Core Issue
Enhanced Interior Gateway Routing Protocol (EIGRP) uses multicast hello packets to communicate to other EIGRP neighbors.
The issue occurs when EIGRP receives an EIGRP hello packet from an IP address not configured on its receiving interface, as shown in this example:
<timestamp>:IP-EIGRP: Neighbor<neighbor IP address> not on common subnet for <interface>
Resolution
To resolve this issue, verify that the routers on the same segment are configured on the same subnet.
Note: Although not recommended, you can disable messages by issuing the no eigrp log-neighbor-warnings command.
For more information, refer to What Do EIGRP "Not On Common Subnet" Messages Mean?.
