Tuesday, July 22, 2008

EIGRP is a DV protocol, and the secondary IP in the routing protocols ..


This articles is written to declare somethings regarding EIGRP and a hidden trick in every routing protocol:


It is common to say EIGRP is a hybrid routing protocol, BUT, this is a common mistake.
In fact, EIGRP is a distance vector routing protocol, well, at least it has the split-horizon feature. Furthermore, EIGRP contains all the distance vector features, the big BUT here is: it is an enhanced Distance Vector protocol, so, it does not have the negative features other DV protocols have.

Anyway, if you don't believe me, then, you are free to refer to the official Cisco website, there you will have the ultimate shock ;-)

-- The hidden trick:

Sometimes, easy things become a nightmare for the engineer whom configuring a router, when configuring a routing protocol, and you think everything is going fine, BUT, the nightmare is: the routing protocol does not work as expected.

Why? Here we begin troubleshooting. And nothing wrong found.

Finally rises the hidden hated trick, the network you are trying to advertise in the routing protocol is one of the subnets assigned to an interface as a secondary IP.

It is that easy, but it turns a journey into a nightmare. Here is the trick: no routing protocol deals with a secondary IP, and even if you add the network statement hundreds of times for that particular subnet, it will not included in the routing protocol calculations.

Just for fun, both of these created problems to me, and turned my funny work into a hell.

I hope it was informative for you,
My regards,

1 comment:

Frreak said...

It will definitely be advertised ... you might have forgotten to disable the split horizon on the interface the secondary address is provided...

Naveen B