By default, EIGRP has auto summary feature enabled. Because of this, routes are summarized to classful address at network boundaries in the routing updates.
To better understand the concept of auto-summarization, consider the following example.

Configuring EIGRP 1

EIGRP configuration closely resembles RIP configuration. Only two steps are required:

•    enabling EIGRP by using the router eigrp ASN_NUMBER command
•    telling EIGRP which networks to advertise by using one or more network statements

The first command, router eigrp ASN_NUMBER, enables EIGRP on a router. ASN_NUMBER represents an autonomous system number and has to be the same on all routers running EIGRP, otherwise routers won’t become neighbors. The second command, network SUBNET, enables EIGRP on selected interfaces and specifies which networks will be advertised. By default, the network command takes a classful network number as the parameter.

EIGRP (Enhanced Interior Gateway Routing Protocol) is an advanced distance vector routing protocol. This protocol is an evolution of an earlier Cisco protocol called IGRP, which is now considered obsolete. EIGRP supports classless routing and VLSM, route summarization, incremental updates, load balacing and many other useful features. It is a Cisco propriatery protocol, so all routers in a network that is running EIGRP must be Cisco routers.

Split Horizon

Distance vector protocols are susceptible to routing loops. Split horizon is one of the features of distance vector routing protocols that prevents them. This feature prevents a router from advertising a route back onto the interface from which it was learned.

Configuring RIPv2 is a pretty straightforward process. Only three steps are required:

1. enabling RIP by using the router rip global configuration command

2. instructing the router to use RIPv2 by typing the version 2 command

3. telling RIP which networks to advertise by using one or more network commands

The first two commands are easy to comprehend, but the last command requires a little bit more thought. With the network command you specify which interfaces will participate in the routing process. This command takes a classful network as a parameter and enables RIP on the corresponding interfaces.

RIP (Routing Information Protocol) is one of the oldest distance vector routing protocols. It is usually used in small networks. RIP is very simple to configure and maintain, but lacks some advanced features of routing protocols like OSPF or EIGRP. Two versions of the protocol exists: version 1 and version 2. Both versions use hop count as a metric and have the administrative distance of 120. RIP version 2 is capable of advertising subnet masks and uses multicast to send routing updates, while version 1 doesn’t advertises subnet masks and uses broadcast for updates. Version 2 is backwards compatible with version 1.