3 Replies Latest reply: Mar 19, 2014 11:27 AM by Gary RSS

    DR/ BDR election in ospf

    samsecure09

      Hello Friends ,

       

      I am stuck on one issue.

       

      DR is elected first or BDR .Somehow i came to know BDR is elected first ...please explain/documentation for detailed working for this process

       

      HOW BDR is elected first ??

       

       

       

       

       

      thanks 

        • 1. Re: DR/ BDR election in ospf
          Elvin Arias

          Yeah! I remember the coolest explanation about that from two giants Scott and Petr. I don't going to explain that, because they already did. See the post. https://learningnetwork.cisco.com/thread/33560?start=0&tstart=0

           

          Anyways if you don't understand something, please post.

           

          Elvin

          • 2. Re: DR/ BDR election in ospf
            Brian

            Read RFC 2328 section 9.4 Electing the Designated Router.  This explains the process of electing the BDR and DR.  The BDR is elected first.

             

            Hope this helps.

             

            Brian

             

            • 3. Re: DR/ BDR election in ospf
              Gary

              How OSPF Forms Its Neighbors  In this topology, all routers are running Open Shortest Path First (OSPF) over the Ethernet network:    This is sample output of the show ip ospf neighbor command on R7 and R8:

               

              R7# show ip ospf neighbor   

              Neighbor ID     Pri       State                       Dead Time   Address         Interface  

              170.170.3.4       1       2WAY/DROTHER    00:00:34    170.170.3.4     Ethernet0   

              170.170.3.3       1       2WAY/DROTHER    00:00:34    170.170.3.3     Ethernet0   

              170.170.3.8       1       FULL/DR         00:00:32    170.170.3.8     Ethernet0   

              170.170.3.2       1       FULL/BDR        00:00:39    170.170.3.2     Ethernet0   

               

              R8# show ip ospf neighbor   

              Neighbor ID     Pri       State                      Dead Time   Address         Interface   

              170.170.3.4       1       FULL/DROTHER    00:00:37   170.170.3.4     Ethernet0   

              170.170.3.3       1       FULL/DROTHER    00:00:37    170.170.3.3     Ethernet0   

              170.170.3.7       1       FULL/DROTHER    00:00:38    170.170.3.7     Ethernet0   

              170.170.3.2       1       FULL/BDR        00:00:32    170.170.3.2     Ethernet0

               

               

              13683-11a.jpg

               

              http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13683-11.html

              Can anyone describe to me why R2 is the BDR?

               

              Regards...