Notable Issues

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• • • • • What are routers (Ponta) Data Conversion (Adrian) Routing (Albert) Routers (Jordan) Router Architecture (Victor)

Routers vs. Computer
• What is a computer?
– A general purpose machine that takes an input translates the input under software control and gives an output.

• A router is also a computer
– not a “general purpose machine” – Main purpose is to route data

• Today’s networks are large masses of routers • Routers take any form of data such as email, web-browser requests, and file transfers and deliver them to the appropriate destinations. • The internet is a large network of interconnected routers.

Routing in a nutshell
• Routers work by reading the IP address of data packets and determines the correct source and destination for the packet. • The router can also discover the best way to get the packet to its destination.

Routing in a nutshell (cont.)
• Routers take requests from their local users and forward those requests to the appropriate host.

• Routing is the process that allows data to travel from one host to another • Routing is responsible for the making the Internet work.

Without Routers
• Every computer would have to be connected together • Users would need to know
– the address of every website they wanted to visit – All the computers you would need to pass through to get to the destination computer.

Accessing Websites
• You enter a URL address in to your web browser (e.g. Internet Explorer, Netscape Navigator, etc.), e.g, • The browser sends a message to the router • The message notifies that you want to see the information stored at • The process begins

Internet Explorer


Address Conversion
• DNS servers translate the alphanumeric URL,, address to an IP address: • Packets are sent to the routers that read this address

Routing Packets
• Each router examines the packet
– Determines the IP address – Matches the information against its own routing table. – Chooses which port to route it out of

Routing Table
• A two column table • First column identifies each router in the network • Second column lists the router to which each router should send data to

Routing Table
• Router examines packet • If exact match, forwards the message • If there is no match, it runs though table again, looking for a match • If still no match, router sends the packet out of the default next-hop address

Routing Table
• Router sends an ICMP() “host unreachable” or “network unreachable” message back to sender ultimately if no match is found. • Difficult part of router’s job is not how it routes, but how it builds up its table

Routing Table Example
Source Destination Next Hop
A A A A B B B C D E F G B B D B or D C or E C

Routing Packets
This process continues until the request finally reaches

• The routing tables have been keeping track of the path to the destination. • The routing path is now known by the initial router.

Routing Algorithms
• Routing algorithm
– complex set of rules that take into account a variety of factors

• Determines what is the best via routing algorithm • Selects the best path between the source and destination machine

Routing Issues

Flooding the Network
• Early routers were slow • The networks they ran on were equally lowpowered, with little bandwidth • Isolated in that they did not exchange routing tables • As a result routers forwarded data by flooding every path with packets

How can we solve this?
• Backward learning-router remembers the source addresses of all incoming packets and notes the physical interface it came in on • Static Routing
– Rely either on a human or host computer to make these decisions

• Source routing-end hosts place information in every packet they place on the network

Centralized vs. Decentralized

Centralized Routing
• All routing decisions are made by one central computer or router • Typically used in host computers • All computers are connected to the central computer

Decentralized Routing
• All computer or routers in the network make their own routing decisions • In larger networks, routing table is developed by the network manager • In smaller networks, routing table is developed by one individual • Most decentralized routing protocols can automatically adapt to changes in the network configuration

Static vs. Dynamic Routing

Static Routing
• Routing decisions are made in a decentralized manner • When new computers are added to network, they announce their presence • Commonly used in networks that have few routing options that seldom change

Dynamic Routing
• Routing decisions are made in a decentralized manner by individual computers • Used when there are multiple routes through a network • Routes messages over the fastest possible route

Dynamic Routing
• Distance vector dynamic routing
– Routers count the number of hops along a route. – Routers periodically exchange information on the hop count
Router A Router B

Router D

Router C

Dynamic Routing
• Link state dynamic routing
– Rather than knowing a route’s distance, link state routing tries to determine how fast each possible route is – Routers periodically exchange this information to other routers in the network – Preferred over distance vector protocols because they converge quicker

Dynamic Routing-Drawbacks
• Requires more processing by each computer or router in the network • Transmission of routing information wastes network capacity.

Connectionless Routing
• Used when a message can fit into one single packet • Each packet is routed independently
– A router must make a decision for each packet – Used by UDP (User Datagram Protocol) to send short control messages

Connection-Oriented Routing
• Sets up a virtual circuit between the sender and receiver
– Packets from the same message use the same route



Router Types
• • • Home Routers Small Organization and Office Routers High End Routers

Home Routers
• Usually simple • Examples includes: – Linksys, Cable/DSL, 10/100 Ethernet backbone Features: – Voice over IP telephone installed by Netphone.

• 22mbps “Air Plus” is twice as fast as the usual (11-mbps) 802.11b connection
– Utilizes Texas Instruments patented Digital Signal Processing

• Offers 256-bit encryption
– the strongest available

• Deep firewall configuration options.
– Firewall features are easy to implement – Example: Can designate particular computers as WEB servers or FTP servers which are visible to the Internet


Small Organization and Office Routers
• • Slightly larger routers Do little more than home router – These routers enforce rules concerning security for the office network.

