BGP -> OSPF Down bit

[John Blakley]

It's my understanding that a learned route via BGP by a PE and it's redistributed into OSPF, it will set the down bit. I'm trying to see this happen, but it's not. I have 2 CEs and 2 PEs in gns.

CE1 --> PE1 <----> PE2 ----> CE2

I have a route advertised by CE1 via OSPF to PE1. PE1 sends to PE2 and PE2 sends to CE2. Doing a wireshark capture shows that the down bit isn't set and looking at the LSA for that network isn't set either. Are there special circumstances or configurations to get this to work? My understanding is that it should work by default....

R16#sh ip ospf data exter 25.25.25.25

            OSPF Router with ID (16.16.16.16) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA

  LS age: 26

  Options: (No TOS-capability, DC)

  LS Type: AS External Link

  Link State ID: 25.25.25.25 (External Network Number )

  Advertising Router: 172.1.162.2

  LS Seq Number: 80000003

  Checksum: 0x1C24

  Length: 36

  Network Mask: /32

        Metric Type: 2 (Larger than any link state path)

        TOS: 0

        Metric: 20

        Forward Address: 0.0.0.0

        External Route Tag: 3489662162

Thanks,

John

[Vaibhava Varma · Accepted solution]

Hi John

As per my understanding Down Bit is not supported by a Type 5 External LSA but only Type 3 LSA.

For Type LSA we use Domain-Tag for preventing Loops.

Hope this helps to answer your query.

Regards

Varma

[John Blakley]

Okay...here's what I did, and you pointed me in the correct direction:

I found that if the domain-id's don't match, I was getting everything as type 5 LSAs. I configured the domain id under the ospf process for the CEs to be the same. I then started to get the type 3 LSAs instead of the type 5.

LS age: 63

  Options: (No TOS-capability, DC, Downward)

  LS Type: Summary Links(Network)

  Link State ID: 15.15.15.15 (summary Network Number)

  Advertising Router: 172.1.81.1

  LS Seq Number: 80000001

  Checksum: 0xE450

  Length: 28

  Network Mask: /32

        TOS: 0  Metric: 75

Thanks!

John