EIGRP Updates

wat08

"EIGRP uses EIGRP update messages to send topology information to neighbors. These Update messages can be sent to multicast IP address 224.0.0.10 if the sending router needs to update multiple routers on the same subnet; otherwise, the updates are sent to the unicast IP address of the particular neighbor. (Hello messages are always sent to the 224.0.0.10 multicast address.)"

CCNA ICND2 Official Exam Certification Guide, Wendell Odom, PG #381


If a neighbor relationship can only be formed by routers on the same subnet, then why would you send update messages to a router off the subnet? Why is a router off the subnet referred to as a neighbor in this context?

networker050184

You are not understanding what this is saying. EIGRP sends the updates to the multicast address on multiaccess networks such as ethernet. On a point to point link it sends the unicast as there is only one neighbor and no need for a multicast.

wat08

Got it. Thanks

wat08

Just another question about EIGRP:

Why does Cisco claim this to be a hybrid protocol when it functions solely as a distance vector protocol? The fact that it uses load, bandwidth, delay, etc. explains the "advanced" in "advanced distance vector", but where do the link-state characteristics come in?

kryolla

link states characteristics are hellos and forms adjacencies. Distance vector means it only knows about the routes it neighbors tell him.

Plazma

It referes to the fact EIGRP does not send it's whole routing table over.. which is what classifies a Distance Vector protocol.

wat08

Yes I know, but "hybrid protocol" implies there are also link-state characteristics. I hate wikipedia but I think this is the explanation I was looking for:

http://en.wikipedia.org/wiki/EIGRP#EIGRP_classification_as_a_distance-vector

tech-airman

wat08,

wat08 wrote:

Just another question about EIGRP:

Why does Cisco claim this to be a hybrid protocol when it functions solely as a distance vector protocol?

There is your misunderstanding about EIGRP. What are the features of a pure distance vector routing protocol?

wat08 wrote:

The fact that it uses load, bandwidth, delay, etc. explains the "advanced" in "advanced distance vector", but where do the link-state characteristics come in?

According to Cisco...

Cisco Systems, Inc. wrote:

Link-State Versus Distance Vector

Link-state algorithms (also known as shortest path first algorithms) flood routing information to all nodes in the internetwork. Each router, however, sends only the portion of the routing table that describes the state of its own links. In link-state algorithms, each router builds a picture of the entire network in its routing tables. Distance vector algorithms (also known as Bellman-Ford algorithms) call for each router to send all or some portion of its routing table, but only to its neighbors. In essence, link-state algorithms send small updates everywhere, while distance vector algorithms send larger updates only to neighboring routers. Distance vector algorithms know only about their neighbors.

Source: Internetworking Technology Handbook - Routing Basics - http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Routing-Basics.html#wp1020646

iworms

Well don't dwell on the terminology/marketing terms. Some people call it hybrid, some people don't like to call it hybrid, and some people resent Cisco for calling it hybrid. The important thing for us is to know what distance vector and link state protocols do and what EIGRP does.

tech-airman

iworms wrote:

Well don't dwell on the terminology/marketing terms. Some people call it hybrid, some people don't like to call it hybrid, and some people resent Cisco for calling it hybrid. The important thing for us is to know what distance vector and link state protocols do and what EIGRP does.

iworms,

So in your technical opinion, as opposed to using marketing terms, what type of routing protocol would you call EIGRP with respect to distance vector or link state protocols?