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Routing protocols

Routing protocols
6.3.3
This page will give some examples of routing protocols and how they are used.
At the Internet layer of the TCP/IP suite of protocols, a router can use an IP routing protocol to accomplish routing through the implementation of a specific routing algorithm. Examples of IP routing protocols include the following:
  • RIP - a distance vector interior routing protocol
  • IGRP - the Cisco distance vector interior routing protocol
  • OSPF - a link-state interior routing protocol
  • EIGRP - the advanced Cisco distance vector interior routing protocol
  • BGP - a distance vector exterior routing protocol
RIP was originally specified in RFC 1058. Its key characteristics include the following:
  • It is a distance vector routing protocol.
  • Hop count is used as the metric for path selection.
  • If the hop count is greater than 15, the packet is discarded.
  • Routing updates are broadcast every 30 seconds, by default.
IGRP is a proprietary protocol developed by Cisco. Some of the IGRP key design characteristics are as follows:
  • It is a distance vector routing protocol.
  • Bandwidth, load, delay and reliability are used to create a composite metric.
  • Routing updates are broadcast every 90 seconds, by default.
OSPF is a nonproprietary link-state routing protocol.
  • It is a link-state routing protocol.
  • It is an open standard routing protocol described in RFC 2328.
  • The SPF algorithm is used to calculate the lowest cost to a destination.
  • Routing updates are flooded as topology changes occur.
EIGRP is a Cisco proprietary enhanced distance vector routing protocol. The key characteristics of EIGRP are as follows:
  • It is an enhanced distance vector routing protocol.
  • It uses unequal cost load balancing.
  • It uses a combination of distance vector and link-state features.
  • It uses Diffused Update Algorithm (DUAL) to calculate the shortest path.
  • Routing updates are multicast using 224.0.0.10 triggered by topology changes.
Border Gateway Protocol (BGP) is an exterior routing protocol. The key characteristics of BGP are as follows:
  • It is a distance vector exterior routing protocol.
  • It is used between ISPs or ISPs and clients.
  • It is used to route Internet traffic between autonomous systems.

The next page will discuss interior and exterior routing protocols.

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