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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter1 Product Overview
Layer 3 Software Features
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.
Note Layer 3 switching does not support the Next Hop Resolution Protocol (NHRP).

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 cla ssless interdomain routing
(CIDR). CIDR lets you reduce the size of your routing tables by crea ting 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
Multicast Services
Multicast services save bandwidth by forcing the network to replicate packets only when necessary and
by allowing hosts to join and leave groups dynamically. The following multicast services are supported:
•Cisco Group Management Protocol (CGMP) server—CGMP server manages multicast traffic.
Multicast traffic is forwarded only to ports with attached hosts that request the multicast traffic.
•Internet Group Management Protocol (IGMP) snooping—IGMP snooping manages multicast
traffic. The switch software examines IP multicast packets and forwards packets bas ed on their
content. Multicast traffic is forwarded only to ports with attached hosts that request multicast traffic.
Support for IGMPv3 provides constrained flooding of multicast traffic in the presence of IGMPv3
hosts or routers. IGMPv3 snooping listens to IGMPv3 query and membership report messages to
maintain host-to-multicast group associations. It enables a switch to propagate multicast data only
to ports that need it. IGMPv3 snooping is fully interoperable with IGMPv1 and IGMPv2.
Explicit Host Tracking (EHT) is an extension to IGMPv3 snooping. EHT ena bles immediate leave
operations on a per-port basis. EHT can be used to track per host membership information or to
gather statistics about all IGMPv3 group members.
For information on configuring IGMP snooping, see Chapter 17, “ Configuring IGMP Snooping and
Filtering.”