Trying to better understand eIGRP .. few questions

[cyr0n_k0r]

So I get the concept of eIGRP and even know how to deploy it in our routers here and it works. My questions is this.

Our network naming is say.. 10.10.x.x
We split that into /21's so each building starts at a multiple of 8. 0, 8, 16, 24, etc.
So each core router would be 0.1, 8.1, 16.1, etc.

eIGRP works, but I'm wondering why when I do a show eigrp neighbors the IP's of the neighbors is returned as 10.10.255.x
There is nothing in the config that specifies a 10.10.255 address. I'm just trying to figure out where those IP's came from. Is it something the router does automatically?

 

[mattjw916]

My first question would be, "Why are you using a little "e"." It's just called EIGRP.

Secondly, if you are doing a "sh ip eigrp neigh" the output of the command shows what your adjacent devices are from a routing perspective. The IP address wouldn't show up in the local config since that command tells you what the other device's addresses are that are exchanging routing information with your local router.

If you really want to know where the address is coming from then crawl through the ARP and CAM tables to find out what port the IP is coming from and examine the device.

 

[xphil3]

eIGRP works, but I'm wondering why when I do a show eigrp neighbors the IP's of the neighbors is returned as 10.10.255.x
There is nothing in the config that specifies a 10.10.255 address. I'm just trying to figure out where those IP's came from. Is it something the router does automatically?

EIGRP cannot just arbitrarily pick a router-id without some kind of interface configuration, so if you're seeing that as a neighbor ID then the neighbor actually has that address configured as the highest loopback/physical interface or you found a bug.

This is basic EIGRP btw, you may need to go over the concepts again.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800949ab.shtml

If you really want to know where the address is coming from then crawl through the ARP and CAM tables to find out what port the IP is coming from and examine the device.

wut? Apparently you need to go over your eigrp concepts again as well.

 

[calvinj]

While your going back over the concepts of EIGRP start thinking about what happens when you integrate a router or switch that isn't cisco. Then your going to have to mess with redistribution between compatible protocols. I used EIGRP in my lab because it was quick and easy, but go back and rethink if EIGRP fits in everything your doing in your network