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Forum Replies

  1. Hi Rene

    Could you clarify the differences between this and OSPFv3 Prefix Suppression?

    I believe the main difference is that type 8’s and 9’s are suppressed rather than type 1 or 2’s.

    Are stub’s advertised as /128’s?

    Also how does OSPF detect that a prefix is part of a transit network?

  2. Hi @chrisnewnham17,

    In OSPFv3, there is no prefix information in LSA type 1 and 2 anymore, you can find those in LSA type 8 and 9 so yes, OSPFv3 prefix suppression removes it from LSA type 8 and 9.

    About the prefix / transit network. Here’s a quick example with three routers connected like this:

    R1-R2-R3

    All routers are in area 0 and R3 is the DR:

    R3#show ipv6 ospf database prefix self-originate  
    
                OSPFv3 Router with ID (3.3.3.3) (Process ID 1)
    
                    Intra Area Prefix Link States (Area 0)
    
      LS age: 8
      LS Type: Intra-Area-Prefix-LSA
      Link State ID: 0
      Advertising Router: 3.3.3.3
      LS Seq Number: 80000002
      Checksum: 0x7834
      Length: 52
      Referenced LSA Type: 2001
      Referenced Link State ID: 0
      Referenced Advertising Router: 3.3.3.3
      Number of Prefixes: 1
      Prefix Address: 2001:DB8:3333:3333::3
      Prefix Length: 128, Options: LA, Metric: 0
    
      LS age: 1729
      LS Type: Intra-Area-Prefix-LSA
      Link State ID: 3072
      Advertising Router: 3.3.3.3
      LS Seq Number: 80000001
      Checksum: 0x16FD
      Length: 44
      Referenced LSA Type: 2002
      Referenced Link State ID: 3
      Referenced Advertising Router: 3.3.3.3
      Number of Prefixes: 1
      Prefix Address: 2001:23:23:23::
      Prefix Length: 64, Options: None, Metric: 0
    

    Above you can see the referenced LSA type:

    • 2001: Associated with the router
    • 2002: Associated with the Network LSA

    The 2001:23:23:23:: prefix is configured on an Ethernet network, thus it shows up with LSA type 2002. You can also see the link state ID (3) of the advertising router (R3 our DR).

    R3#show ipv6 ospf database network self-originate 
    
                OSPFv3 Router with ID (3.3.3.3) (Process ID 1)
    
                    Net Link States (Area 0)
    
      LS age: 426
      Options: (V6-Bit, E-Bit, R-Bit, DC-Bit)
      LS Type: Network Links
      Link State ID: 3 (Interface ID of Designated Router)
      Advertising Router: 3.3.3.3
      LS Seq Number: 80000002
      Checksum: 0x41A3
      Length: 32
            Attached Router: 3.3.3.3
            Attached Router: 2.2.2.2
    

    About the stub, you mean a stub network? Loopbacks are advertised with a /128, similar to how OSPFv2 advertises them as a /32 by default.

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