Cisco 4500M Software Manual page 36

Layer 3 Software Features
IGRP
The Interior Gateway Routing Protocol (IGRP) is a robust distance-vector Interior Gateway Protocol
(IGP) developed by Cisco to provide for routing within an autonomous system (AS). Distance vector
routing protocols request that a switch send all or a portion of its routing table data in a routing update
message at regular intervals to each of its neighboring routers. As routing information proliferates
through the network, routers can calculate distances to all nodes within the internetwork. IGRP uses a
combination of metrics: internetwork delay, bandwidth, reliability, and load are all factored into the
routing decision.
EIGRP
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a version of IGRP that combines the
advantages of link-state protocols with distance-vector protocols. EIGRP incorporates the Diffusing
Update Algorithm (DUAL). EIGRP includes fast convergence, variable-length subnet masks, partially
bounded updates, and multiple network-layer support. When a network topology change occurs, EIGRP
checks its topology table for a suitable new route to the destination. If such a route exists in the table,
EIGRP updates the routing table instantly. You can use the fast convergence and partial updates that
EIGRP provides to route Internetwork Packet Exchange (IPX) packets.
EIGRP saves bandwidth by sending routing updates only when routing information changes. The
updates contain information only about the link that changed, not the entire routing table. EIGRP also
takes into consideration the available bandwidth when determining the rate at which it transmits updates.
Layer 3 switching does not support the Next Hop Resolution Protocol (NHRP).
Note
BGP
The Border Gateway Protocol (BGP) is an exterior gateway protocol that allows you to set up an
interdomain routing system to automatically guarantee the loop-free exchange of routing information
between autonomous systems. In BGP, each route consists of a network number, a list of autonomous
systems that information has passed through (called the autonomous system path), and a list of other path
attributes.
The Catalyst 4500 series switch supports BGP version 4, including classless interdomain routing
(CIDR). CIDR lets you reduce the size of your routing tables by creating aggregate routes, resulting in
supernets. CIDR eliminates the concept of network classes within BGP and supports the advertising of
IP prefixes. CIDR routes can be carried by OSPF, EIGRP, and RIP.
For BGP configuration information, refer to the chapter "Configuring BGP" in the Cisco IOS IP and IP
Routing Configuration Guide at the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/ip_c/ipcprt2/1cdbgp.htm
For a complete description of the BGP commands, refer to the chapter "BGP Commands" in the
Cisco IOS IP and IP Routing Command Reference at the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/ip_r/iprprt2/1rdbgp.htm
Software Configuration Guide—Release 12.2(25)EW
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Chapter 1 Product Overview
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