VMware NSX

In the OSFP protocol, if the FA address in the Type 5 LSA is not 0, then the ASBR itself can go to the external route, and other routers will go to the external network through it.

In NSX, the OSPF-enabled DLR is an ASBR. Because its downlink interfaces do not enable OSPF, these network segments are introduced into OSPF through redistribution.

But on the physical router interconnected with the Edge upstream interface, I see that the FA address in the Type 5 LSA is the same as the DLR forwarding address.

This is what VMware has deliberately set so as to distinguish it from the protocol address, or is it defined by RFC?

If I am not wrong the above topology matches with your query ?

If that said then if the redistribution is being done by DLR then the FA must be 1.1.1.1 ( Which will describe DLR identity )

So from Link state protocol it makes sense, which will go through recursive routing process and when processing traffic for 192.168.1.0/24 it will do recursive routing for ASBR which is 1.1.1.1

This is the output what I got when checked on Cisco RTR:

RTR22#show ip ospf database external

            OSPF Router with ID (10.21.22.22) (Process ID 1)

  Type-5 AS External Link States

  Routing Bit Set on this LSA in topology Base with MTID 0

  LS age: 641

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

  LS Type: AS External Link

  Link State ID: 192.168.1.0 (External Network Number )

  Advertising Router: 20.20.20.20

  LS Seq Number: 80000001

  Checksum: 0xD015

  Length: 36

  Network Mask: /24

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

  MTID: 0

  Metric: 20

  Forward Address: 0.0.0.0 ( I hope this got changed in NSX setup to DLR IP )

  External Route Tag: 0

0.0.0.0 here means to look to advertising router which is recursive routing , but when NSX advertises it makes the recursive lookup simple.

I hope this answer your query.