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.