Changing MPLS "O IA" to "O" routes

Topology:

R1(CE)/OSPF 1----R3(PE)/OSPF 3----R2(P)----R4(PE)/OSPF 4----R5(CE)/OSPF 1

Initial Output:


R1(config)#do sh ip route | b Gate

Gateway of last resort is not set

 

C    1.0.0.0/8 is directly connected, Loopback0

O E2 5.0.0.0/8 [110/65] via 10.1.13.3, 00:00:13, Serial0/0

     10.0.0.0/24 is subnetted, 2 subnets

C       10.1.13.0 is directly connected, Serial0/0

O E2    10.1.45.0 [110/1] via 10.1.13.3, 00:00:36, Serial0/0

Changes done:


R3(config)#router osp 3 vrf VPNA

R3(config-router)#domain-i 0.0.0.1


R4(config)#router osp 4 vrf VPNA

R4(config-router)#domain-i 0.0.0.1

Changed Output:


R1(config)#do sh ip route | b Gate

Gateway of last resort is not set

 

C    1.0.0.0/8 is directly connected, Loopback0

O IA 5.0.0.0/8 [110/129] via 10.1.13.3, 00:00:17, Serial0/0

     10.0.0.0/24 is subnetted, 2 subnets

C       10.1.13.0 is directly connected, Serial0/0

O IA    10.1.45.0 [110/65] via 10.1.13.3, 00:00:17, Serial0/0

 


My Query:

Since both R1 and R5 are in the same Area 0, can these routes be further changed to O (Intra-Area)

 

Comments

  • In my understanding no because:

    - At the remote PE site, MP-BGP converts the OSPF routes
    to BGP VPN-IPv4 routes and sends them across the BGP/MPLS VPN backbone.

    - At the destination PE, MP-BGP must redistribute the BGP VPN-IPv4 routes
    back into OSPF.

    The PE router becomes the originator of
    the OSPF routes, which are either type 5 external routes or type 3 internal
    routes.

     OSPF Router with ID (192.168.0.2) (Process ID 100)

                    Router Link States (Area 0)

    Link ID         ADV Router      Age         Seq#       Checksum Link count
    1.1.1.1         1.1.1.1         121         0x8000000A 0x00EC52 3
    192.168.0.2     192.168.0.2     119         0x80000004 0x005599 2

                    Summary Net Link States (Area 0)

    Link ID         ADV Router      Age         Seq#       Checksum
    5.5.5.5         192.168.0.2     102         0x80000001 0x008F6C
    192.168.3.0     192.168.0.2     121         0x80000003 0x001DC4

                    Type-5 AS External Link States

    Link ID         ADV Router      Age         Seq#       Checksum Tag
    55.55.55.55     192.168.0.2     104         0x80000001 0x007326 3489660929

    [:D]

  • They can be converted to regular intra-area routes if you use a sham-link. Then the routes will be sourced via OSPF and not iBGP since OSPF has the admin distance 110 and iBGP has 200. You use the sham-link in the same way as a virtual-link. Setup the sham-link between the router-id's. Remember that the shamlink should be sourced from a /32 interface.

  • They can be converted to regular intra-area routes if you use a sham-link. Then the routes will be sourced via OSPF and not iBGP since OSPF has the admin distance 110 and iBGP has 200. You use the sham-link in the same way as a virtual-link. Setup the sham-link between the router-id's. Remember that the shamlink should be sourced from a /32 interface.

    Using a sham-link is the correct tool for the problem, however I don't completely agree with how you describe in configuring one

    On the PE routers (this is all transparent to the CEs):

    1) Create loopbacks within the customer VRF (these will be the /32 interfaces that the sham-link is configured between)

    2) Advertise these networks into the ipv4 unicast address family of the vrf within BGP and filter from being advertised into OSPF

    3) Within the OSPF process for the area then create the sham-link - this will be between the loopbacks defined in step 1 (possibly these will become the router-ids for the OSPF process within VRF if the processes are reloaded but that is not a certainty)

    http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ospfshmk.html#wp1025241

  • Yes,

    You are correct. As we both define source and destination it does not have to be router-id as with the virtual link. It should be advertised into BGP just as you say and best practice is to filter it out from being redistributed into OSPF.

  • AdamBoot,

    Just for solution we can do sham-link. I completely agree with your answer.

    [:D]

  • You still remember those "TUNNEL INTERFACES/GRE TUNNELS" ? [;)]

     

    They can easily help you to fix this too. Though not a scalable design though.

     

    HTH...

    Deepak Arora

    http://deepakarora1984.blogspot.com

  • Do remember to increase the interface ospf cost that is between the CEs so that the intra area routes are more preferred from the sham-link:>

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