from a number of telecommunications
providers, where the distance limitations are removed. They are typically priced so that
bandwidth can be subscribed to in steps, below the physical capacity of the link, and
therefore may be more cost effective than leased lines. Examples include BT‟s
Megastream Ethernet and Thus‟s National Ethernet.

2.1.6. VPN Services
These are available from a number of suppliers under a variety of names (e.g.: BT‟s
Metro VPN, IP Clear.). These are managed services, often viewed as “cloud” network
services. These are potentially useful where there are many sites to connect together, but
the tariffs can be complex and the costs may be high. Such a VPN solution is likely to
limit the available IP features over the connection, whereas other solutions do not have
this limitation.

2.1.7. Satellite Technologies
One-way satellite systems provide a down link only and interaction therefore necessitates
an uplink via a dedicated telephone line. Two-way satellite links provide asymmetric
services similar to premium ADSL, with a contention ratio up to 20:1.


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Two-way satellite systems (e.g. Gilat 360 and Astra BBI) are available from a number of
suppliers, and can be deployed virtually anywhere in the UK at a fixed cost. The monthly
costs compare with those of a premium ADSL service, although there are also significant
initial installation costs. Most suppliers will provide options to buy or lease the
equipment. In some regions, e.g. Wales, there are two-way satellite subsidy schemes in
operation for those in remote areas. A dedicated 2 Mbps link would cost about ten times
that of a typical leased line connection.

While the high latency associated with satellite networking precludes the use of real- time
applications such as videoconferencing and Voice over IP, satellite services are of
significant value in rural and remote areas.

Reference: http://www.ja.net/development/network_access/satellite/trial.html


2.1.8. Wireless
In rural or remote locations there may be few alternatives available other than to use
licensed or license-exempt radio frequency (RF) technology to provide communication
links.

The deployment of a wireless network requires significant technical and operational
expertise if a reliable service is to be achieved. Furthermore, any wireless transmission
solution has to be well designed and managed; it is never a substitute for a wired
equivalent when one is available. The greater susceptibility to interference means that
contracts with service providers must be tight, guaranteeing fast detection of failing, or
failed, wireless links. When such situations occur, speedy resolution of the issue should
be enforced. The service level agreement (SLA) with a supplier should be checked in
detail to ensure that suppliers adequately monitor and mana ge them.

However, there may be further commercially available options appearing as a result of
the recent opening up of new frequencies (e.g. Band C - 5.8GHz) for such services.

The maturity of this technology has permitted the use of microwave links as the major
trunk channel for long distance communication over „fixed wireless‟. Bandwidth
capacities range from single E1 to STM-1 (155Mbps). Wireless (or "free-space")
communication technologies are, however, susceptible to interference from the weather,
particularly rain. Microwave systems provide point to point links which are generally
used to link together networking infrastructure devices in the same way as a leased circuit
might be used. Point-to-point microwave links are terrain independent so long as there is
line of sight between the sites at each end of the link. Where there is no direct line of
sight, it may be still be possible to implement a link, via one or more intermediate
stations located on radio masts or tall buildings.

Wireless Ethernet technology (license-exempt “WiFi”) provides multiple access
networking over the air to many clients using devices known as wireless access points.
These systems are commonly used to provide LAN connectivity, but can also be used to


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provider wider-area network coverage. With appropriate antennae, it is possible to
provide large areas with wireless Ethernet. Further access points can be added within
range of each other to extend the coverage over larger and larger areas. This might be
used with just two access points, linking two schools located close to each other - in
which case both schools could make use of a single broadband connection. Other
applications featuring several access points with overlapping coverage might allow a
small community to have access to the broadband connection at the local school. These
are often known as "wireless mesh" networks. Wireless Ethernet is in general more prone
to, and susceptible to, interference effects. Wireless may not be the optimum solution for
point-to-point links, but it is relatively easy to deploy at low cost.

Wireless networks of any kind pose a greater security risk than wired networks.
Microwave links are relatively difficult to intercept, as they operate over a tight signal
beam; however wireless Ethernet and satellite signals are easily intercepted. When using
wireless solutions it is critical that traffic is encrypted for transmission over the air. Care
is needed when selecting the encryption mechanism, to ensure that it is not easy to crack.
For example, the wired equivalent privacy (WEP) system of 802.11 standard wireless
Ethernet systems has been shown to be relatively straightforward to crack. Many
organisations therefore operate additional security measures over their wireless Ethernet
systems. Further discussion of wireless security issues is presented in the Network
Security document.

Infra red and laser optical links can be used to provide connectivity between buildings;
however, a clear line of sight is required and the service can be affected by certain
weather conditions. These links are practical only over short distances, less than 1.2Km,
and are sometimes used in conjunction with an unlicensed radio backup.

2.1.9. Overview of Digital Hierarchy Technology
PDH (Plesiochronous Digital Hierarchy) is a technology used in telecommunications
networks to transport large quantities of data over digital transport equipment such as
fibre optics, copper and microwave radio systems. It is a widely deployed transmission
system, traditionally used for low speed leased line data circuits from 2Mbps (E1) to
140Mbps (E4). However, it lacks the fault detection, performance monitoring capabilities
and recovery mechanisms offered by the newer and more efficient SDH (Synchronous
Digital Hierarchy).

SDH is bandwidth- flexible and, although based on multiples of 155Mbps (STM-1) up to
40Gbps (STM-256), it permits networking at the 2Mbps, 34Mbps and 140Mbps levels,
thus accommodating the existing PDH signals.

SDH differs from PDH in that the exact rates that are used to transport the data are tightly
synchronised to network based clocks. Therefore the entire network operates
synchronously enabling the use of extremely high transmission rates. Unlike its
predecessor, SDH is an intelligent system that provides advanced network management
and a standard optical interface. SDH devices provide extensive mechanisms for fault
detection, notification and recovery. Fault detection and the appropriate path protection
switchover are achieved within milliseconds; therefore circuit failures can go unnoticed


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by the end user. Path protection is achieved by employing a self- healing ring architecture
that is able to reroute traffic over backup transmission paths in the event one fails.

These capabilities are only made possible by the use of complex and advanced
technologies which drive up the cost of associated equipment. However, SDH does
provide supreme resilience and reliability levels and is expected to provide the transport
infrastructure for worldwide telecommunications for the foreseeable future.


2.2    IP Addressing
2.2.1. Overview
To connect to the Internet, a globally visible IP address is required. As these are a scarce
resource, it has become an arduous process to obtain large numbers of these "public"
addresses. Other than the perceived barrier of a complex application process, public
address space is available to meet any size of requirement that can be documented and
justified, according to Internet Registry guidelines.

The most difficult of these guidelines requires that an applic ation for a sizeable number
of public IP addresses provide a detailed breakdown of proposed address use in an IP
addressing plan. No provision of spare addressing is permitted for administrative ease,
which would entail the use of different allocation and subnet sizes depending upon the
size of school. No single IP addressing scheme could be applied to every school on the
RBC/LA network.

The Internet Registry that serves Europe is the RIPE NCC; further information on public
IP address application requirements is published on their web pages.

Because of these tight restrictions on assignment of public IP addresses, many networks
choose to use private IP addressing. Private IP addresses are reserved by the Internet
Assigned Numbers Authority (IANA), and will never be routed on the public Internet.
Any part of this reserved address space can be used by any number of organisations
without any prior applications or registrations; these address ranges are set out in IETF
RFC1918.

Private IP address ranges: http://www.ietf.org/rfc/rfc1918.txt
The IANA: http://www.iana.org/
RIPE NCC: http://www.ripe.net


2.2.2. Public and Private Addressing Schemes
At first sight, using private address space for internal connectivity may seem ideal, as it
removes the constraints on planning imposed by public address allocation. However,
there are some considerations when choosing to use private address space.

Private address space is, by definition, private. Organisations connected to the same
network will be able to interconnect using their private IP addresses; however it will be


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impossible to make connections to other networks, particularly the Internet. Another
interesting issue is what happens when two organisations merge. If both are using the
same part of private address space, work (most likely renumbering) will have to take
place to enable both networks to interconnect.

To connect to external networks, a privately addressed network will generally use NAT
(see below), or some form of proxy service - for example, a web proxy. By default, a
publicly addressed network gives full local Internet connectivity. This in itself may, of
course, be undesirable. As discussed in the Network Security document, a "default deny"
policy is often the best policy; public IP addresses provide the opposite (“default allow”).

With private address space, connections to internal hosts cannot be originated from
outside the network, unless specifically enabled in the NAT configuration. With public
address space, all connections are possible, unless specifically disabled by means of
packet filters or a other firewalling techniques.


2.2.3. Provider Aggregateable and Provider Independent Addressing
Public IP address space is divided up into types; provider aggregateable (PA) addresses
and provider independent (PI) address space. Before the early 1990s, all address space
assigned was PI - the IP addresses used on a network bore no relation to any other
organisation other than that using them.

As a result, the global Internet IP routing table had to maintain an entry for each and
every IP network in use around the world. As the Internet grew, it was clear that this was
not going to scale.

Address space is now almost always assigned as PA. Service providers are assigned
blocks of address space for onward assignment to their customers. This allows the
provider to use a single route in the global table to cover many customers, instead of
needing to add a route for each specific customer network.

