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					Network design

  WAN topology
    Topic 5
•   Enterprise topology
•   Functions and components
•   Security
•   Design goals
•   Physical standards
•   Topologies
•   WAN link types
   Enterprise Composite Network Model
• A hierarchal and scalable blue-print for network designers
• Enterprise campus
   – The elements for network operation within one campus (building)
   – Designed to provide high availability, scalability, and flexibility
   – Includes a campus backbone, a server farm, building access and building
     distribution modules and a network management module
• Enterprise edge
   – Efficient and secure communication between the enterprise campus and
     remote locations, business partners, mobile users, and the Internet
   – Aggregates connectivity, provides traffic filtering and inspection and
     routing to the enterprise campus
   – Includes WAN, VPN, internet access, and e-commerce modules
• Service provider edge
   – Enables communication with other networks
   – Uses different WAN technologies and Internet service providers (ISPs)
Enterprise Composite Network Model
                             Service Providers
•   Tier 1 provider
     –   National or international backbone with at least DS-3, OC-3 to OC-48 connectivity
     –   All its routes from bilateral peering arrangements
     –   24/7 network operations center
     –   Customers are primarily other providers, but it may support a large enterprise also
•   Tier 2 Provider
     –   Regional or national presence
     –   High bandwidth backbones and 24/7 operations
     –   Buys transit (discounted) from a Tier 1 provider for traffic that goes outside the region
     –   Gets all its regional routes through peering arrangements.
•   Tier 3 Provider
     – Typically a regional provider for a small or medium-sized region
     – Buys transit from multiple upstream providers
     – Runs a default-free routing table
•   Tier 4 and Tier 5 Providers
     – Metropolitan provider multi-homed to two regional providers
     – Small, single-homed provider that connects end users via dialup, cable modem, or wireless
                Enterprise edge module
•   Edge distribution
     – Interface to the enterprise network
     – Web security appliances and Intrusion Prevention appliances
•   E-commerce
     – DMZ security zones with internet facing servers, network services such as DNS, FTP
        and NTP, email, websites and web portal
     – Separates internal and external services such as DNS, intranet and collaboration
•   Internet connectivity
     – Safe and secure access to internet for corporate users, and remote users
•   Remote access VPN
     – Corporate access to remote users such as tele-workers and mobile workers
•   WAN
     – Wan networks such as Frame Relay and ATM to other sites
     – Site-to-site VPNs for branch and partner sites
     – Protection services such as Intrusion Protection services

