2 Replies Latest reply on Apr 9, 2019 3:10 AM by abhishekkunal5125

    OSPF LSA TYPE 5 released by the DLR

    Silen Lurker

      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?

        • 1. Re: OSPF LSA TYPE 5 released by the DLR
          abhishekkunal5125 Lurker

           

          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

          • 2. Re: OSPF LSA TYPE 5 released by the DLR
            abhishekkunal5125 Lurker

            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.