A major consideration in choosing between PA and PI addressing is what happens when
a network changes service provider. To retain the routing economies of PA space, routes
from one provider's address blocks should not be visible via a different service provider
(although with Internet multihoming it is often the case that there is no way of avoiding
this).

This implies that when changing provider, an organisation must renumber the whole of
its network to new PA space. Where NAT is used, this is not too great an issue, as it is
simply a matter of changing the NAT configuration to use a new pool of PA addresses.

However, where public addresses are used to number an entire network directly, mo ving
to the new PA space is a significant issue.

(Note that the holding of PI space often involves the payment of service and/or
membership fees to an Internet IP number registry.)


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2.3     Network Address Translation
Network Address Translation (NAT) is a mechanism which permits hosts on a locally
numbered IP network to appear to be using different addresses beyond an external
border; typically a connection to a service provider. NAT is often used with a network
numbered with private address space to permit external connectivity from local hosts.
NAT is usually configured at the border of the privately address network, and essentially
rewrites the internal IP address to a public IP address.

      IP address:
      10.0.0.100

                                             Translate          External network
                                            10.0.0.100          communicates using
                                                to              194.12.27.23
                                           194.12.27.23


                    Local Net work                               External Netwo rk



                                     Local to external
                                     address translation
                                     happens here


This may be a single external IP address, where many internal addresses are all translated
to that one address. It is also possible to configure a pool of external addresses, allowing
mapping between many external address. The mapping can be configured to be dynamic,
on a connection by connection basis, or may be configured to map specific internal hosts
to one or more specific external IP addresses.

For connections made outwards from the internal network, dynamic mapping is most
likely to be sufficient. Static mapping is mostly used where it is necessary to have
external access to an internal host – for example, a web server running on a machine on
the internal network. In such cases, it is almost always essential to have a one-to-one
mapping of public address to private address. For example, if two web servers map to the
same external IP address, how would the NAT configuration know which internal box to
forward the request to? Unless one server was to operate on a different port number,
there would be no method of distinguishing between connections at the NAT level.

Configuring direct inward access to a network immediately decreases the security of the
network. In almost all cases, external access requirements can be met using more secure
technologies, such as proxy servers and virtual private networks (VPN).

Originally, NAT only changed information in the IP packet header; however some
services such as H.323 videoconferencing embed IP addresses in the data portion of the
packet. To enable the service to function, these IP addresses also need translating.




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Most NAT equipment now has the functionality to detect data flows from services such
as H.323, and will translate IP addresses in the packet data. Any organisation operating a
NAT device on the RBC, LA or school network must ensure that the device provides
support for any services such as H.323 that schools might be using.

Care must be taken to prevent overloading on a NAT device, or devices. The resource
requirements (e.g. CPU load and memory) for NAT are proportionate to the number of
hosts on the network, and not the bandwidth of the network. A network of many
thousands of hosts will have the same demand for NAT resources regardless of whether
the external connection is 2Mbps or 100Mbps.

NAT is often referred to as a security tool, which it is not. Elements of NAT do certainly
contribute towards some level of security, by essentially rendering internal hosts
unreachable from external hosts by default. However, it is no substitute for a well
thought out and implemented security framework.

2.4    Wide Area Network Topologies
IP networks typically consist of two major components:

      a backbone infrastructure, consisting of points of presence ("PoPs")
       interconnected by high speed lines
      an access infrastructure used to connect customers and external networks to the
       backbone (also referred to as "aggregation")

Access infrastructures typically connect several sites to a common local access PoP using
short distance links; the PoP is then itself connected to the backbone. In some topologies,
access PoPs and backbone PoPs may well be at the same location; in others, access PoPs
may be used for economic reasons, to allow several sites to share a single long distance
(and therefore often expensive) link to the backbone.

Internet backbone infrastructures are generally constructed using a ring topology, making
the network more resilient to a single backbone link or equipment failure. Should one
link or switch/router fail in the ring, traffic will re-route the longer way around the ring
(assuming correct configuring of the routing technology being used, of course).

Some use star based topologies, where aggregation points are directly connected to a
central location. This is a more straightforward topology, but can be less resilient. If
multiple aggregation points use the same single link to the backbone, failure of that link
will affect many sites. Worse, if the equipment at the central location is not sufficiently
redundantly provisioned, a failure here could disable the entire network.

Perhaps the worst topology is a chain of routers providing access to the core location.
This provides progressive aggregation of access links, but failures along the chain have
disastrous consequences.

Appendix A discusses these network topologies and resilience issues in further detail.



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In addition to backbone links and equipment, many networks choose to operate an access
device, commonly an IP router, at each customer site, extending the hand off (or
demarcation) point to the customer beyond the telecoms supplier's equipment. This
access device is typically located next to the supplier's equipment.

This allows for easy monitoring of the far end of the site link as it does not rely on any
customer equipment, and also aids in troubleshooting problems. If the site access device
is reachable from the wide area network without any problems, then problems are very
likely to be within the local site network infrastructure.

Individual access devices at each site also enable site-specific configuration to be made
locally - for example packet filters, or quality of service configurations.

Capacity planning is often a difficult issue, particularly if planning an entirely new
network. Backbone capacity is seldom provided on any network on the assumption that
customer access links will be near 100% loaded, so a 1:1 ratio of access bandwidth to
backbone bandwidth is almost never seen.

Access links on school's networks are often heavily loaded; experience in some networks
shows that an access to backbone bandwidth ratio of around 4:1 is likely to be required.
It may be able to improve on this ratio by co-ordinating closely with schools to determine
the mix of traffic on their access links. In many cases there will be a sizeable proportion
of traffic at peak times that is not directly educationally related - managing this mix by
disabling less important traffic at busy times may improve performance without the
additional cost of capacity upgrades.

2.5    Routed or Switched Backbone
With the physical backbone established, the method of providing IP interconnectivity
between the schools, network services, the national interconnect (via JANET) and other
external networks should be selected.

Many networks operate a routed IP network, which generally makes the most efficient
use of bandwidth. An IP routing protocol (such as OSPF or IS-IS) carries connectivity
information for all IP networks connected to the RBC/LA backbone. Traffic is routed via
the best available path to its destination (assuming optimal configuration of the routing
protocol).

Other networks may choose to extend VLANs from central locations to individual
schools, so that regardless of the physical topology of the network (see Appendix A) ; all
traffic is brought into a central location before being forwarded to its destination. This
arrangement will not usually deliver efficient use of capacity on the network, as much of
the traffic on the network will cross the same link twice: once on the way in to the central
location, and again on the way out.

IP routed networks will generally deliver more efficient use of bandwidth but can be
more complex to configure than VLAN based networks. VLAN networks, on the other



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hand, may assist in the implementation of network security, by bringing all traffic to
central locations.


2.6    Schools' Local Network Considerations
2.6.1. Physical Issues
In most cases, two pieces of equipment will require housing on-site at the school: the
termination device from the telecommunications supplier on which the wide area link is
delivered, and the access router to which the link is connected.

These devices are typically relatively small, and have no special environmental demands
other than power and adequate ventilation, as for any other type of electrical device that
produces heat. The access router may have internal fans that generate significant
amounts of noise, and so may not be suitable for location in a general office environment.

The RBC/LA should inform schools of the space needed to house on-site equipment, and
any special considerations for its location well in ad vance of delivery and connection to
the network.


2.6.2. School LAN Infrastructure Issues
A well designed and provisioned local network will enable the school to benefit as fully
as possible from its broadband connection. The network infrastructure at the school must
be able to comply with the IP addressing plan, DNS architecture and other requirements
of the RBC/LA network.

Suitable equipment will be required to connect to the hand-off point for the wide area
network; this hand-off will most often be a full-duplex Ethernet connection (although the
actual upstream connection off-site may be of a lower speed).

To successfully exploit the RBC/LA network and the Internet beyond, adequate capacity
must be provisioned on-site, particularly if higher bandwidth applications such as video
conferencing are expected to be used. Experience so far has shown problems associated
with the local network at the school to be the cause of connectivity problems, and not
lack of capacity in the wide area network.

The on-site networking technology will almost certainly be Ethernet based; many schools
operate using Ethernet hubs, which are now an outdated technology and undesirable. An
Ethernet hub is a simple shared medium, where all traffic on the hub is replicated onto
each port, regardless of whether it is of interest to the device connected to that port.

This effect is compounded in many Ethernet hub designs when hubs are interconnected.
For example, two eight port hubs connected together will cause 16 ports worth of traffic
to be replicated on each hub port. Hubs with slightly more intelligence may not replicate
traffic to this extent, but in a large network of hubs, problems with the protocol used to



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prevent unnecessarily replication can cause unexpected, and often intermitte nt and hard
to trace, network problems.

It is recommended that schools should operate a full-duplex switched Ethernet network,
at a speed of at least 100Mbps. Ethernet switches are in general more feature rich
devices, allowing specific management of individual ports and facilities such as virtual
LANs (VLAN). VLANs can be useful for separating out logical IP networks operating
over the same physical infrastructure - one such use could be to separate administrative
and teaching traffic (see later section).

