Cisco CISCO876-SEC-I-K9 Configuration Guide - Page 167

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 RIP Enhanced IGRP Ideal Topology Metric Routing Updates Suited for topologies with 15 or fewer hops. Hop count. Maximum hop count is 15. Best route is one with lowest hop count. By default, every 30 seconds. You can reconfigure this value and also use triggered extensions to RIP. Suited for large topologies with 16 or more hops to reach a destination. Distance information. Based on a successor, which is a neighboring router that has a least-cost path to a destination that is guaranteed to not be part of a routing loop. Hello packets sent every 5 seconds, as well as incremental updates sent when the state of a destination changes. 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. OL-5332-01 Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide B-3