Cisco Systems C819GUK9 manual Routing Protocol Options, Ideal Topology, Metric, Routing Updates

Appendix B Concepts

Routing Protocol Options

IP is a connectionless protocol, which means that IP does not exchange control information (called a handshake) to establish an end-to-end connection before transmitting data. In contrast, a connection-oriented protocol exchanges control information with the remote computer to verify that it is ready to receive data before sending it. When the handshaking is successful, the computers have established a connection. IP relies on protocols in other layers to establish the connection if connection-oriented services are required.

Internet Packet Exchange (IPX) exchanges routing information using Routing Information Protocol (RIP), a dynamic distance-vector routing protocol. RIP is described in more detail in the following sections.

Routing Protocol Options

Routing protocols include the following:

•Routing Information Protocol (RIP)

•Enhanced Interior Gateway Routing Protocol (Enhanced IGRP) RIP and Enhanced IGRP differ in several ways, as shown in Table B-1.

Table B-1	RIP and Enhanced IGRP Comparison
Protocol	Ideal Topology	Metric	Routing Updates
RIP	Suited for topologies with	Hop count. Maximum hop	By default, every 30 seconds.
	15 or fewer hops.	count is 15. Best route is one	You can reconfigure this value
		with lowest hop count.	and also use triggered
			extensions to RIP.
Enhanced	Suited for large topologies	Distance information. Based	Hello packets sent every
IGRP	with 16 or more hops to	on a successor, which is a	5 seconds, as well as
	reach a destination.	neighboring router that has a	incremental updates sent
		least-cost path to a	when the state of a destination
		destination that is	changes.
		guaranteed to not be part of
		a routing loop.

RIP

RIP is an associated protocol for IP and is widely used for routing protocol traffic over the Internet. RIP is a distance-vector routing protocol, which means that it uses distance (hop count) as its metric for route selection. Hop count is the number of routers that a packet must traverse to reach its destination. For example, if a particular route has a hop count of 2, then a packet must traverse two routers to reach its destination.

By default, RIP routing updates are broadcast every 30 seconds. You can reconfigure the interval at which the routing updates are broadcast. You can also configure triggered extensions to RIP so that routing updates are sent only when the routing database is updated. For more information on triggered extensions to RIP, see the Cisco IOS Release 12.3 documentation set.

Cisco 860 Series, Cisco 880 Series, and Cisco 890 Series Integrated Services Routers Software Configuration Guide

B-2 OL-18906-02