Enhanced Interior Gateway Routing Protocol

Now an open standard. It used to be a Cisco proprietary protocol, but they made an RFC for it. Now EIGRP can be used on many devices, not just Cisco. However, if you use EIGRP on Cisco products, you'll probably have access to more features, and more ways to tweak it.

What is EIGRP?

EIGRP is a hybrid interior gateway protocol. It has characteristics of both Link-State and Distance Vector.

• Link State: Has a full network topology. You can see what sits behind the other routers your sharing information with.
• Distance Vector: Routers only share info about their networks, but you don't have full topology visibility beyond your own network.

EIGRP identifies the next hop very differently compared to other routing protocols.

RIPv2 only uses hop count. How many hops between routers does it take to get to the destination?
OSPF calculates the fastest bandwidth and calls it "cost." The faster the bandwidth, the lower the cost.

EIGRP uses several different variables and combines it into one. It's called distance. It also supports manual and automatic summarization and MD5 authentication.

EIGRP :: Packet Types

Remember this for the test: Most packets sent to the multicast address 224.0.0.10

EIGRP has packets called "Hello Packets". They're used to build new neighbor relationships, and to maintain them. You're not going to send any routes until hello packets are exchanged. Between those packets, there are some parameters that need to match before you can begin sharing routes. You will continue to periodically send hello packets between routers to ensure the connections are still alive.

Update packets carry routing updates. This can be new routes, changed routes, or routes that have gone down. Initially this is Unicast. From that point on, any new things are being sent via multicast (224.0.0.10).