Question

A network engineer is provisioning a new MPLS L3VPN customer on a PE router. The PE-CE link uses interface GigabitEthernet0/1 with IP address 10.20.30.1/30 already configured. After creating the VRF and applying it with the command 'ip vrf forwarding CUST_A' under GigabitEthernet0/1, the engineer notices that OSPF adjacency to the CE has dropped and the interface no longer has an IP address in the global table. What is the cause of this behavior?

Accepted Answer

Applying 'ip vrf forwarding' to an interface removes any previously configured IP address, which must be re-entered after associating the VRF.

Answer

The VRF was created without a route distinguisher, so the interface IP address was automatically withdrawn until an RD is configured.

Answer

OSPF cannot run on VRF interfaces, so the IP address was removed to prevent an invalid configuration.

Answer

The interface must be shut down before 'ip vrf forwarding' is applied, otherwise the IOS discards both the IP address and routing state.