A prerequisite for a neighbor adjacency to form between two directly connected routers is Layer 3 connectivity. By examining the output of the show ip interface brief command, a network administrator can verify that the status and protocol of connecting interfaces are up. A ping from one router to another, directly connected router, should confirm IPv4 connectivity between the devices. The figure displays the show ip interface brief command output for R1. R1 shows connectivity to R2, and pings are successful.
If the ping is unsuccessful, check the cabling and verify that the interfaces on connected devices are on a common subnet. A log message that states that EIGRP neighbors are not on common subnet indicates that there is an incorrect IPv4 address on one of the two EIGRP neighbor interfaces.
EIGRP for IPv6
Similar commands and troubleshooting criteria also apply to EIGRP for IPv6.
The equivalent command used with EIGRP for IPv6 is show ipv6 interface brief.