EIGRP specific route reachability

r-tyrell · ‎06-11-2007

We are bringing up a new non-trunking core. Our current core has a 10.0.0.0/16 network management VLAN. The new core has a 10.0.20.0/24 network management VLAN. With the current setup I am unable to reach the /24 from the /16 VLAN. I believe this is due to the fact that EIGRP sees the /24 belonging to the /16 VLAN. I can reach the /24 from a server if I add a static route on the server itself. I have included an attachment that hopefully explains the setup. It is hard to include all the information so please let me know if you need more info. Thank you!

Edison Ortiz · ‎06-11-2007

This is not an EIGRP problem since the default gateway 10.0.0.1 knows how to get to 10.0.20.0/24

The problem is with the hosts in 10.0.0.0/16 not using the default gateway for 10.0.20.0/24 since ,as you stated, the route is local - so unless you change the subnets, you will have to manually input static routes on each host.

anandramapathy · ‎06-11-2007

How difficult will it be for you to change the subnet mask for the int vlan 910 to a /24 & all machines associated with this ?

Richard Burts · ‎06-11-2007

EIGRP is certainly able to do this. It will track the different prefix lengths and both subnets should be in the routing table. I believe that the issue is that the server is sending an ARP request for the destination address of 10.0.20.x instead of forwarding to the default gateway. I believe that if you were to enable proxy arp that this network would work. As it is the server believes that 10.0.20.x is within the local subnet of 10.0/16 and so it arps for the address directly instead of sending it to the default gateway. If proxy arp were turned on I believe that the gateway would respond to the ARP request and the packet could be forwarded.

HTH

Rick

HTH

Rick

r-tyrell · ‎06-11-2007

You guys rock! I turned on ip proxy-arp for the 910 VLAN and now I can successfully reach the 920. Thanks you!!

-Rick

Richard Burts · ‎06-11-2007

Rick

I am glad that our discussion was able to help you resolve your problem.

HTH

Rick

HTH

Rick

r-tyrell · ‎06-11-2007

Thanks for the reply. So by changing the 910 to /24 that should solve my problem? It would be somewhat painful to change all of our 910 devices to the /24 but if that is what we have to do. I wasn't sure if there were some fancy tricks with EIGRP that could produce a workaround.