3 Replies Latest reply: May 22, 2019 1:48 AM by Samer RSS

    ospf-transit network

    kp

      Hi,

      Screen Shot 2019-05-21 at 10.14.14 PM.png

       

       

      Can I consider the  192.168.12.0  is transit network

       

       

       

       

      R1

       

      router ospf 1

      network 192.168.13.0 0.0.0.255 area 0

      network 192.168.51.0 0.0.0.255 area 0

      !

       

      r1#sh ip ospf  neighbor

       

      Neighbor ID     Pri   State           Dead Time   Address         Interface

      192.168.51.1      1   FULL/DR         00:00:32    192.168.51.1    GigabitEthernet0/1

      192.168.43.2      1   FULL/DR         00:00:37    192.168.13.2    GigabitEthernet0/0


      And why here showing two DR'S


       

       

       

      R2#sh run | se ospf

      router ospf 1

      network 192.168.23.0 0.0.0.255 area 100

      R2#sh ip ospf  neighbor

       

      Neighbor ID     Pri   State           Dead Time   Address         Interface

      192.168.43.2      1   FULL/DR         00:00:33    192.168.23.2    GigabitEthernet0/0

       

       

       

       

       

      R3#sh run | se ospf

      router ospf 1

      network 192.168.13.0 0.0.0.255 area 0

      network 192.168.23.0 0.0.0.255 area 100

      network 192.168.43.0 0.0.0.255 area 200

      R3#

      R3#sh ip ospf neighbor

       

      Neighbor ID     Pri   State           Dead Time   Address         Interface

      192.168.13.1      1   FULL/BDR        00:00:39    192.168.13.1    GigabitEthernet0/0

      192.168.23.1      1   FULL/BDR        00:00:30    192.168.23.1    GigabitEthernet0/1

      192.168.43.1      1   FULL/BDR        00:00:30    192.168.43.1    GigabitEthernet0/2


      And why here showing multiple BDR'S


       

       

       

      R4#sh run | se ospf

      router ospf 1

      network 192.168.43.0 0.0.0.255 area 200

      R4#sh ip ospf neighbor

       

      Neighbor ID     Pri   State           Dead Time   Address         Interface

      192.168.43.2      1   FULL/DR         00:00:35    192.168.43.2    GigabitEthernet0/0

       

       

       

      R5#sh run | se ospf

      router ospf 1

      network 192.168.51.0 0.0.0.255 area 0

      R5#sh ip ospf neighbor

       

      Neighbor ID     Pri   State           Dead Time   Address         Interface

      192.168.13.1      1   FULL/BDR        00:00:35    192.168.51.2    GigabitEthernet0/0

      R5#

       

       

      Thanks

         
        • 1. Re: ospf-transit network
          Ing_Percy

          Hi!

           

          Your imagen doesn't match to the addresses between R1 and R3 (192.168.13.1 and 192.168.13.2 respectively)

           

          The neighborship between the routers is the following:

          ospf-neigh1.JPG

          According to your outputs:

          router-id of R1 is  192.168.13.1

          router-id of R2 is  192.168.23.1

          router-id of R3 is  192.168.43.2

          router-id of R4 is  192.168.43.1

          router-id of R5 is  192.168.51.1

          kp escribió:

          r1#sh ip ospf  neighbor

          Neighbor ID     Pri   State           Dead Time   Address         Interface

          192.168.51.1      1   FULL/DR         00:00:32    192.168.51.1    GigabitEthernet0/1

          192.168.43.2      1   FULL/DR         00:00:37    192.168.13.2    GigabitEthernet0/0


          And why here showing two DR'S

          It is because R1 sees two neighbors (R3 and R5) and in the DR/BDR election of each segment (R1-R5 and R1-R3) the result was both R3 and R5 became DR routers

           

          kp escribió:

          R3#sh ip ospf neighbor

           

          Neighbor ID     Pri   State           Dead Time   Address         Interface

          192.168.13.1      1   FULL/BDR        00:00:39    192.168.13.1    GigabitEthernet0/0

          192.168.23.1      1   FULL/BDR        00:00:30    192.168.23.1    GigabitEthernet0/1

          192.168.43.1      1   FULL/BDR        00:00:30    192.168.43.1    GigabitEthernet0/2

          And why here showing multiple BDR'S

          It is because R3 sees three neighbors (R1, R2 and R4) and in the DR/BDR election of each segment (R3-R1, R3-R2 and R3-R4) the result was both R1, R2 and R3 became BDR routers


          NOTE: In case of R1, the router-id is 192.168.13.1, but the higher ip address is 192.168.51.2, if you have aggregated this last ip address recently, the router-id won't change. If your want to update it, then you must apply in R1 the command:

          Router#clear ip ospf process


          Best regards!

          • 2. Re: ospf-transit network
            Martin

            Because of default OSPF network type on every Ethernet interface is Broadcast, OSPF elects DR/BDR for each such interface. i.e. R3 has 3 Ethernet interfaces = 3 DR elections

            So, if u have point-to-point links like in your topology (no switches between routers),  you could change type Broadcast to Ospf network type p2p and avoid elections.

            • 3. Re: ospf-transit network
              Samer

              kp wrote:

               

              Hi,

               

               

              Can I consider the  192.168.12.0  is transit network

               

              Yes, and you can see this #show ip ospf database router

               

              kp wrote:

               

              Hi,


              And why here showing two DR'S


               

              R3#sh ip ospf neighbor

               

              Neighbor ID     Pri   State           Dead Time   Address         Interface

              192.168.13.1      1   FULL/BDR        00:00:39    192.168.13.1    GigabitEthernet0/0

              192.168.23.1      1   FULL/BDR        00:00:30    192.168.23.1    GigabitEthernet0/1

              192.168.43.1      1   FULL/BDR        00:00:30    192.168.43.1    GigabitEthernet0/2


              And why here showing multiple BDR'S

               

              On each link there will be election for DR/BDR, unless you change the OSPF network type to Point to point or point to multi-point.