A single Ethernet network operating with many hundreds of hosts will present
performance problems. Ethernet uses a protocol called CSMA/CD (Carrier Sense
Multiple Access / Collision Detect). It is the protocol that allows multiple devices to
access a shared Ethernet or Fast Ethernet network. These devices form what is known as
a collision domain in which only one device may transmit at any one time. The "Carrier
Sense" function checks the wire to see if any other node is already sending something. If
the LAN appears to be idle, then the node can begin to send data. However two nodes
can begin to send data at the same time, and their signals will "collide" nanoseconds later
resulting in a collision. When such a collision occurs, the two nodes stop transmitting,
"back off", and try again later after a randomly chosen delay period. While the two
devices involved in the collision are waiting to resend, it's possible for another device to
send a packet, which may also be involved in another collision.

An Ethernet network based on switching overcomes this effect. Ethernet switches
separate the network into microsegments, which should be single host segments. This
creates collision-free domains which operate separately from each other. Further
performance increases can by gained by using layer 3 enabled switching, or by splitting a
large network into several VLANs. Using multiple VLANs requires local IP routing
functionality to interconnect the VLANs, which is typically provided by a separate IP
router.

A switch can also provide improvements in performance and security - notably a PC
connected to an Ethernet hub has the ability to snoop on all traffic on the hub, if not the
entire local network. A switch passes only traffic relevant to the connected device,
including broadcast and multicast traffic relevant to the Ethernet or VLAN configured on
that port.

2.6.3. Operational Issues
Unless maintenance or repair work is being undertaken or as instructed by the RBC/LA,
the RBC/LA network equipment based in a school must never be switched off, as this
may cause an alarm on the network monitoring equipment and may prevent overnight
updates or backups over the network.

From time to time it may be necessary for the school to permit third party staff access to
the on-site RBC/LA network equipment. For example, if there is a fault on the
telecommunications termination device or failure of the access router, staff from the
supplier or a maintenance contractor will need access to repair or replace the unit.


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In other circumstances, the RBC/LA may need to call on the assistance of school staff to
reset the equipment, or otherwise assist with troubleshooting of network problems. In
such cases, it is essential that school staff can easily and safely gain access to the
telecommunications equipment and network access device. The RBC/LA should ensure
that at least one member of school staff is shown how to make these checks. If possible
this staff member should be present at the installation of the equipment.

The school must ensure that at least one member of staff is able to perform these checks,
and that the RBC/LA is notified should the staff member responsible change. The
RBC/LA must undertake to visit the school to familiarise any new designated staff
members with the equipment and procedures.

2.7    Separation of Administrative and Teaching Traffic
Some schools may feel it desirable to segregate administrative traffic from teaching and
other education traffic; which could be achieved by the use of a separate physical
infrastructure, or a VLAN configuration.

The DfES Standards Fund Guidance clearly states that the delivery of „whole school
networks‟ is a priority. Schools should make optimum use of their hardware and software
through ensuring that they have an integrated local area network (LAN) to provide easy
and timely access to ICT tools for the whole school workforce and that this is capable of
providing both curriculum content and management information. Therefore, schools
should not expect that the RBC/LA equipment will be capable of providing direct
connectivity to more than one separate physical LAN.

Where a school chooses to implement two or more VLANs, the responsibility for
providing interconnectivity between the VLANs lies with the school. This will involve
the provision of an IP routing device; some Ethernet switches may be capable of
performing this function. On the other hand, some local authorities provide access to
administrative services only via VLANs. The hand-off point from the RBC/LA network
should be capable of accepting VLANs from the school, even if the traffic is combined at
that point.

DfES Standards Fund Guidance, Grant 31a: Infrastructure etc Paragraphs 9 and 10:
http://www.dfes.gov.uk/ictinschools/funding/composite.cfm?partid=24


2.8    Network Security
Network security is, without question, a vital part of any network design, and as such is
detailed separately in the Network Security document.




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3 Router Management
3.1    Edge Equipment
Each site will require an access device, which will be the demarcation point between their
LAN and the WAN and in many cases the management boundary between the school and
local authority.

It is recommended that a layer 3 router is used, rather than a layer 2 switch with IP
routing capabilities. This is based on experience that shows performance and capability
issues with the latter especially relating to advanced features e.g. packet filtering. The
router should also use dedicated hardware, rather than router software on a PC.

This device will support a WAN interface that will terminate the circuit from the
RBC/LA. Taking budgetary constraints into consideration, it may be appropriate to use a
device that supports modular interfaces that can be swapped out if the access circuit is
upgraded rather than having to replace the whole chassis.

It will also support a local interface(s) which will connect the school‟s LAN(s). The most
widely used LAN technology used is Ethernet of which there are various standards which
can run at 10/100 or 1000Mbs.

The use of „Static routes‟ to route traffic to and from the schools network should be
adequate and will simplify configuration of the devices. However, if there is a need to
multihome sites then advanced dynamic routing protocols like Border Gateway Protocol
(BGP) may need to be supported (see Appendix A).


3.2    Router Security Policies
Being on the management boundary the „edge device‟ would be the ideal place to
implement security policies for that site. This is unless it is agreed that a common
security policy will be applied to all schools in which case the policies can be set further
into back into the Service Providers network.

Security policies are dealt with in detail in the Network Security standards document.


3.3    Firewall Features
Experience has shown that many security control features required by network
administrators are in fact bundled into certain versions of operating systems provided by
the major routing equipment vendors. This can save on cost and can reduce management
complexity associated with advanced security products like firewalls. The
implementation by schools of their own firewalls independently of the RBC/LA central
firewall service is likely to lead to complications. In order to enable IP videoconferencing
it is recommended that each local authority deploys either an H.323-aware firewall, or a
proxy server alongside the existing firewall. The Videoconferencing document covers
firewalls and proxies in relation to H.323 traffic.

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The Network Security document discusses firewalls and their implications for security in
more detail.

3.4    Remote Management
In many cases edge equipment will be managed, either routinely or in emergencies from
a remote location using „in band‟ connectivity, supported by the SNMP protocol. In the
event of access link failure this function would be lost along with the ability to properly
diagnose the fault that has occurred.

It is therefore, strongly recommended that provision is made for some sort of „out of
band‟ management. This can be achieved by using an analogue modem; ISDN dial up or
an ADSL connection.

3.5    Interface to the National Interconnect
In summary the Interconnect Service provides:

      An IP- level interconnection between each RBC Network and every other RBC
       Network subscribing to the Service.
      Connectivity to all organisations connected to JANET.

The Service does not provide transit from a RBC Network to the wider Internet.

The border router nominated by the operator of the RBC Network peers with a
SuperJANET backbone router using the BGP4 protocol.

The operator of each RBC Network is required to ensure that the preferred route for
traffic between their network and all other RBC Networks and JANET sites is via the
Interconnect service.

The technical specifications and recommendations for interfacing with the National
Interconnect are explained in the following document:
http://www.ja.net/schoolsbroadband/technical_specs.pdf



4 Provision of Network Services
Schools, of course, require not just IP connectivity but also a number of basic network
services, such as Domain Name Service (DNS), e- mail, web services and forms of
external access to the network. The latter may be, for example, for students to access
their e- mail or work from home, or for service suppliers to make connections to
administer their services.




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4.1    Domain Name System (DNS)
DNS enables the mapping of names to IP addresses and vice versa, and underpins almost
all other network services. Following network connectivity, it is perhaps the most
important part of an IP network. There are two main areas to consider; providing service
to schools to enable the lookup of external information (a "resolver"), and providing
information about how to reach services on the RBC/LA network ("name service").

4.1.1. Internet Domain Names
A complete Internet domain name consists of two parts - the name of the piece of
equipment (for example, a PC) and the domain name in which it is named. Such names
are referred to as "fully qualified domain names" in DNS terminology.

For example, a PC named server1 within an organisation using the domain name
something.co.uk would have a fully qualified domain name of
server1.something.co.uk .

Many organisations also choose to name services in the DNS the web site of
something.co.uk would most likely be reachable at www.something.co.uk.

Any one piece of equipment may have multiple names - the DNS allows for the
configuration of aliases. pc23.something.co.uk might well be operating a Web server
that was reached as www.something.co.uk at the same time as an E- mail service reached
as mail.something.co.uk.

There is a standard domain naming scheme for schools in the UK. Each school has a
standard name built from the name of the school, the LA in which is situated, and the
ending of "sch.uk ". For more details, see:

Standard school domain names:
http://www.nic.uk/SecondLevelDomains/AboutSecondLevelDomains/schuk/England/Inf
ormationForTagHoldersAndLeas/InformationForTagHoldersAndLeas.html


4.1.2. DNS Structure
The DNS architecture is based on a hierarchy of nameservers, arranged in a tree structure.
A request for a name to address (or vice versa) mapping traverses this tree until it reaches
a server that holds the required information. Servers towards the leaves of the tree hold
more and more specific information; those towards the root hold more general
information, sufficient to refer queries onwards to nameservers that hold more detailed
data for the required mapping.

The data configured on a nameserver about a domain is known as a "zone" file. In
nameserver terminology a zone is a set of domains under one administrative
management. An end site will typically require at least two zones to be operated - one to
map names to IP addresses (the "forward" zone) and one to map IP addresses to names
(the "reverse" zone).


