Cisco Systems OL-6426-02 manual PPP Authentication Protocols, Enhanced Igrp, Rip

Appendix B Concepts

PPP Authentication Protocols

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 when
		least-cost path to a	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.

Enhanced IGRP

Enhanced IGRP is an advanced Cisco proprietary distance-vector and link state routing protocol, which means it uses a metric more sophisticated than distance (hop count) for route selection. Enhanced IGRP uses a metric based on a successor, which is a neighboring router that has a least-cost path to a destination that is guaranteed not to be part of a routing loop. If a successor for a particular destination does not exist but neighbors advertise the destination, the router must recompute a route.

Each router running Enhanced IGRP sends hello packets every 5 seconds to inform neighboring routers that it is functioning. If a particular router does not send a hello packet within a prescribed period, Enhanced IGRP assumes that the state of a destination has changed and sends an incremental update.

Because Enhanced IGRP supports IP, you can use one routing protocol for multiprotocol network environments, minimizing the size of the routing tables and the amount of routing information.

PPP Authentication Protocols

The Point-to-Point Protocol (PPP) encapsulates network layer protocol information over point-to-point links. PPP originally emerged as an encapsulation protocol for transporting IP traffic over point-to-point links. PPP also established a standard for the assignment and management of IP addresses, asynchronous

Cisco 1800 Series Integrated Services Routers (Fixed) Software Configuration Guide

OL-6426-02 B-3