• Inner switch
   – Provide connectivity between core and campus VLANs and firewall
• Firewall
   – Stateful access control and deep packet inspection
   – Controlling user’s internet bound traffic
   – Protecting public services in DMZ
• Outer switches
   – Provides connectivity between the firewall and the edge router
• Edge routers
   – Route traffic from enterprise to the internet via one or more ISPs
   – Security such as ACLs and uRPF
• Remote access appliances
   – Terminate remote-access VPNs such as SSL and Ipsec VPNs
         Design goals for the edge
• Availability
• Eliminate any single point of failure on the network
   – Redundancy
• High availability for internet, extranet, and virtual private
  network (VPN) with redundant interfaces, standby devices,
  redundant links and devices
• Reliability by duplicating any required component whose
  failure could disable critical applications – a channel service
  unit (CSU), a power supply, a WAN trunk, internet
   – Affordability
• Trade-offs may be required
        Design goals for the edge
• Backup paths
   – How much capacity does the backup path support?
   – How quickly will the network begin to use the backup path?
   – Common for a backup path to have less capacity than a
     primary path and use different technologies
   – Automatic failover is necessary for mission-critical
   – What about the cable to the ISP – often the weakest link
• Multi-homing the internet connection
   – Providing an enterprise network with more than one entry
     into the Internet.
• Circuit diversity
   – Different carriers sometimes use the same facilities
   – Ensure that your backup really is a backup
         Design goals for the edge
• Management
  – Configurations
  – Monitor traffic flows
  – Monitor protocol and process efficiency
  – Security baselines
     •   Device access
     •   Routing security
     •   Device resilience
     •   Policy enforcement
            Designing process
• What are the business and technical goals for
  the Enterprise Edge?
  – Who are the user communities?
  – What is the health of the existing network?
  – Where are the traffic flows?
• What technologies?
• What topology?
• What link type?
       Security and remote access
• Business and technical goals
   – Confidentiality and privacy
   – Integrity
   – Availability
• Security technologies
   – Security zones, ACLs and network address translation
   – Access control
       • AAA services
       • Auditing
   – Protection
       • Application inspection
       • Monitoring and intrusion protection
   – Privacy
       • Encryption
• Remote access
   – Remote access VPNS, SSL and Ipsec VPNS
   – Site-to-site VPNS
                         WAN topologies
•   Full mesh
     – Every router is connected to every other router for complete redundancy
     – Good performance because there is just a single link delay between any two sites
     – The number of links in a full-mesh topology is
           • (N * (N – 1)) / 2
     – Expensive to deploy and maintain, hard to optimize, troubleshoot, and upgrade
     – Scalability limits for groups of routers that broadcast routing updates or service
         advertisements (20% broadcast rule)
•   Partial mesh
     – Not every router is connected to every other router
     – Compromise solution
           • Partial redundancy
           • Less cost
           • Less performance as some destinations might require traversing intermediate
•   Hub and spoke (Star)
     – Common hierarchical design
     – Destinations are reached via the ‘hub’
•   Peer
     – No redundancy, least expensive, easiest setup
    Choosing a WAN link connection
• What is the purpose of the WAN?
• What is the geographic scope?
• What are the traffic requirements? Type, volume, quality
  and security
• Should the WAN use a private or public infrastructure?
• For a private WAN, should it be dedicated or switched?
• For a public WAN, what type of VPN access do you need?
• Which connection options are available locally?
• What is the cost of the available connection options?
   WAN link connection methods
• Private
  – Dedicated
     • Leased lines Point-to-Point and Point-to-Multipoint PPP HDLC
  – Switched
     • Circuit Switched, PSTN, ISDN
     • Packet Switched, Frame Relay, X.25, ATM (cells)
• Public
  – Internet
     • DSL, cable, broadband wireless
     • Satellite
     • Metro Ethernet
                       Leased lines
• Permanent dedicated connections leased from carrier
   –   T1   1.544 Mb/s
   –   T3   44.736 Mb/s
   –   E1   2.048 Mb/s (Australia)
   –   E3   34.064 Mb/s (Australia)
• A router serial port is required for each leased line
• A CSU/DSU and the actual circuit from the service provider
  are also required.
   – CSU/DSU is a Channel Service Unit/Data Service Unit that
     terminates T1/E1 carrier lines
• Lower latency and jitter
• No call setup required
                    Public networks
    – Always-on connection technology that uses existing PSTN infrastructure
      and DSL access multiplexer (DSLAM) at the provider location
    – Varying data rates of up to 8.192 Mb/s and distance limitations
• Cable
    – Always-on connection that uses existing cable TV infrastructure
    – Bandwidth shared by users
• Broadband wireless – WiMax
    – High-speed broadband service over metro distances for many users
    – Provides broad coverage like a cell phone network
• Satellite
    – Rural users, upload speed is about one-tenth of download speed
    – Satellite dish, two modems (uplink and downlink), and coaxial cables
• Metro Ethernet
    – Reduced expenses and administration
    – Easy integration with existing networks
                  Circuit switching
• Establishes a circuit between hosts before communication
  can start
• Initial very fast call setup to establish a dedicated circuit or
  path which cannot be used by others until call tear down
   – Time-division multiplexed (TDM) digital signals
   – Uses 64 kb/s bearer channels (B) for carrying voice or data and a
     signaling, delta channel (D) for call setup and call management
   – Basic Rate Interface (BRI)-ISDN is intended for the home and
     small enterprise and provides two 64 kb/s B channels and a 16
     kb/s D channel
   – Primary Rate Interface (PRI)-ISDN provides 30 B channels and
     one D channel, for an E1 link of 2.048 Mb/s
• ISDN links are used by enterprises as an extra capacity and
  backup link
                 Packet switching
• Packets are routed individually and can follow different
  paths to destination and arrive out of order
• Connection oriented packet switching verifies the
  existence of the destination with a 3-way handshake
• Frame Relay
   – Permanent and shared connectivity for voice and data
     traffic using virtual circuits (up to 4 Mbp/s)
   – Frame Relay is ideal for connecting enterprise LANs
• Asynchronous Transfer Mode (ATM)
   – Small, fixed-length cells carrying data, voice and video
     traffic over private and public networks
    Physical WAN serial standards
• Standards to define how to transmit and receive
  –   EIA/TIA-232
  –   EIA/TIA-449
  –   EIA-530
  –   High-Speed Serial Interface (HSSI)
  –   V.24
  –   V.35
  –   X.25
  –   X.21
  –   G.703
•   Enterprise topology
•   Functions and components
•   Security
•   Design goals
•   Physical standards
•   Topologies
•   WAN link types

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