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As DNS service is crucial to the straightforward use of the Internet, the standards permit
both a primary (or "master") nameserver for a domain, and one or more secondary (or
"slave") servers. This helps to make the DNS resilient to failure, subject to careful
consideration of each nameserver.

At start up, a secondary server retrieves a copy of the zone files it is serving from the
primary servers for each zone. It then periodically checks with the master for updates
(more recent nameserving software allows the primary to notify secondary servers after
changes are made).

Operation of forward and reverse domains provides information to external networks; to
enable mappings for external networks from internal hosts, a name lookup (or "resolver")
service should be provided. Most (if not all) nameserver software is capable of acting as
both a nameserver and a resolver.

When using private IP address space, DNS services become slightly more complex to
configure. Hosts will use their private address space to communicate with other internal
hosts - applications and users will be unaware that NAT is in use when communicating
with networks external to the RBC/LA. (This in itself causes problems for some
applications - see earlier NAT discussion).

The nameserver and resolver configurations in such cases need to provide different
information depending upon the source of the query. Lookups from internal hosts will
need to return the correct internal information; those from external hosts will have to
return information based on the public addresses. This is often referred to as operating
"split view" DNS.

In many cases, nameservice, resolving and split view can be configured on the same
server, although many choose to operate two sets of servers internally. One to serve and
resolve internal queries (returning information based on private IP addresses), and the
other to serve the data from the zone files based on public IP addresses to external
networks.

RFC1034 and RFC1035 define the base standards for DNS; several other RFCs provide
updates.

DNS standards:
http://www.ietf.org/rfc/rfc1034.txt
http://www.ietf.org/rfc/rfc1035.txt
http://www.ietf.org/rfc/rfc1996.txt
http://www.ietf.org/rfc/rfc2052.txt
http://www.ietf.org/rfc/rfc2136.txt

4.1.3. Nameserver Provision and Operation
When provisioning nameservers to provide information about local host addresses for
external hosts, thought should be given to their location. It would appear that providing a


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secondary server (or servers) should improve resiliency; however if the secondary server
is connected to the same LAN, with the same path to the Internet as the primary server,
any failure other than that of the primary itself will also disconnect the secondary from
the network. It is therefore sensible to provide at least one off-site secondary server,
preferably outside the local network.

Availability of DNS data when the access link to a site or network is down greatly assists
applications such as e- mail. In the case of e- mail, a link failure may disconnect the
primary DNS server and local e- mail server, but remote e- mail servers can still lookup e-
mail delivery information in the DNS, from the secondary servers.

In some cases, this will prevent e- mail being returned to the sender, as no mail routing
information can be found. In others, there may be backup e- mail servers that can accept
the message, or it may be that the e- mail service for the site is located off-site anyway, so
the message can be delivered directly.

Many service providers provide secondary DNS service, or indeed, contract to operate a
well engineered primary and secondary DNS service on behalf of their customers.

4.1.4 Zone File Maintenance
Close interworking between the schools and their RBC/LA is required to maintain correct
name to address mappings. A mechanism must be in place where either the RBC/LA
network provides standard name and address mappings for each school, or for the school
to administer its own naming and addressing, and feed this information back to the
RBC/LA so that appropriate DNS entries can be configured.

Once the information has been gathered, its configuration into the nameserver software
itself will vary with different software products. Typically a Unix based nameserver will
be based around plain text files which are directly edited, either manually or via locally
customised interfaces. Other platforms will use graphical user interfaces and other
methods.

Some operating systems choose to notify nameservers of their IP address and hostname
upon boot, or acquisition of an IP address. This is handled using a DNS feature known as
dynamic update, and was primarily intended to allow hosts whose IP address regularly
changed to maintain a valid entry in the DNS. (For example, users of most Internet dial-
up services receive a different IP address each time they connect).

It is unclear how useful this facility is in the schools' networking environment; however
the feature is mentioned here for completeness. The service is not essential, but should
be implemented by local agreement when it is required.

Dynamic DNS updates:
http://www.ietf.org/rfc/rfc3007.txt




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4.1.5 Resolver Service
Providing resolver service to end sites has other considerations. Where resolvers are
provided off-site, any link failure will also break the DNS resolution. As the link is
down, this may not initially seem to be a problem - what good is DNS resolution if the
wide area network is unreachable?

However, there may be reasons why a site still needs DNS resolution for internal
purposes, such as an on-site e- mail server or interactions between local proprietary
networking protocols and the DNS.

In many such cases, some form of resolver service (and also local DNS zone service) is
needed on site. This resolver may simply be configured to resolve local information
only, and forward all other queries off- site, but in the case of link failure this will mean
that local information is always available. Under normal operation, this will prevent
unnecessary DNS requests being passed to the wide area, helping more efficient
operation of both the IP and other networking.

(Note the distinction between resolution on site, where the local server is configured to
interact directly with the Internet, and the forwarding of queries, where the local server
hands off a query to a server on its upstream network. In the first case, the local server
will require external connectivity via NAT, in the latter it does not).

4.1.6 Private and Public Address Space Interactions
In the situation where hosts are reachable at a different address internally than externally
(for example, where private address space is being used with NAT), DNS servers are
required to return different information for internally sourced queries than those sourced
externally. As discussed earlier, this is often referred to as split- view DNS.

The most straightforward solution for this is to run two separate nameserver setups; one
configured to serve internal data and resolve queries from internal hosts. A separate
nameserver configuration handles external queries. Each nameserver setup by default
then returns appropriate information depending upon the source of the query.

Some nameserver software can be configured to conditionally return different
information, depending on the source address of the query.

4.2     E-Mail
Schools require e- mail services, which must interoperate with Internet RFC2822 standard
based e-mail systems. The service may operate other proprietary standards in addition,
but the ability for schools to communicate with each other and external networks using
Internet standard e- mail is vital. E- mail is one of the fundamental applications required
by schools, and it is essential that a robust and resilient service is provided.

This section provides an overview of e- mail services in so far as they relate to network
design; the main considerations being the location of, access to, and responsibility for



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such services. E-mail security issues are also addressed in the Network Security
document.

It is recommended that email services are hosted by Local Authorities or RBCs rather
than schools. As stated in the Network Security document, school management must
recognise that maintaining anti- virus measures requires considerable resource and
determination.

However, if schools choose to operate their own e-mail systems, co-ordination with the
RBC/LA is essential to ensure that these systems can interoperate smoothly with the
RBC/LA supplied e- mail service. The school's mail system should also support
interoperation with other systems using RFC2822 e- mail, even if a proprietary messaging
system is used within the school.

Direct external access to a school's own e-mail servers is not recommended. E- mail
should be accessible via a Web mail interface; if required, using the Internet standard
Post Office Protocol version 3 (POP3) or Internet Message Access Protocol vers ion 4
(IMAP4). See section 4.4 on external access for further information.

As with other content delivery to schools, a filtering system must be available, to help
ensure that inappropriate messages do not reach end user mailboxes. Where a school
operates its own mail server, the school must also maintain such a filtering system if it
does not make use of the RBC/LA provided filtering mechanism.

It is emphasised that if a school chooses to host their own email service then they are
liable for the support, maintenance and security of that service.

References:
RFC2822 Internet e- mail: http://www.ietf.org/rfc/rfc2822.txt
Post Office Protocol version 3: http://www.ietf.org/rfc/rfc1081.txt
Internet Message Access Protocol version 4: http://www.ietf.org/rfc/rfc3501.txt

4.3    Web Services
Web browsing is the prime application requirement for the majority of organisations
connected to the Internet. This section provides an overview of Web services in so far as
they relate to network design; the main considerations being the location of, access to,
and responsibility for such services.

Schools Web browsing requires that inappropriate content can be filtered out, although
the filtering configuration should be flexible enough to allow it to be tailored for different
groups. For example, some content deemed inappropriate in normal circumstances may
be directly relevant to advanced studies in later years of secondary educatio n. The
Network Security document covers content filtering issues in further detail.

Many schools have a requirement to operate their own Web sites, for business and
teaching purposes. Industry best practice typically employs a dedicated server hosting
location, located on a dedicated local network at a service provider's data centre. Space is


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made available to customers on managed servers - the service provider undertakes the
system administration, including operating system upgrades and patches, and the
operation of the web serving software.

Users are assigned individual administrative logins to the servers, allowing them to
directly manipulate the files and scripts making up the Web site, without the significant
responsibility of maintaining the server itself.

The Web server software should support version 1.1 of the HTTP protocol, as specified
in RFC2616. One particular feature of version 1.1 that is not present in the 1.0 standard
is virtual hosting. This allows many web sites to be operated on the same server, yet be
accessible by individual standard school domain names.

In some cases schools may wish to operate their own web server on-site, which is
undesirable. In addition to the issues associated with direct external access into the
RBC/LA and school's networks (see section 4.4), all traffic to and from the web site will
be traversing both the schools access link, and the RBC/LA backbone. If the site is
located at a central hosting facility this extra traffic load is relieved.

Schools may wish to consider operating two web sites; one which is located at the school
and is accessible within the RBC/LA network only and another on a managed server.
When the same data is required to be visible from both servers,
replication/synchronisation techniques could be used so that the data is only uploaded and
edited on one server. For example, a school may nominate the on-site server as the
master, and make changes and additions on this server only. With appropriate file or web
site synchronisation software, the server at the hosting centre would automatically update
itself from the master.

