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New Member

EIGRP over un-numbered interfaces


I am trying to implement EIGRP between Two routers have private point-point T1 over Serial Interfaces. Serial interfaces are configured with "un-numbered ethernet 0".

1. Are there any potentinal problems in this setup ?

2. Should i define IP address on both serial interfaces instead of using "ethernet interface's IP address" ?

3. Current software is 12.0(5), i probably should upgrade ?

\\ Naman


Re: EIGRP over un-numbered interfaces

1. I dont see any problems in using un-numbered. Works fine.

2. If I have IPs available I would use them.

3. I think your IOS is preety up to date.


Re: EIGRP over un-numbered interfaces


I dont think there should be any potential issues, ( though i havent looked at any bugs related to 12.0(5) and unnumbered interfaces with EIGRP as routing protocol)

WHen you use unnumbered interfaces, the routes learned from neighbor, will be installed with the unnumbered interface as the next-hop.

YOu wont be able to ping the interface to see if the interface is up, coz the interface doesnt have an ip address.

You wont be able to use SNMP to monitor the interface.

Hope that helps.

New Member

Re: EIGRP over un-numbered interfaces

Besides what the other posts have said, ip-unnumbered is a classful feature so you loose the VLSM given by using EIGRP. Also you should always use a loopback address for ip-unnnumbered so the route stays in the route table in the event of route "flapping" or the connection is lost. Also EIGRP will use the loopback add insted of the largest interface ip add for determining adjacentcies/neighbors. If you have the addresses to spare for your serial interfaces that would be best( you can use /30 subnet so you only loose 4 host numbers- ex:, .0 and .3 would not be used.

Hope this helps!


Re: EIGRP over un-numbered interfaces

Unless you are trying to do this on a multi-homed, meshed network, there are no problems.

If you are trying this on a meshed network you may see multi-site multicast traffic go up.

I concur that there should not be an issue if you have made use of loopback interfaces.

New Member

Re: EIGRP over un-numbered interfaces

Thanks all. I configured Numbered Serial interfaces and so far everything looks good with EIGRP.

I did have problems before running EIGRP over un-numbered interfaces before with Packets going into a loop between the EIGRP nodes. I was using 10.3.x.x\16, 172.16.x.x.\16 networks as un-numbered interfaces so maybe it was due to the class-full feature of Un-Numbered interfaces ?

Also i did up-grade the software from 12.0 to 12.2, so am not sure what fixed the problem.

\\ Naman

New Member

Re: EIGRP over un-numbered interfaces

An interesting aside

I have found that running ip unnumbered loopback int on GRE tunnels doesn't work with EIGRP. You have to number the interfaces { in this case tunnels}, then a neighbour relationship is formed.