Assigning an Interface to a VRF

You must assign an interface or subinterface to a VRF so that when the router receives a packet at this interface, it routes the packet using the VRF’s forwarding table rather the global forwarding table. You can assign the interface from outside the context of the VRF or inside the context of the VRF.

To assign an interface to a VRF from outside the VRF context:

1. Select the interface.
2. Specify the VRF to associate with the interface.

   host1:vr1(config)#interface gigabitEthernet 1/0

   host1:vr1(config-if)#ip vrf forwarding vrfA

3. Assign an IP address to the interface because forwarding the interface from the VR to the VRF removes the existing IP configuration from the interface.

   host1:vr1:vrfA(config-if)#ip address 10.16.2.77 255.255.255.0

To assign an interface to a VRF from inside the VRF context:

1. Select the interface.
2. Enter the VRF context.

   host1:vr1(config)#virtual-router :vrfA

3. Associate the interface.

   host1:vr1:vrfA(config)#interface gigabitEthernet 1/0

   In this case, you do not have to reassign an IP address to the interface because you did not use the ip vrf forwarding command.

ip vrf forwarding

• Use to assign a VRF to an interface or subinterface by forwarding the interface from the VR to the VRF. This command also enables you to specify secondary routing table lookup for a VRF, in the event that an initial routing table lookup does not yield results.
• Forwarding the interface removes the IP configuration from the interface. You must reassign an IP address to the interface after you issue this command.
• The ip vrf forwarding command changes the prompt to indicate that the CLI is now in Interface Configuration mode within the child VRF. This condition persists only for as long as you are configuring attributes on the given interface within the VRF. Entering a top-level command, such as interface, within this VRF context takes the CLI out of the VRF context back to the parent VR context.
• When you issue the ip vrf forwarding command from within the Interface Configuration or Subinterface Configuration mode of the parent VR, the IP address and other attributes of the interface are deleted from the interface. You must then reconfigure the IP attributes in the context of the VRF after issuing the command.
• Example

  host1:foo(config-if)#ip vrf forwarding vrfA

  host1:foo:vrfA(config-if)#ip address 10.12.4.5 255.255.255.0

  or

  host1:foo(config-if)#ip vrf forwarding vrfA fallback global

• Use the no version to remove the interface assignment or discontinue secondary routing table lookup.
• See ip vrf forwarding.

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