It is most unlikely that there are circumstances in which it makes sense to place web
servers on-site at a school. A well provisioned web hosting location should be able to
offer the same degree of flexibility in operation and maintenance of the web site, and
significant benefits in terms of reducing traffic load on slower links.

HTTP 1.1: http://www.ietf.org/rfc/rfc2616.txt


4.4    External Access
As already noted, schools may request that direct external access to a server on site be
enabled; alternatively, it may be absolutely necessary to enable external access to hosts
on a school's internal network to allow suppliers administrative access to software
services that they provide.

Direct, unauthenticated access to machines on the school's network puts not only that
school's network at a higher risk of security incidents, but may very well put the level of
security for the entire RBC/LA network at risk. Schools should be clear of the level of
responsibility that they are taking on if they create a route for possible unauthorised
intrusions in this manner.


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Better solutions for external access will almost certainly be available, using authenticated
proxy servers or virtual private network (VPN) solutions.

In the case of e- mail, for example, messages to and from the school should be configured
to relay through (and be filtered by) the LBC/RA e- mail system. As already discussed,
the serving of web sites can be provided by a central RBC/LA run server hosting facility
to which the schools have their own direct access from the network at their school.

Other access might be provided to students and teachers through proxy web interfaces to
the school's facilities - for example, products are available to permit access to filestores
via a Web interface. Management access for service suppliers could be provided via a
VPN solution, allowing support staff direct access to their servers inside the school - but
only via a more secure, authenticated link.

Enabling any form of external access will always increase the risk of incidents; carefully
thought out methods of providing the access should be able to keep this risk as low as
possible.

This section is not intended to be an exhaustive review of the issues associated with
external network access. Security issues are covered in more depth in the Network
Security document.

4.5    Location of Network Services
The location of network services within the network topology is an important issue. As
these services require a level of unsolicited, inbound external interaction, best industry
practice dictates that they be logically (and physically if possible) separate from the
network infrastructure providing the basic connectivity.

The majority of service providers locate their DNS servers, e- mail servers, web servers
and other network service devices on separate IP networks - not only from the customer
network, but also from each other. This allows security policies to be tailored for each
service, and in the event of an incident on one of these services networks, the others are
better protected than if they were to share the same IP subnet and/or physical equipment.

It is critical that DNS service is resilient, and that at least one secondary server is
provided, preferably outside the RBC/LEA network, but at least in a separate physical
location. In a network with only a single core location, this server could be
accommodated at an access/aggregation PoP, or perhaps even on-site at a school.

Ideally, all services should be provided in a resilient fashion, perhaps by engineering a
network topology with two nodes hosting duplicate sets of network services.

4.6    Disaster Recovery
It is important to consider what happens when there is a major failure on the network.
This may be anything from the failure of a vital piece of equipment or major node, to the
theft of routers or servers, or the commercial failure of a telecommunications supplier.

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This section suggests some possible disaster scenarios, but by no means covers them all.
Even if it is not feasible (for example, for cost reasons) to have a disaster recovery plan in
place, it is vital to have the plan itself.

Designing a network with duplicated core nodes is a good step towards disaster recovery.
However, the nodes must be in sufficiently geographically distinct places so as to reduce
the risk of common power or telecommunications grid failures affecting them. The loss
of one node will still affect all sites that are only connected to it. If there is a major
disaster that takes days, weeks or even months to fix, arrangements will be needed to
restore service, perhaps by temporarily re-homing links to the other node(s).

Equipment failures are generally covered by maintenance contracts; it is important to
ensure than an appropriate response time is agreed. Failure of equipment causing half the
network to be disconnected clearly cannot be covered by a next business day response
time. Equally, it is vital to check that the response time quoted by a supplier is not just
the time within which they will acknowledge and start working on a maintenance request.

Where it has not been possible to engineer resilience into a network, it may make sense to
hold some degree of spares on-site. For example, anything from holding a spare interface
card to a duplicate router configuration on stand-by where a major portion of the network
relies on a single router. At very remote end sites, it may be advisable to keep a pre-
configured, duplicate router that can be quickly swapped in by local staff.

When spares are held, it is vital that they are checked regularly, to ensure as far as
possible that they are not found to be faulty when needed.

Purchasing a network solution from a single supplier almost always results in cost
savings. However, this means that the network will rely almost exclusively on common
infrastructure. If there is a disastrous failure on that single provider's network, all of the
RBC/LA network will be lost until it is rectified. Purchasing links from a variety of
suppliers reduces the risk of losing an entire network (although suppliers do share cable
routes, so this is not a foolproof guarantee).

Worse, if the single supplier suffers commercial failure, the network will have to be
quickly reprovisioned. Some advance planning for this (hopefully unlikely) event will
undoubtedly be of benefit.

The theft of running equipment seems unlikely, yet it has been known to occur.


5 Support Services
5.1     Technical Support
Schools must be able to report network problems and request assistance with other
networking problems. The RBC/LA should operate a support centre with a single point
of contact for all schools on their network This support centre should be capable of
communicating with both technical and non-technical school staff - smaller primary

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schools are not likely to have highly technical staff on site, yet will still require fast
resolution of network faults and other difficulties.

The support centre should provide fault reporting and resolving services, liaising with
service providers, including the provider of the National Interconnect, and other suppliers
of the RBC/LA network to resolve problems with the network (e.g. link or equipment
failures), and issues or problems with services provided by the RBC/LA such as e-mail or
web. The support centre should also liaise closely with its counterparts in other RBCs.

A flexible approach to providing effective communications of major network events,
such as an outage, must be provided. Local agreements can require the use of messages
on well-known web sites, e- mail, faxes and text messages to keep nominated schools'
network managers and technicians advised of these events. Effective communication of
events with a broad user impact helps keep the user community informed, and as a result
can reduce the call- in load on support staff. This enables more effort to be directed at
problem resolution.

From time to time it may also be necessary for schools to nominate contacts at their
suppliers to deal directly with the RBC/LA support centre. This will most likely be to
resolve network related problems with supplier's servers, or access to servers on the
school site.

The support centre should offer advice and assistance for both wide area network issues,
and also for issues related to the school's internal network where at all possible.
Administrative issues such as those related to DNS data upd ates must always be actioned,
with care to ensure that the requirement is well specified; third parties involved should
also be well briefed. Once the change has been actioned, it must be tested and the result
checked to be correct.

The responsibilities with respect to the technical support, reporting, and repair of faults
on the Interconnect are set out in the Interconnect Agreements:
http://www.ja.net/schoolsbroadband/rbc_agreement.pdf
http://www.ja.net/schoolsbroadband/leacontract.pdf


5.2     Network Monitoring
The RBC/LA support centre should maintain a network monitoring system (NMS),
allowing staff to proactively respond to network outages during working hours as they
occur. The system should be capable of quickly bringing link outages, equipment
failures and other major network problems to the attention of support centre staff.

The NMS, or an alternative dedicated system, should also measure and record traffic and
utilisation levels on links in the network for both reporting and capacity planning.

The NMS should be capable of identifying links that are approaching congestion in real
time. Congestion levels may be simply a product of demand, which requires the adding
of extra capacity, or may be an indication of some form of problem. An unusually high


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amount of traffic on a school's link may be an indication of a widespread virus infection
on the school's PCs, for example.

Increasing error rates on a link indicate a growing problem that will often result in
complete loss of the link in the short term. This information is usually available to
telecommunications suppliers, but is seldom acted upon unless reported by the customer.
The support centre's NMS should be capable of providing notification of such
deteriorating links, to allow staff to report the problem to the supplier before the links
fails.

Where possible (and requested), the support centre should be capable of remotely
monitoring the local networks at schools, including the view of wide area performance
from the perspective of a user at the school. This will particularly aid the analysis and
diagnosis of problems involving smaller schools where dedicated network staff are not
available full- time on site.

More detailed traffic analysis tools are desirable, particularly to identify the different
services and protocols being used on a school's link. Some RBC/LAs have already found
that congestion on links in their networks has been caused by heavy use of applications
such as Internet gaming and radio. By removing access to these services, either
completely or on a time basis (e.g. not in school hours) network performance for users
has been greatly improved.

5.3    Information Dissemination and Staff Development
High-quality technical support at both school and RBC/LA levels is essential to the
success of broadband in schools. The construction of the RBC/LA networks is a complex
undertaking and all those involved are on steep learning curves. Every opportunity
should therefore be taken to size opportunities for staff development.

A major factor in the uptake of network standards will be the dissemination of
information to all involved. RBCs/LAs will need to provide a Web site with a full range
of information including:

      National standards documents
      Service level agreements between schools and the RBC
      Guidance notes

It may also be important to use conferences, meetings and newsletters to draw attention
to this material at both management and technical levels.

The RBC/LA may be required to provide training for end users of the network services it
provides, but not where a school is choosing to operate its own service independently of
the RBC/LA offering.

For example, a school may reasonably expect that the RBC/LA would provide training on
using its Web mail or Web hosting service, or be provided with information on how to
interact with the support centre. However, a school operating its own e- mail server


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should not expect training from the RBC/LA on anything other than how their system
would interoperate with the RBC/LA e- mail relay system.


