8 Replies Latest reply: Apr 13, 2012 8:52 PM by Mr. Akshay J RSS

    OSPF and EIGRP over NBMA

    Mr. Akshay J

      I am going through the CCNP route series.

      NMBA means no broadcast and no multicast.

      So, OSPF and EIGRP uses psedo-broadcast to do their job.



      My first question is, when we put the broadcast keyword in frame relay config, does it mean that the router running OSPF/EIGRP will themselves create pseudo-broadcast or does it mean that the routers will generate ordinary broadcast/multicast packets and its the job of the frame relay clound to convert it into pseudo broadcast.


      Secondly, by using the frame map statements with broadcast keyword, OSPF and EIGRP are able to get their job done over NBMA.

      But in case of EIGRP configuration,I dont have to add any neighbour statements but its needed in the case of OSPF.

      With EIGRP I just need to put the network statements and disable the split horizon(if using multipoint config) and they are good to go, but its not the case with OSPF.

      Why is it so?

        • 1. Re: OSPF and EIGRP over NBMA

          Question #1 - when you add the "broadcast" keyword to your frame-relay map command, it allows the specified DLCI to forward broadcast and multicast packets.  This of course only applies to static frame-relay mappings.  The "frame-relay map" command applies to physical and multipoint subinterfaces only.

          Dynamic mappings (frame-relay inverse ARP enable) allows IP "broadcasts" to got out the interface by default.  You can verify this with the "sh frame-relay map" command and look for the "broadcast" word in the output.  See example below.


          R1#show frame-relay map
          Serial0/0 (up): ip dlci 102 (0x64,0x1840), dynamic,
          broadcast,, status defined, active


          Question #2 - This is because OSPF has many different "network" types when used with frame-relay.  By default, physical and multipoint subinterfaces are non-broadcast with OSPF and require the "neighbor" command under the OSPF process.  To get around this you can change the "default" OSPF network type by using the "ip ospf network" command.


          In the case of dynamic frame-relay mappings you just need to use the "ip ospf network broadcast" command under the physical interface.  If you are using dynamic frame-relay mappings with multipoint subinterfaces then you need the "frame-relay interface-dlci" command and your choice of one of the "ip ospf network" commands.  I say this because depending on if you want a DR/BDR election or not, you will use a different keyword with the command.  Such as the following:



          ip ospf network non-broadcast   <-- requires the "neighbor" command




          ip ospf network broadcast




          No DR/BDR

          ip ospf network point-to-multipoint non-broadcast   <-- requires the "neighbor" command




          ip ospf network point-to-multipoint


          If you are using static frame-relay mappings with multipoint subinterfaces then you use the "frame-relay map" command with "broadcast" keyword.  Again, depending on whether you want a DR/BDR election, you will need to choose one of the "ip ospf network" commands.


          Hope this helps.



          • 2. Re: OSPF and EIGRP over NBMA

            Hi Akshay,


            I think the broadcast keyword has not lost it's meaning as far as EIGRP is concerned. Depending on packet type, EIGRP will use both unicast and multicasts by default for their transmission.


            So its logical if you leave out the "broadcast keyword" on  your map statements you will definately be prohibiting the L2  transmission of the  multicast subset of packets  EIGRP uses accross teh frame.


            In the case you actually leave out the broadcast keyword,  you can then tell EIGRP to rely _ exclusively_  on unicast transmission by using the passive command and neighbor statements in order for adjacencies to form between neighbors.


            I must admit, I haven't tested this on a lab.  Maybe Akshay you can test this bit of theory if its true or not? .   Looks like a fun thing to do when i get time --> force EIGRP to use unicast only he he



            • 3. Re: OSPF and EIGRP over NBMA
              Mr. Akshay J


              All the people explain the theory of it.

              I just found an awesome tutorial here:





              He even configures it.


              Thanks chemilo and Brian !

              • 4. Re: OSPF and EIGRP over NBMA
                Marko Milivojevic

                #1 FrameRelay cloud cannot perform broadcast/multicast replication. When you use "broadcast" keyword, you instruct the router to generate a pseudobroadcast, i.e. perform broadcast/multicast replication itself.


                #2 OSPF reckognizes different network types. Multipoint FrameRelay interfaces are by default "non-broadcast" and as such will only send unicast hellos. Unicast hellos cannot be sent unless you manually specify neighbors. Since IEGRP doesn't have the concept of a non-broadcast interface, this is a non-issue with EIGRP. Technically, for OSPF the problem can be eliminated by changing the interface to either "broadcast" (ip ospf network broadcast) or "point-to-multipoint" (ip ospt network point-to-multipoint).



                Marko Milivojevic - CCIE #18427 (SP R&S)

                Senior CCIE Instructor - IPexpert

                • 5. Re: OSPF and EIGRP over NBMA
                  Mr. Akshay J

                  Hey thanks Marko !

                  • 6. Re: OSPF and EIGRP over NBMA
                    Marko Milivojevic

                    Any time :-)



                    Marko Milivojevic - CCIE #18427 (SP R&S)

                    Senior CCIE Instructor - IPexpert

                    • 7. Re: OSPF and EIGRP over NBMA

                      Hi Akshay,


                      Great feedback from Marko Milivojevic.


                      I agree, a lot of theory. So i've found a lab that focuses on EIGRP on NBMA.






                      I am definately going to lab it up.





                      • 8. Re: OSPF and EIGRP over NBMA
                        Mr. Akshay J

                        Hi Chemillio !

                        Thanks for the Lab.

                        But really EIGRP over NBMA is not that much difficult.


                        You just need to enter the frame relay commands using broadcast keyword, enter the network statements and it works !

                        With OSPF there are lots of network types, making it sometimes confusing.


                        Where do you find such labs ?

                        DO you have some labs for OSPF ?