Question

A network engineer converts an EIGRP classic configuration to EIGRP named mode on a distribution switch. After the migration, the switch no longer forms an adjacency with a neighbor on GigabitEthernet1/0/1, though the interface is up/up and IP connectivity to the neighbor's interface is confirmed via ping. The relevant configuration is:

router eigrp CORP
  address-family ipv4 unicast autonomous-system 100
    af-interface default
      passive-interface
    exit-af-interface
    af-interface GigabitEthernet1/0/2
      no passive-interface
    exit-af-interface
    network 10.0.0.0
  exit-address-family

What is the most likely cause of the missing adjacency on Gi1/0/1?

Accepted Answer

The 'af-interface default' passive-interface command marks all interfaces passive, and only Gi1/0/2 was explicitly re-enabled, so Gi1/0/1 remains passive and suppresses hellos.

Answer

Named mode requires a separate 'network' statement per interface, and Gi1/0/1 is not covered by the 10.0.0.0 network command.

Answer

The autonomous-system number under the address-family must match the interface bandwidth, causing an AS mismatch on Gi1/0/1.

Answer

Named mode disables split horizon by default, which prevents hellos from being sent out Gi1/0/1.