[j-nsp] PE-CE issue with OSPF routes not getting into routing table

[Raymond, Adam]

Hi,

        Complex one, so I will try to describe this carefully.

        I have a IPv4 layer 3 MP-BGP VPN. There are two PEs that have an OSPF adjacency to CEs inside the VPN. The VPN only has a single OSPF area: 0.0.0.0. An external route, 172.16.64.0/20, is inserted into the VPN (called IP_ASC_VPN_1) via redistribution from iBGP and into OPSF.
        The slightly odd thing about this setup compared to a traditional VPN is that the PEs have devices connected to them that don't support dynamic routing - they are just node with a IP address and default gateway configured on them:

  PE3 -- CE5
  |
  P --------------------------------------------------------------P
  |                                                               |
  P -- PE1 --OSPF-- CE1 --OSPF-- CE2 --OPSF-- CE3 --OSPF-- PE2 -- P
        |                                                   |
       Node                                                Node

All of this works when all of the network is up and operational, but when the link from the P routers to the PEs breaks:
  PE3 -- CE5
  |
  P --------------------------------------------------------------P
  |                                                               |
  P -X- PE1 --OSPF-- CE1 --OSPF-- CE2 --OPSF-- CE3 --OSPF-- PE2 -- P
         |                                                   |
        Node                                                Node

Then the Node closest to the break becomes unreachable from CE5. CE5 is also the router that inserts 172.16.64.0/20 into the VPN. I can log into PE1 by jumping from CE1 and see what is happening on that router. PE1 is still learning the 172.16.64.0/20 route via OSPF as you can see it in the OSFP database:
araymond at PE1> show ospf database external extensive lsa-id 172.16.64.0 instance IP_ASC_VPN_1
    OSPF AS SCOPE link state database
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Extern   172.16.64.0      172.16.49.68     0x80000001   192  0xa2 0xf2f1  36
  mask 255.255.240.0
  Topology default (ID 0)
    Type: 2, Metric: 3000, Fwd addr: 0.0.0.0, Tag: 208.0.255.152
  Aging timer 00:56:47
  Installed 00:03:06 ago, expires in 00:56:48
  Last changed 00:03:06 ago, Change count: 1

where 172.16.49.68 is the router-id of PE2.

The problem is that this route doesn't get added to the IP_ASC_VPN_1.inet.0 routing table. There seems to be something that makes this route ineligible, but I cannot figure out what it is. Can anyone help me with that?

Regards,

Adam Raymond | IP Platform Engineering Team Lead

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