OSPF peerings over PPPoE link

Just testing ospf peerings over PPPoE links with both peers on different networks. The neighbor peerings do not form and the debug complains about them not being on the same prefix.

*Nov 22 13:40:23.219: IP-EIGRP(Default-IP-Routing-Table:10): Neighbor not on common subnet for Virtual-Access2.1

In RIP we can use the "no validate-update-source" to ignore this issue, is there anything we can do simular in OSPF?



  • I think this only works if you have ip unnumbered.  Did you use unnumbered or hard coded them as different networks?  Also try the point to point network type if you have not done so already.



  • Hi Nick

    I hard coded the servers virtual interface and the client was configured to negotiate. The server was allocating the client from a local pool.

    Tried the p2p and it didnt make any difference.

    Its good to know that OSPF doesnt have any way of allowing this and really why would you do this right, but you just never know when it comes to the lab.



  • Hi Ben


    It will work if you use unnumbered from loopbacks so each router has a completely different network say on R4 and on R5.  With unnumbered and point-to-point the adjaceny will come up and the LSAs will exchange so that would be your option for discontiguous networks and OSPF.



  • OSPF uses the interface index to get around the break between the interface and IP addressing:


    Rack1R4(config-router)#interface-id snmp-if-index 


    Rack1R4#conf t                    

    .Nov 22 17:43:40.772: %SYS-5-CONFIG_I: Configured from console by console

    Rack1R4#sh ip ospf data router se 


                OSPF Router with ID ( (Process ID 1)


    Router Link States (Area 0)


      LS age: 5

      Options: (No TOS-capability, DC)

      LS Type: Router Links

      Link State ID:

      Advertising Router:

      LS Seq Number: 80000004

      Checksum: 0xB3C4

      Length: 48

      Number of Links: 2


        Link connected to: a Stub Network

         (Link ID) Network/subnet number:

         (Link Data) Network Mask:

          Number of TOS metrics: 0

           TOS 0 Metrics: 1


        Link connected to: another Router (point-to-point)

         (Link ID) Neighboring Router ID:

         (Link Data) Router Interface address:

          Number of TOS metrics: 0

           TOS 0 Metrics: 64



    Rack1R4#sh snmp mib ifmib ifindex 

    Virtual-Access2: Ifindex = 12

    FastEthernet0/1.58: Ifindex = 19

    Virtual-Access4: Ifindex = 15

    FastEthernet0/1: Ifindex = 2

    Serial0/1/0: Ifindex = 3

    Async0/2/0: Ifindex = 8

    VoIP-Null0: Ifindex = 5

    FastEthernet0/1.146: Ifindex = 18

    Loopback101: Ifindex = 21

    Loopback0: Ifindex = 9

    Null0: Ifindex = 6

    Serial0/2/0: Ifindex = 4

    Virtual-Access1: Ifindex = 10

    Virtual-Access3: Ifindex = 14

    Async0/1/0: Ifindex = 7

    Tunnel46: Ifindex = 17

    Virtual-Access5: Ifindex = 16

    Virtual-Template1: Ifindex = 11

    Dialer0: Ifindex = 13

    FastEthernet0/0: Ifindex = 1

    Loopback100: Ifindex = 20

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