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Routing Information Protocol RIP

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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Routing Information Protocol RIP

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

  2. 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

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 • Although superseded by more complex algorithms, its simplicity means is still found widely in smaller autonomous systems.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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).

  9. 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.

  10. 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

  11. RIP • Stephen Webster • Gino Rigitano • Telewest Communications • 0131 539 0002 Telewest Communications Group

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