Why IP Address gets removed after configuring IP VRF Forwarding

Dear All,

My queries:

Why IP Address gets removed after configuring IP VRF Forwarding on an interface?

Is it an IOS limitation?

Is Cisco doing any enhancement to stop auto removal of ip address from the interface?

 

Merci Beacoup,

Ashish

 

Comments

  • VRF : Virtual Routing and Forwarding means it creates a separate instance of routing table (each VRF uses it's own instance of routing table rather than using the global routing table.) By default all interface belongs to global routing (global VRF). When you enter the ip vrf forwarding command, interface moves from global to that particular VRF but couldn't transfer the IP info (rather than transfering IP info, it removes).

    See here:

    R1(config-if)#do show ip route
    Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route, + - replicated route

    Gateway of last resort is not set

          1.0.0.0/32 is subnetted, 1 subnets
    C        1.1.1.1 is directly connected, Loopback0
          2.0.0.0/32 is subnetted, 1 subnets
    R        2.2.2.2 [120/1] via 192.168.0.2, 00:00:17, FastEthernet1/0
          100.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        100.100.100.0/24 is directly connected, Loopback100
    L        100.100.100.100/32 is directly connected, Loopback100
          192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.0.0/24 is directly connected, FastEthernet1/0
    L        192.168.0.1/32 is directly connected, FastEthernet1/0

    Now Lo100 interface is in global routing table.

    R1(config)#int lo100
    R1(config-if)#ip vrf forwarding TEST
    % Interface Loopback100 IPv4 disabled and address(es) removed due to disabling VRF TEST <-- Because interface is moving from global to TEST VRF
    R1(config-if)#ip add 100.100.100.100 255.255.255.0

    R1#show ip route
    Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route, + - replicated route

    Gateway of last resort is not set

          1.0.0.0/32 is subnetted, 1 subnets
    C        1.1.1.1 is directly connected, Loopback0
          2.0.0.0/32 is subnetted, 1 subnets
    R        2.2.2.2 [120/1] via 192.168.0.2, 00:00:23, FastEthernet1/0
          192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.0.0/24 is directly connected, FastEthernet1/0
    L        192.168.0.1/32 is directly connected, FastEthernet1/0
    R1#sh
    R1#show ip route vrf TEST

    Routing Table: TEST
    Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route, + - replicated route

    Gateway of last resort is not set

          100.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        100.100.100.0/24 is directly connected, Loopback100
    L        100.100.100.100/32 is directly connected, Loopback100

    [:D]

     

  • ashe,

    As nnn wrote, assigning an interface to a VRF places it in a different routing table, which most often will use a different IP address range.

    I don't think there is any reason for Cisco to change this behavior, because it does not make sense to assume that the same IP address will be used in a different VRF.

    The proper order of operations is:

    • Create the VRF with name and RD
    • Assign RT values if using MP-BGP
    • Assign interface to VRF
    • Assign IP address to interface

    In the case where an IP address is assigned to an interface (as in initial configs for Lab Exam), and the interface needs to be placed in a VRF, use "do show running int <type/number>" before applying the "ip vrf forwarding <VRF>" statement.

  • From a programic point of view, i guess it could be done both ways ( with or without removing the ip address configuration). I guess it is only a cosmetic thing, so that the CEF table has more chances to be properly populated with the repsective prefix in the correct VRF.

    Good luck with your studies!

  • i am agree with nnn well this behevour does happens when your interface is the part of global routing table and then you convert this interface to vrf routing table in that case you have to re-assign ip add on this interface for making it to the part of vrf.

    but you can make any interface as the part of vrf routing table without reassigning ip address on the interface :-

    such as:-

    just use interface and provide ip vrf forwording vrf_name after making this interface to the part of vrf then can assign ip addresson this interface. in this process, there would not be any reassigning process

     

    router(config)#interface fast ethernet 0/0

    router(config-if)#ip vrf for VRF_NAME

    router(config-if)#ip address x.x.x.x x.x.x.x

     

    in this process no reassigning process would be happened

  • this is really old post

    but I would like to mention that before when I place ip vrf for instance under interface I am getting at least which IP address was remove - did not say subnet mask but at least you see ip address removed from the interface

    Now as practice on the ver 15.4 - I just see the message from the console that ip address was removed - see bellow

     

    R5(config-subif)#ip vrf for VPN_A
    % Interface GigabitEthernet0/1.58 IPv4 disabled and address(es) removed due to disabling VRF
     VPN_A

     

  • That is the expected result. You deleted the virtual routing table the interface was a member of, therefore the router disables it. Remove the interface from the VRF first, I.E no vrf NAME under the interface and it will be placed in the default VRF which is the global routing table. 

    The same thing happens in a switch, if you place a port in a vlan and then delete the vlan you have essentially deleted the MAC address table and STP instance it was sitting. The port is no longer able to function as it isn't inside of a broadcast domain anymore. You'll notice an amber light on the port. This is classic in VTP environments when the VTP databases get overwritten and the vlan that the port was in is deleted. Just go to the port and tel it switchport access vlan X, where X is an active vlan. 

    HTH
    Rob


    On Monday, January 19, 2015 3:30 PM, amkolev <[email protected]> wrote:


    this is really old post

    but I would like to mention that before when I place ip vrf for instance under interface I am getting at least which IP address was remove - did not say subnet mask but at least you see ip address removed from the interface

    Now as practice on the ver 15.4 - I just see the message from the console that ip address was removed - see bellow

     

    R5(config-subif)#ip vrf for VPN_A
    % Interface GigabitEthernet0/1.58 IPv4 disabled and address(es) removed due to disabling VRF
     VPN_A

     



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