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Routing Information Protocol RIP - PowerPoint PPT Presentation

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Cisco CCNA student presentation @ Napier University. Routing Information Protocol RIP. Why is a Routing Protocol needed? Purpose of Routing information Which route? Metrics Routing tables RIP datagram and RIP port Questions. Why is a routing protocol needed?.

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Cisco CCNA student presentation @ Napier University.

Routing Information ProtocolRIP

Why is a Routing Protocol needed?

Purpose of Routing information

Which route?


Routing tables

RIP datagram and RIP port


Telewest Communications Group

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Why is a routing protocol needed?

  • Early requirements to exchanges data between computers over interconnected networks.

  • Routing entities had to make a judgement on which path to route traffic to destination.

Telewest Communications Group

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Background to RIP

  • RIP dates back to 1969, the early networking days and ARPNET when Xerox and Berkley’s Unix implemented it broadly similar protocols.

  • RIP distributed through ‘route d’ application, included in early Unix O.S.

  • RIP uses a single class of routing algorithm known as distance vector - based on a simple hop count algorithm (derived from Bellman’s equation).

  • Although superseded by more complex algorithms, its simplicity means is still found widely in smaller autonomous systems.

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Purpose of Routing Protocol

  • The purpose of RoutING protocols is to supply information needed to do routing of datagrams from router to router.

  • RIP intended for use in IP based network environment.

  • Operating at layer 3 of OSI (Network)

  • RIP makes no formal distinction between networks and hosts.

  • Routers typically provide a gateway for datagrames to leave one network or AS and be forwarded onward to another network.

  • Routers therefore, have to make decisions if there is a choice of forwarding path on offer.

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Which way?

  • A path must be found between the source and destination.

  • Without a direction to follow packet would have to randomly circulate the whole internetwork looking for its destination.

  • If the networks are not adjacent then the path will be through several routers.

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Routing metrics

  • Routing entities keep a database (look up table) of basic information based on numeric result s (metric) of an algorithm to forward a datagram onward to its next destination.

  • Each entity participating in routing decisions sends update messages to its neighbour.

  • In order to provide complete network routing information every router within the AS must participate in the protocol.

  • Each router has a lookup table which contains one entry for every destination that is reachable.

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How does a metric work?

  • Metrics are the result of a formula based on a choice of measurement criteria.

    Example, travel cost by taxi:

    £10 to go by taxi from Edinburgh to Livingston. (P1)

    £25 to go from Livingston to Glasgow (P2)

    £15 to go from Edinburgh to Falkirk (P3)

    £30 to go from Falkirk to Glasgow (P4)

    Cost (Edinburgh, Glasgow) = [P1+P2] = £35

    also/or [P3+P4] = £45

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What is in a RIP routing table?

  • Address - IP address (IPv4) of host or network destination.

  • Router - First router along the route to destination.

  • Interface - The physical network which must be used to reach the next router.

  • Metric - A number indicating the distance to the destination. This number is the sum of the ‘costs’ that have to be transversed to get to the destination.

  • Timers - Time since entry was last updated and others.

  • Flags - Various flags to indicate status of various adjacent routers (for example).

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Other entries in the routing table

  • The entries for directly connected networks typically have a value of 1 (a simple hop count).

  • Initially subnet masks were not included in RIP protocol implementations, but were included later to support feature extensions and to identify different subnets within local and distant networks.

  • Administrators may also add static routes for example, which are outside the scope of the routing system.

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The RIP datagram

  • RIP is a UDP-based protocol.

  • Small regular messages, no need for windowing, handshaking or re-transmission.

  • Frames received and transmitted on UDP port number 520 (Rip 1&2)

  • 1 - 25 RIP routing entries RTEs.

Telewest Communications Group

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  • Stephen Webster

  • Gino Rigitano

  • Telewest Communications

  • 0131 539 0002

Telewest Communications Group