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I am trying to understand this behavior.

I have an EIGRP router that receives eigrp external route (redistributed from BGP). Lets says 192.168.100.0/24. This route gets advertised further to other eigrp neighbors. However, if I add a static route entry for the same destination, there is no more an advertisement to its neighbors via eigrp.

One possible explanation is that EIGRP behaves as a distant vector as well. is this the distance vector behavior i.e., it builds the routing table and than forwards the advertisement based on the route in the routing table? I thought only RIP did that.

Thanks in advance.

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EIGRP is a distance vector routing protocol. It has some advanced features but at the end of the day it's still distance vector.

While you may have multiple routes in the RIB only the best one gets advertised to your neighbors. EIGRP only advertises routes that are in the RIB as EIGRP.

When you add the static route, it has better AD than the EIGRP route so EIGRP stops advertising the route. You could of course redistribute the static into EIGRP if you want to.

  • Thanks, one more thing I observed was that it will not advertise it only if the static route is an exact entry. If the static entry is less specific, 192.168.0.0/16 in this example, than the EIGRP route will be advertise. I guess this is also because the RIB has EIGRP entry. Will this be the same if static entry is more specific. – Hardy Apr 3 '14 at 21:34
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    It has to be a match to directly compete from a control plane perspective. From a data plane perspective if a packet comes in, the router will look for the longest match regardless of AD of the routes. If you have multiple routes of the same length than AD will decide which one to use. – Daniel Dib Apr 4 '14 at 4:23

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