• Provides: – Low equipment costs – Dial-in/dial-out – Frame Relay – Lease Line PPP Connection

3-Com Superstack cont.
• Contains: – Three stackable components
• That provides multi-protocol remote access server • Full function WAN router technology for small and medium sized business.

– Offers secure access Authentication

3-Com Superstack cont.
• In addition:
– it can proxy or relay IP address to another central server. – Simplifies network administration – Enhances the mobility of both remote and local users.

High-End Routers
• • • • Largest routers Handle million of packets every second Work to configure the network efficiently Large stand alone systems

Nortel Networks
• High end routers manufacturer • Provides large high performance, scalable routing devices. – Backbone Node and Backbone Concentrator Node

Benefits of the Nortel Networks
• Enhance network performance • High Network availability • Network investment protection

IBM 2210 Nways Multiprotocol
• Provides network solutions for a range of applications • This allows:
– System administrators to build and manage scalable Web Servers. – Superior to Domain Name Servers round robinquerying

Router Architecture

Router Memory
• • • • Flash ROM Cache RAM

Router Memory
• Flash
– Location where the basic boot image is stored.

Router Memory
– Initializes the processor hardware and boots the operating system software. – Runs when the router is powered up or reset

Router Memory
• Cache
– Primary
• Primary cache is closest to the processor core and has the fastest access

– Secondary
• Secondary cache has slower access than primary cache, but faster access than tertiary cache.

– Trietary
• Slowest of all cache but faster than RAM

Router Memory
• RAM Random Access Memory
• Synchronous Dynamic Random-Access Memory • Runs at 133MHz

• Double Data Rate Synchronous Dynamic Random-Access Memory • Runs at 266MHz

• nonvolatile random-access memory
– Uses lithium batteries to maintain its contents when power is removed

Router Memory
• RAM Packaging
• Single In-line Memory Module

• Dual In-line Memory Module

• Small Outline Dual In-line Memory Module.

Router Ports
• Ethernet
– refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard – 10/100/1000 Mbps

– Integrated Service Digital Network
• Communication protocol offered by telephone companies that permits telephone networks to carry data, voice, and other source traffic.

Router Ports
• T3
– Digital WAN carrier facility – Transmits DS-3-formatted data at 44.736 Mbps through the telephone switching network.

• OC-3
– Operates at 155 Mbps – Provides the highest available interface bandwidth for packet-based traffic

Cisco 7200

Cisco 7200

• Two models
– 7204VXR – 7206VXR

Cisco 7204VXR 4 32 20 4 4 2 4 0 4, 4 2 1 16 32 16, 32 32 Up to 4 Up to 8 Up to 8 6 1 6

Cisco 7206VXR

Configurable Slots Ethernet (10BASE-T) Ports Ethernet (10BASE-FL) Ports Fast Ethernet (TX) Ports Fast Ethernet (FX) Ports EtherSwitch Port Adapters 100VG-AnyLAN Ports FDDI (FDX, HDX) Ports ATM Ports (T3, OC-3) Packet over SONET ATM-CES Port Adapters (Data, Voice, Video), Dual-Wide Token Ring (FDX, HDX) Ports Synchronous Serial Ports ISDN BRI Ports (U, S/T) ISDN PRI, Multichannel T1/E1 Ports Multichannel T3 Ports HSSI Ports Packet over T3/E3 Ports (Integrated DSU) IBM Channel Interface Ports (ESCON and Parallel) VPN Acceleration Module

48 30 Up to 6 Up to 6 2 Up to 6 0 Up to 6, 4 2 1 24 48 24, 48 48 Up to 6 Up to 12 Up to 12 6 1

• Modules based

Cisco 7200 Processors
• 4 types of processor units
– – – – NPE 225 NPE 400 NSE-1 NPE-G1

Cisco 7200 Processors
• NPE 225 • NSE-1

Cisco 7200 Processors
• NPE 400 • NPE-G1

Cisco 7200 Memory Configuration
NPE-225 Microprocessor Memory RM5271 262MHz SDRAM DIMM Max: 128 32K Instr. 32KB Data 2MB NSE-1 RM7000 262MHz SDRAM DIMM Max: 256MB 16KB Instr. 16KB Data 256KB 2MB Fixed 512KB 512KB NPE-400 RM7000 350MHz SDRAM SODIMM Max: 512MB 16KB Instr. 16KB Data 256KB Fixed 4MB 512KB 512KB 512KB 16MB 16MB 16MB 16MB NPE-G1 BCM1250 700MHz SDRAM SODIMM Max: 512MB 16KB Instr. 16KB Data 512KB

Primary Cache Secondary Cache Tertiary Cache Boot ROM NVRAM Flash Memory