6 Advanced and Emerging Technologies
Some more advanced technologies are currently emerging, however it is not expected
that these will become requirements for the majority of schools' networking in the near
future. This section notes some of these technologies for reference.

Where local conditions require these or any other additional services, coordination
between the schools, RBC/LA and suppliers is essential. This should help to ensure that
the required services are developed, and are maintained in line with industry standards as
they themselves develop.

6.1    IPv6
The initial driver for IPv6 was the perception that IPv4 address space would soon be
exhausted; this observation was made in the early 1990s. In the intervening time, much
stricter controls on assignment of IPv4 address space, and methods such as IPv4 private
address space have slowed this rate of exhaustion considerably.

IPv6 is not yet widely adopted, and techniques such as private IP address space and NAT
satisfy many organisations' requirements. However, using IPv6 addressing is sometimes
seen as an attractive alternative to the rigorous application process for large amounts of
public IPv4 addresses.

For the moment, though, the vast majority of network resources are only available using
IPv4. Mechanisms to enable IPv6 access to IPv4 service, and vice versa, are not yet
widely deployed and in some cases may not be able to provide a transparent service.

For further information on how the Higher and Further Education communities are
trialling IPv6, see: http://www.ja.net/development/ipv6/.

6.2    IP Multicast
IP multicast is a bandwidth conserving technology that can reduce traffic by transporting
single streams of information across the network backbone to regional and local
distribution points, where the data is replicated for simultaneous delivery to multiple
users. Some applications that can take advantage of multicast include videoconferencing,
video serving and news distribution.

Again, this is seen as an advanced technology, which is not yet required for use on
schools' networks, but for further information on how JANET uses multicast see:
http://www.ja.net/development/multicast/




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The JANET Multicast technical guide, which provides information for sites wishing to
use multicast on JANET is available from:
http://www.ja.net/documents/tg-IPMulticast.pdf

6.3    IP Quality of Service (QoS)
An IP network has traditionally offered a "best-efforts" service, where all IP packets were
treated in the same manner, regardless of application. When congestion occurs on a
network link, any one packet is as likely to be dropped as any other.

With the increasing use of multimedia applications such as videoconferencing and voice
over IP (VoIP), this best-efforts behaviour is undesirable. While a web browsing session
would tolerate packet loss (albeit at a detrimental performance to the user), packet loss on
voice and video can make application useless. Being able to handle such multimedia
packets with a higher priority than others is seen as a useful tool.

Where schools are making heavy use of videoconferencing, VoIP or other delay sensitive
interactive multimedia services, IP QoS may become a requirement, so that traffic for
these services can be prioritised. This is particularly true for networks that are running
close to congestion. However, ultimately, IP QoS is no substitute for the provisioning of
sufficient end to end capacity in a network to support the services that schools require.

IP QoS is still somewhat in its infancy, however, and perfectly acceptable voice and
video connections can be made over a network provisioned with suitable capacity.

The Videoconferencing document provides an overview of IP QoS and classes of service.

For further information on JANET's QoS implementation, see:
http://www.ja.net/development/qos/




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7      References
DfES Standards Fund Guidance
ICT in Schools Standards Fund Grant 2004-05
Guidance for Schools and LEAs
http://www.dfes.gov.uk/ictinschools/funding/

DfES Policy on Connectivity
ICT in Schools Standards Fund Grant 2003-04
NGfL Grant 601a: Information for LEAs and Schools
http://www.dfes.gov.uk/ictinschools/funding/composite.cfm?partid=46

UK Gove rnment’s e-Government Interoperability Frame work (e-GIF)
http://www.govtalk.gov.uk/interoperability/egif.asp.

IETF RFC standards
http://www.ietf.org/rfc.html

ITU standards
http://www.itu.int/ITU-T/publications/recs.html

Private IP address ranges
http://www.ietf.org/rfc/rfc1918.txt

Standard school domain names:
http://www.nic.uk/SecondLevelDomains/AboutSecondLevelDomains/schuk/England/Inf
ormationForTagHoldersAndLeas/InformationForTagHoldersAndLeas.html

DNS standards:
http://www.ietf.org/rfc/rfc1034.txt
http://www.ietf.org/rfc/rfc1035.txt
http://www.ietf.org/rfc/rfc1996.txt
http://www.ietf.org/rfc/rfc2052.txt
http://www.ietf.org/rfc/rfc2136.txt
http://www.ietf.org/rfc/rfc3007.txt

Inte rnet e-mail RFC2822
http://www.ietf.org/rfc/rfc2822.txt

Post Office Protocol version 3
http://www.ietf.org/rfc/rfc1081.txt

Inte rnet Message Access Protocol version 4
http://www.ietf.org/rfc/rfc3501.txt




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HTTP 1.1
http://www.ietf.org/rfc/rfc2616.txt

SNMP
http://www.ietf.org/rfc/rfc3411.txt

JANET IPv6
http://www.ja.net/development/ipv6/

JANET IP M ulticast, Multicast technical guide
http://www.ja.net/development/multicast/
http://www.ja.net/documents/tg-IPMulticast.pdf

JANET Quality of Se rvice
http://www.ja.net/development/qos/

E2BN Products & Practice
http://www.e2bn.net/e2bn/web/e2bn_tng/e2bn_prod_prac/index.htm

UK Broadband Stakeholder Group
http://www.broadbanduk.org

Broadband connectivity choices
http://www.kent.gov.uk/eis

JISC/UKERNA Satellite Trial Results
http://www.ja.net/development/network_access/satellite/trial.html

JANET National User Group Networking Glossary
http://www.jnug.ac.uk/netglossary.html

National Interconnect Technical Specifications
http://www.ja.net/schoolsbroadband/technical_specs.pdf

National Interconnect Agreements
http://www.ja.net/schoolsbroadband/rbc_agreement.pdf
http://www.ja.net/schoolsbroadband/leacontract.pdf

Regional broadband Consortia (RBC)
http://buildingthegrid.becta.org.uk/index.php?locId=143

Network Security
DfES ICT in Schools Network Services Project
UKERNA, March 2004

Videoconfe rencing
DfES ICT in Schools Network Services Project
UKERNA, March 2004

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Appendix A: Network Topology Discussion
Some bodies may choose to contract the operation of their network to a third party
supplier, where the RBC/LA delegates responsibility for the design, engineering and
operation of the network to the third party. This can be thought of as a "cloud" network,
where the schools are provided with a link to the network, but do not necessarily have
any visibility or interest in the design of the network. (Other than that which provides the
required level of service, of course).

Where the RBC/LA chooses to build the network itself, the construction of the backbone
is certainly of interest; this appendix discusses some possible topologies/architectures.
The technologies discussed are by no means an exhaustive list, but reflect those found to
be already in common use on RBC or LA networks.

A.1 Star Networks

In a pure star topology, the backbone consists of a single location (the "hub"), to which
all customer links are directly connected. This topology has the advantage of simplicity,
but if many long distance (expensive) links are involved it may not be cost-effective.

Star topologies can also raise question over resilience. Whilst the failure of any one link
should only cause loss of connectivity to a single site, failures at the hub may cause
serious problems for many, if not all, sites. For example, power failure to the equipment
at the hub could bring down the entire network.




Providing further interlinked hubs improves the physical resiliency of the network, as
failures at individual hubs affects only those sites connected there. However, failure of
inter- hub links could cause network services (such as DNS or e-mail) located at one hub
to be unavailable to sites connected elsewhere.




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This topology now starts to reflect the typical Internet network architecture. Each hub
aggregates customer access links, and interconnects them with the others. This
interconnectivity needs to be engineered in some way; the vast majority of service
providers (including academic networks) do this using IP routing.

Interconnecting aggregation points in a star network can provide a degree of resilience, as
shown below. Alternative routes from the two outlying core nodes to the centre node are
provided via aggregation hubs. This has implications for the equipment located at the
aggregation points, as it now has to be capable of handing the extra traffic load in case of
failure.

Equipment configuration at the aggregation hubs will be more complex. However, as the
overall topology is now a dual-ring solution (see below for ring topology discussion) this
provides a great degree of resiliency. Even failure of both links between the core hubs
will not isolate any part of the network (although performance may degrade if the
network links are not provisioned with sufficient capacity to cope with failure modes).




However, it is still possible to operate a logical star topology where there is more than
one hub, using a technology such as MPLS to carry VLANs from each site to a central

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location. This causes inefficient use of network capacity - traffic between two sites on
the same hub may cross the backbone twice (to the centre and back out again), where in
an IP routed network traffic may simply flow from one port to another on the same
router.

This effect could be particularly undesirable if two sites on the same hub were to hold a
high bit rate point-to-point H.323 video conference, say at 768kbps. In a logical star
network this would almost overload all 2Mbps links between the hub and the central
location. Worse, H.323 video can peak at double the configured bit rate, so the single
videoconference would overload the entire backbone network between the hub and
central point.

On a routed network, this point-to-point video traffic would not leave the local hub,
maybe not even a single router if both sites were connected to the same equipment.


