Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

Routing & subnet in EIGRP

Hi All,

I have many routers (> 30) that currently uses EIGRP for routing. I am using segment (example only) , and subnets exists everywhere. Topology is hub-spoke.

So, in my router, the eigrp config look like below:

router eigrp 100

network -----> for LAN segment

network ---> for serial/WAN segment

no auto-summary

eigrp log-neighbor-changes


Site-A & Router A carry -

Site-B & Router B use

Site-C & Router C use, HUB ROUTER with serial links to RouterA, B, D, E and many more....

Site-D & Router D use

Site-E & Router E use


If my WAN link from RouterC to RouterB is down, the eigrp routing table will be updated and all other routers in the network should be are aware of this.

If I perform 'sh ip route' in RouterC, will I get "% Subnet not in table" or will it point to RouterA (since RouterA has/uses) lowest IP subnets?

The reason is , currently in RouterC, when the link to RouterB is down, I am seeing route to is available via RouterA instead of getting "subnet not in table".

Since routing table is already updated and route to is not longer available/reachable (deleted), what is the correct "sh ip route" results?

Is there such thing that eigrp will point the route (to to RouterA since this router carry/has lower subnets?

TQ in adv.



Re: Routing & subnet in EIGRP

The correct result should be "subnet unavailable" or just show the "" that falls into the class A of subnet.

I suspect the problem may be somehere use static route to point to router A as next-hop of router B. Or there is backdoor to learn this route.

Could you post the router A, B & C EIGRP config. for reference ?

Can you issue the clear ip eigrp and check the routing table again ?

Hope this helps.

Re: Routing & subnet in EIGRP

I've tested the 'sh ip route x.x.x.x' where x.x.x.x is unused subnet under The result is "% Subnet not in table".

FYI, we do not use static route, all pure via eigrp. Router config is straight forward

As for now, I can't clear the eigrp route to avoid any disruption to the production network. But I do plan to do so after office hour, but only for subnet

But, is there any (strange) possibility that RouterC will always point to RouterA due to lower IP subnet being used there? It sounds impossible.




Re: Routing & subnet in EIGRP

If there is one subnet w/ shorter mask that include the subnet then the traffic will flow to this route. But the routing table will not show the route. Therefore, it should not display the router A as next-hop. As you said, it is a specific route w/ 24 mask, it is not normal. And I believe there may be some issue in router A to advertise this route.

Can you provide the router A config ?

Or it may be an IOS bug.....

Hope this helps.

Hall of Fame Super Bronze

Re: Routing & subnet in EIGRP


You mentioned you have a hub & spoke configuration and then you mentioned about WAN links from remote site to another remote site in addition to the hub site - I believe this would be a mesh configuration.

On a mesh configuration, what you are seeing is correct. If the WAN Link between B and C goes down, there is still a connection between A and B and that's the reason you are seeing that network via A as a transit network.

EIGRP will announce its connected network as well as any networks participating in the same AS process.



Re: Routing & subnet in EIGRP

Could you please confirm it is purely hub-and-spoke design or mesh design ?

If it is mesh design, please provide the network diagram then we have the clear picture.

Re: Routing & subnet in EIGRP


Given the fact, you mentioned your network is hub-and-spoke and the hub router is routing to subnet via RouterA, when the link to RouterB is down, it's possible that you may have configured a subnet mask on RouterA that includes subnet as well. Obviously, when the more specific subnet becomes unreachable, via RouterB, the less specific route via RouterA becomes the feasible EIGRP route for RouterC to get to network. This is the normal behavior.

If you are still having problems can you post the 'show ip route' from RouterC.



Re: Routing & subnet in EIGRP

Hi All,

Thank you for helping me out. It is a router problem (possibly bugs..) - it advertises subnet that belongs to other router. We'll test it with different IOS ver.




Re: Routing & subnet in EIGRP

Please feel free to let us know the result.