EIGRP (Enhanced Interior Gateway Routing Protocol) is an advanced distance-vector routing protocol used on computer networks to automate routing decisions and configuration on a router to share routes with other routers within the same autonomous system. EIGRP, unlike the routing protocol RIP, only sends incremental updates, reducing the workload on the router and the amount of data that needs to be transmitted. The EIGRP protocol was designed by Cisco as a proprietary protocol, available only on Cisco routers. EIGRP replaced the Interior Gateway Routing Protocol (IGRP) in 1993.
EIGRP supports some of the following important features:
- It supports a Classless Inter-Domain Routing (CIDR) and variable length subnet masking.
- It supports load balancing on parallel links between the sites.
- EIGRP employs ability to use different authentication passwords at different times.
- It supports MD5 and SHA-2 authentication between two routers.
- Rather than sending the entire routing table when a route is changed, EIGRP sends only the topology changes.
- EIGRP propagates routing changes to neighboring routers if any changes have occurred after periodically checking the available route.
- It has got backwards compatibility with the IGRP routing protocol.
Setting up an EIGRP on a Cisco IOS router for a private network involves some basic steps in the router. For eample if 0.0.15.255 wildcard is the bitwise complement of the subnet mask 255.255.240.0.,to setup an EIGRP, we put on the following commnds:
Router# configure terminal
Router(config)# router eigrp 1
Router(config-router)# network 10.201.96.0 0.0.15.255
Router(config-router)# no auto-summary
Its simple configuration steps gives EIGRP the biggest advantage over other highly scalable routing protocols:
– The first step involves gaining access to the Cisco device and accessing global configuration mode.
– To configure EIGRP, the first step involves creating an EIGRP routing instance which is done with the command ‘router eigrp autonomous-system-number’. It is very important to note that the EIGRP autonomous system number is important because only neighbors with matching autonomous system numbers can communicate using EIGRP.
– The next part requires knowledge of the networks that will be advertised from the router. The command used for this is ‘network network’. For example, if an interface exists in the router using the IP network 192.168.1.0 with any mask, then it will now be advertised with EIGRP.
– EIGRP has the summarization capabilities including automatic summarization which is enabled by default. It means if no other interface is configured on the router using the 192.168.1.0 network then a summary route will be advertised in place of the more specific route. To clearify the concept let’s assume that a single interface on a router is configured with the IP address 192.168.1.129 and is using the /25 (255.255.255.128). Then the IP range from 192.168.1.128 through 192.168.1.255 is included in the subnet connected off this interface. EIGRP will advertise the 192.168.1.0/24 network, not the 192.168.1.128/25 network if no other interface is configured on this router . If this activity is unwanted then EIGRP’s automatic summarization must be disabled using the command ‘no auto-summary’.
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