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Luke Poskitt

EIGRP L3Out Best Practice

Hi All,

My environment: ACI fabric with two spine and two leaf switches, with both leaf switches attached to two EIGRP routers with all leaf switches and routers in the same AS.

After reading through the ACI L3Out EIGRP support and best practice documentation, I understand that multiple EIGRP L3Outs on the same border nodes are not supported, so I believe that I should be configuring a single EIGRP L3Out with each leaf defined in a Logical Node Profile and with the connected interfaces defined as Logical Interface Profiles beneath their respective node - in my environment I am using SVIs as the routers are physically connected via port-channels.

After configuring the fabric in this way, the L3Out is working as expected, however HELLOs from both leaf switches appear to be also sent out the other leaf switches interface - i.e. from leaf 1 -> via the fabric -> out leaf 2's interface.

This isn't really a problem, and I can understand why it is happening, but it is resulting in lots of "neighbor blocked: not on common subnet" messages being logged on the routers (due to the Logical Interface Profile SVIs using /30's).

Is there any way in which to prevent leaf 1 from trying to establish adjacency via leaf 2's interface, or is there a better design that could be used here (e.g. a single SVI on a VPC spanning both leaf switches)?



Cisco Employee



Do you have more than one EIGRP device you are connecting to? If so are they all connecting to the same border leafs? Also, are they in the same or different AS? If you have multiple EIGRP devices in the same AS connected to the same border leaf then one L3Out should be used. We support having mutliple connections to external networks from the same border leaf switches there are just some caveats depending on design. 


Please clarify and I will get back to you.



Michael G.