A.2 Ring Networks
The final topology example discussed in the last section can be improved upon by the
addition of a single extra link, to interconnect the hubs on the left and right in the
illustration. This connects the three hubs in a ring, so that any failure of one of the three
backbone links does not necessarily cause loss of connectivity. If direct connectivity
fails, the affected hubs still have the potential to pass traffic between each other, via the
third hub.




The rerouting of traffic is the default behaviour for a dynamically routed IP network, and
can also be engineered for other technologies such as MPLS. Traffic congestion may
well occur, of course, as two remaining links are carrying extra traffic; again, this effect
will be magnified in the case of a logical star network.




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A.3 Resilience

Using a ring topology for the backbone certainly helps to prevent loss of connectivity to
any set of sites; however it is not sufficient simply to implement a ring architecture
without consideration to the underlying physical infrastructure.

Supplier diversity or diverse delivery of circuits is an important factor. If all circuits are
obtained from the same supplier, and delivered over the same path, to the same
equipment rack, a common failure to the supplier's network, the physical path to the local
delivery point or failure of the supplier's on site equipment will take down all circuits at
that location.

In the last topology discussed above, this could mean that both backbone links from the
hub would go down and the hub would be isolated. If all links at that hub were delivered
in the same way, it is arguable that this makes no difference, a s all customer links will go
down too. However, in this case, what is the point of the cost of providing two backbone
links and router interfaces when only marginal resiliency is gained?

If one or more customer links are delivered in some way independently of the backbone
supplier, then more careful specification of the backbone links could have retained wide
area connectivity for those customers.

Where attention has been paid to resiliency in the network design, similar careful
attention should be paid to the procurement of the actual network links.

Similar considerations can also be applied to sites, where it may be desirable to have
more than one connection to the wide area network. In such cases, it is usually more
straightforward to operate an access router (or more) at the local site end, allowing
central control over the interconnectivity.

Formulating a routing plan is critical to the success of resilient configurations. The plan
should detail where particular traffic is expected to go under normal operations, and
consider traffic paths under failure conditions. This helps to adequately provision
network links at the planning stage, and also to troubleshoot when problems occur on the
deployed network.

Where multiple IP routed paths are available to a destination, particularly if there are
links to multiple external networks, an IP routing plan is essential. For example, if a
network has a connection to a service provider and JANET, how should IP traffic be
routed?

External routing protocols such as BGP allow network reachability information to be
exchanged, but require careful configuration of BGP metrics to attempt to influence the
flow of traffic. Unlike internal routing protocols, BGP does not intrinsically have any
knowledge of link capacities or utilisation, and does not have a particularly intelligent
path selection algorithm.



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In the case of two links, the plan is not particularly difficult - the connection to JANET is
likely to be used to exchange traffic with JANET networks only, and the remainder of the
traffic will use the service provider connection. The connection to JANET in this case is
known as a "private peering" - traffic is only exchanged between customers of the two
networks.

However, where multiple service provider links are available for full Internet access, how
should traffic be exchanged? Which service provider link should be used for outbound
traffic for which networks, and (more problematically) which service provider link
should take traffic from the Internet to the local network?

This sort of arrangement is known as "multi- homing", and is one of the hardest IP
networking issues to solve. As such, it is beyond the scope of this document, and it
should simply be noted that extreme care is needed in such situations, and close co-
operation between all networks involved is required.




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Appendix B: Glossary
This glossary explains the terms used in this document. An extensive general networking
glossary can be found at the JANET National User Group Web site:
http://www.jnug.ac.uk/netglossary.html


3G
       Third Generation mobile phone technology; the major UK mobile networks use
       second generation, commonly known as 2G or 2.5G.

802.11b
      Wireless networking standard giving a theoretical data rate of 11Mbps using a
      radio frequency of 2.5GHz

Access Router
     A router, commonly located on a customer site, which provides the connection
     point to the service provider's network.

Address
     In this document refers to an IP address. An IP address is the unique layer
     identifier for a host on the local IP network.

Address Mapping
     The process of translating one IP address to another. A common use is in
     Network Address Translation (see NAT), where an internal IP address is changed
     to an external one, in the IP header, at a network border.

ADSL
       See Asynchronous Digital Subscriber Line.


Asynchronous Digital Subscriber Line
     A common asymmetric configuration of DSL that allows downloads at speeds of
     up to 1.544 Mbps, and uploads at speeds of 128Kbps per second. In theory ADSL
     allows download speeds of up to 9Mbps and upload speeds of up to 640Kbps. See
     DSL and SDSL.

Asynchronous Transfer Mode (ATM)
     An ITU standard for a layer 2 fixed size cell transmission technology.

ATM
       See Asynchronous Transfer Mode




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Best Efforts
      A network service where no packet is treated any differently from any other; no
      guarantees about speed of delivery or even of actual delivery are made. Often
      used in an IP QoS context to refer to the default network service.

Border
     The boundary between one network management domain and another; the
     connection between the RBC and the National Interconnect is the border between
     the RBC and JANET.

BGP
       Border Gateway Protocol. The external routing protocol operated across most, if
       not all, borders between service provider networks. BGP is sometimes used
       between a customer network and a service provider, although in the schools
       networking context this is unlikely to be the case.

Broadband
     A transmission medium capable of supporting a wide range of frequencies. It can
     carry multiple signals by dividing the total capacity of the medium into multiple,
     independent bandwidth channels, where each channel operates only on a specific
     range of frequencies. [Source: RFC1392]

       In a networking context the term means ‘at least 2Mbps in both directions’.

       The term has been adopted in common usage to refer to connections to the
       Internet at speeds of 128Kbps or greater. These may be asymmetric.

       The OECD definition is an Internet connection at a speed greater than 256Kbps.

       The UK Broadband Stakeholder Group definition of broadband is: „Always on
       access, at work, at home or on the move provided by a range of fixed line,
       wireless and satellite technologies to progressively higher bandwidths capable of
       supporting genuinely new and innovative interactive content, applications and
       services, and the delivery of enhanced public services.‟

Caching
      A technique often deployed to make better use of network and/or server capacity
     in content distribution. A local cache server can be deployed to prevent multiple
     copies of the same data traversing the site's upstream access link.

       Clients request data via this local cache server, which is either preconfigured to
       fetch and maintain copies of the content, or to fetch the required data on the first
       client request. As the data is sent over the local network to each client,    this
       greatly reduces the load on the access link.




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Dial-up
       A temporary, as opposed to dedicated, connection between machines established
      over a standard phone line. [Source: RFC1392]

DNS
       See Domain Name System.

Domain Name System
     The basic name-to-address translation mechanism used in the IP environment.
     Used to translate between human- friendly names such as www.ja.net and the
     numeric IP addresses that computers themselves use to communicate. DNS
     information can also be used to direct the operation of some Internet services,
     notably electronic mail. UK schools can have domain names ending in 'sch.uk'.
     DNS is specified in:
     RFC 1034 (STD 13) http://www.ietf.org/rfc/rfc1034.txt
     RFC 1035 http://www.ietf.org/rfc/rfc1035.txt

DSL
       See Digital Subscriber Line.


Digital Subscriber Line
       A technology for transmitting data over conventional copper telephone lines. A
       DSL circuit is much faster than a normal phone connection and must be
       configured to connect two specific locations, similar to a leased. DSL is now a
       popular alternative to Leased Lines and ISDN, being faster than ISDN and less
       costly than traditional Leased Lines. See ADSL and SDSL.

E1, E2, E3
       ITU standard for telecommunications links generally delivered over copper
      wires. E1 refers to a 2Mbps service, E2 8Mbps and E3 34Mbps.

EGP
       See Exterior Gateway Protocol.

Ethernet Hub
      Legacy device for providing Ethernet service. A hub has a number of interfaces
      to which hosts or other network devices are connected so that they may
      interoperate. A more advanced solution is an Ethernet switch.

Ethernet Switch
      Device used in providing an Ethernet network. Ethernet switches generally
      provide better performance, management and security features than an Ethernet
      hub.



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Exterior Gateway Protocol (EGP)
      An IP routing protocol used between backbone networks; usually each backbone
      will be operated by a different organisation.

Frame relay
     ITU communications standard for a layer 2 service using variable length packets
     of data, known as frames.

Forward Mapping
     DNS term referring to the translation of a textual domain name into an IP address.

Gbps
        Gigabits per second, a unit of transmission speed equivalent to 1024 Mbps.

H.320
        Component standard of H.323.

H.323
        The ITU standard for videoconferencing.

Hub
        See Ethernet hub

IANA
        See Internet Assigned Numbers Authority.

IETF
        See Internet Engineering Task Force

Internet Assigned Numbers Authority (IANA)
      The IANA is a body based in the USA which is responsible for maintaining the
      official lists of different numbering schemes in use on the public Internet. Two
      examples of such numbering schemes are IP address allocations and Internet
      service protocol numbers.

Internet Engineering Task Force (IETF)
      The body which develops standards for the Internet and Internet services, which
      are published mainly as RFC documents. Participation in the IETF is open to
      anyone; further information is available at http://www.ietf.org.

IGP
        See interior gateway protocol.




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In-band
      A connection made to a device, such as a router, which uses the network of which
      the device itself is a component. Failure of parts of the network may make in-
      band connections to some devices impossible; out-of-band facilities are generally
      provided to address this problem.

Interior Gateway Protocol (IGP)
       An IP routing protocol designed for use within a single network - for example, the
       backbone of an Internet service provider.

International Telecommunications Union (ITU)
      A telecommunications standards body. The ITU initially was concerned with
      defining standards for basic telecommunications infrastructure; it now also works
      in other areas such as IP videoconferencing.

Internet
      The global public network comprising many interconnected, but independently
      operated, service provider networks.

Internet Protocol
      The communications standard used on the Internet.

Internet Service Provider (ISP)
       An organisation offering connections to the global Internet.

IP
       See Internet Protocol

IPv4
       Internet protocol version 4, the version of IP in mainstream use on the Internet
       today.

IPv6
       Internet protocol version 6, designed as a replacement for IPv4. Not yet in
       common usage.

IP Premium
      IP quality of service (QoS) term for a network service offering priority treatment
      of particular traffic over others.

IP Router
      An intermediate network device which forwards IP packets to the next point along
      the path to their destination. An IP router will usually contain at least two
      interfaces connected to different IP networks.

       The backbone networks that make up the Internet consist of many such devices.



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IP Routing
      The mechanism by which an IP router learns which IP networks are reachable
      over which of its interfaces.

IS-IS
        An internal IP routing protocol.

ISP
        See Internet Service Provider

ITU
        See International Telecommunications Union.

JANET
     See Joint Academic Network.

Joint Academic Network
       The UK academic and research network, interconnecting higher and further
       education institutions and providing them with connectivity to the global Internet.
       JANET also provides the National Schools Interconnect.

Kbps
         Kilobits per second, a unit of transmission speed equivalent to 1024 bits per
        second (bps)

Local Authority
      A UK regional body which may operate its own local network providing service
      directly to schools.

LA
        See Local Authority.

Local Area Network (LAN)
      A network providing service to a small geographical area, such as a single
      building or a campus. LANs are often provisioned using Ethernet technology.

LAN
        See Local Area Network.

Layer 1
       A networking term referring to the physical components of a network such as a
      leased circuit or a device such as an Ethernet hub.

Layer 2
       A networking term referring to the network protocol operated immediately over
      the layer 1 infrastructure. Ethernet or PPP are examples of layer two
      technologies.


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Layer 3
      The protocol operated over the layer 2 network, such as IP.

LAN Extension Service
     Telecommunications service requiring the minimum of extra customer equipment
     or effort to extend a LAN over a wide area point-to-point link. These services are
     usually Ethernet based.

LES
       See LAN Extension Services

Mbps
       Megabits per second, a unit of transmission speed equivalent to 1024kbps.

MPLS
       See Multi-Protocol Label Switching.

Multicast
      A technology allowing any single traffic source to send data to multiple
      destinations. The source sends a single copy of the data, and the network
      replicates the data, where required, to reach all destinations. Multicast makes
      efficient use of bandwidth, but is a complex technology to configure and
      maintain.

Multi-homing
       The practice of obtaining more than one external connection from the local
       network. IP multi- homing is a complex situation which requires careful planning.

Multi-Protocol Label Switching (MPLS)
       MPLS is a technique primarily designed for traffic engineering, and is often
       operated in parallel with IP on network. Where MPLS is used, packets are
       forwarded on the basis of the MPLS label, instead of the destination IP address.

Nameserver
    A network server offering DNS service.

NAT
       See Network Address Translation.

Network Address Translation (NAT)
     A technology for translating IP addresses in the IP packet header. It is often used
     where the IP addressing in use on a network is not globally unique (for example:
     private IP addresses). Using NAT these internal addresses can be automatically
     translated into valid public addresses when communication outside the local
     network is required.




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Open Shortest Path First
     A link state, as opposed to distance vector, routing protocol. It is an Internet
     standard Interior Gateway Protocol defined in RFC1583 and RFC1793.

Optical connection
      Network link made using glass fibre and light instead of copper wire and
      electricity. High speed telecommunications links (typically over 100Mbps) are
      always provided as optical connections.

OSPF
       See Open Shortest Path First.

Out-of-band
      Method of connecting to devices providing a network service without using the
      network itself. Often provided as dial- up connections to network equipment
      management or console ports to enable resetting or reconfiguring of equipment
      isolated by network failure.

Packet
     The unit of data sent across a network. "Packet" a generic term used to describe
     unit of data at all layers of the network, but it is most correctly used to describe
     application data units. See also: datagram, frame. [Source: RFC1392]

Packet Filters
     A tool provided on many routers and switches to control the flow of packets in a
     router. Often used to implement a simple firewall by restricting access over an
     interface to particular IP address ranges and/or services only.
PDH
     Plesiochronous Digital Hierarchy. The standard technology for providing high
     speed telecommunications links, now superseded by SDH.

PPP (Point-to-Point Protocol)
      An IETF standard transmission technology commonly used to transport IP
      packets over network links.

Private Address
      An IP address from a reserved address range, which is never directly from the
      global Internet. Network Address Translation (NAT) is often used in conjunction
      with private addresses to enable access to the Internet.

Private Peering
      Interconnection between two service provider networks using a dedicated link;
      for example, the connection between an RBC and JANET for the National
      Schools Interconnect is a private peering.




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Public Address
      An IP address that is unique on the global Internet. Public addresses are usually
      obtained from a network's Internet Service Provider, which in turn obtains blocks
      of addresses from regional Internet registries.

QoS
       See Quality of Service.

Quality of Service (QoS)
      Term referring to the treatment of traffic on a network. IP QoS is in its infancy,
      however it is being trialled (or used on some networks) to provide differing levels
      of service for different customers or customer traffic. IP QoS is often stated as a
      requirement for real-time voice or video applications, as they are very sensitive to
      packet loss. An IP QoS service providing priority treatment for these types of
      applications can help to reduce packet loss.

RBC
       See Regional Broadband Consortium.

Regional Broadband Consortium
     A body providing network services to schools within a defined region.

Regional Internet Registry (RIR)
     An organisation co-ordinating the assignment of public IP addresses. RIRs
     operate on a largely continental basis; the body providing RIR service to Europe
     is the RIPE NCC, based in Amsterdam.

Reserved Address
     See Private Address.

Resolver Service
     A facility providing general DNS lookup service, usually for a restricted client set
     (for example, hosts on the local network only).

Reverse Mapping
     DNS term for the translation of a numeric IP address to a textual domain name.

RFC (Request For Comment)
     Internet standards document produced by the IETF.

Ring Topology
      Backbone network architecture where backbone devices, such as IP routers, are
      connected in a ring. If one link in the ring fails, the backbone retains full
      connectivity as traffic can flow the opposite way around the ring.




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RIR
       See Regional Internet Registry

Router
     Often used as a generic term for an IP router, however the term may be used to
     refer to a device that is routing other protocols in addition to IP.

SDH
       See Synchronous Digital Hierarchy.

SDSL
       See Symmetric Digital Subscriber Line.

Serial Link
       Point to point link between two devices where data is transmitted one bit at a
       time.

SNMP
       Simple Network Management Protocol. RFC3411-3418.

Star Topology
      Backbone network architecture where the network is based around a small
      number (or even a single) node.

Stateful Firewall
      Security device that can inspect both inbound and outbound packets to and from a
      network, and keep track of connections over time. The device usually allows for
      a more flexible and controlled implementation of a security policy compared to
      packet filters.

STM (STM-1, STM-4, STM-16, STM-64)
     ITU standards for SDH services. STM-1 defines a 155Mbps service, STM-4 622
     Mbps, STM-16 2.5Gbps and STM-64 10Gbps.

SuperJANET
     The national backbone of the JANET network.

Switch
      Ethernet switch.

Synchronous Digital Hierarchy
     SDH is the standard telecommunications technology for providing high speed
     telecommunications links. (See STM)

Symmetric Digital Subscriber Line
    Symmetric DSL (SDSL) can provide up to 2Mbps both ways.
    See DSL and ADSL.


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Traffic Engineering
       Traffic engineering is often used on IP networks to allow IP traffic to take a path
       through the network other than that dictated by IP routing information. This can
       be used to take advantage of less congested links, or perhaps to separate the
       transport of different types of traffic.

       Traffic engineering is commonly understood to imply MPLS, however there are
       other technologies available.

UKERNA
    See United Kingdom Education and Research Networking Association

United Kingdom Education and Research Networking Association
      The organisation responsible managing, operating and developing JANET.

UMTS
       Mobile telephony standard used by 3G networks.

Virtual LAN
       A LAN operated using the same physical infrastructure as one or more other
       LANs. Groups of ports on a switch are configured as part of the VLAN, with the
       connected devices being unaware that the interconnecting network is not
       dedicated to them. VLANs can be extended (or "trunked") across several
       switches, perhaps using LES technologies.

Virtual Private Network
       A client across a public network such as the Internet may appear to be part of a
       private network by encapsulating the private packets inside public packets which
       are routed in the normal way to a device (typically a firewall) on the private
       network which in turn unpacks them and sends them on the private network, a
       process known as „tunnelling‟. There should also be some form of authentication
       and authorisation, and encryption of at least the authentication process and
       preferably data transfers too.

VLAN
       See Virtual LAN

VPN
       See Virtual Private Network




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