OSPF - Part 9

OSPF Frame relay

  In previous blogs I explained the OSPF Non-Broadcast network type.

  Let's we are discuss about OSPF frame relay network.

  When ospf is run on a network, two important events occurs before routing information is   
   exchanged.

     1.) OSPF neighbors are discovered using multicast hello packet.
     2.) For a multi-access network (like ethernet and frame-relay), a DR and BDR are elected. All 
           routers on that segment from adjacency with the DR and BDR only.


             Hello packets are multicast to 224.0.0.5 address. In order for the Hello packets to reach 
            remote routers, the underlying Layer 2 technology must allow broadcast/multicast packets 
            to be forwarded. Frame-relay, inherently, does not forward broadcast or multicast packets
           to be sent. Hence, in NBMA network topology, the neighbors are not discovered automatically.
             Neighbors must be configured manually. OSPF elects DR and BDR for every multi-access    
           network. In a frame-relay hub-and-spoke environment, ideally, the Hub router must be made   
            the DR.


The below network is a simple hub-and-spoke topology. Each Spoke router has a single DLCI towards the Hub router. The Hub has multiple DLCIs towards Spoke routers 

    Configure OSPF Frame relay:


    1.) Provide IP address 

             On Hub Router


             Router(config)# interface serial 1/0
             Router(config-if)# ip address 10.1.1.1 255.255.255.0
             Router(config-if)# no shutdown
             Router(config-if)# exit

             Router(config)# interface loopback 1
             Router(config-if)# ip address 1.1.1.1 255.255.255.0
             Router(config-if)#exit



             On Spoke 1 Router
             
             Router(config)# interface serial 1/0
             Router(config-if)# ip address 10.1.1.2 255.255.255.0
             Router(config-if)# no shutdown
             Router(config-if)# exit


             Router(config)# interface loopback 1
             Router(config-if)# ip address 2.2.2.2 255.255.255.0
             Router(config-if)#exit

             On Spoke 2 Router
              
             Router(config)# interface serial 1/0
             Router(config-if)# ip address 10.1.1.3 255.255.255.0
             Router(config-if)# no shutdown
             Router(config-if)# exit


             Router(config)# interface loopback 1
             Router(config-if)# ip address 3.3.3.3 255.255.255.0
             Router(config-if)#exit


Now Configure Frame relay switch

        (Note : Configure Frame relay switch same as EIGRP Frame relay switch To view its   
                      configuration  view EIGRP frame relay blog.)


  
            Now configure Frame relay end point

           On Hub Router
            
            Router(config)# interface serial 1/0
            Router(config-if)# encapsulation frame-relay
            Router(config-if)#exit

             On Spoke 1 Router
            
            Router(config)# interface serial 1/0
            Router(config-if)# encapsulation frame-relay
            Router(config-if)#exit
       
             On Spoke 2 Router
            
            Router(config)# interface serial 1/0
            Router(config-if)# encapsulation frame-relay
            Router(config-if)#exit

            
             Now Configure OSPF 

            On Hub Router 
           
            Router(config)# router ospf 1
            Router(config-if)# network 10.1.1.0 0.0.0.255 area 0
            Router(config-if)# network 1.1.1.0 0.0.0.255 area 0
            Router(config-if)# exit

           On Spoke 1 Router 
           
            Router(config)# router ospf 1
            Router(config-if)# network 10.1.1.0 0.0.0.255 area 0
            Router(config-if)# network 2.2.2.0 0.0.0.255 area 0
            Router(config-if)# exit
     
           On Spoke 2 Router 
           
            Router(config)# router ospf 1
            Router(config-if)# network 10.1.1.0 0.0.0.255 area 0
            Router(config-if)# network 3.3.3.0 0.0.0.255 area 0
            Router(config-if)# exit

Let's If we are check connectivity Between Hub's loopback to Spoke1's loopback, it's fail. Because if 
we are check neighbor using this command show ip ospf neighbor. There is no any one neighbor.

Since Here the router realizes that it is connected to an NBMA network where broadcast and multicast packets are not forwarded, it does attempt to send any hello packets.

Instead, a neighbor command is require under ospf configuration on the Hub router for each spoke 
router.

       Let's configure neighbor manually

        On Hub Router

        Router(config)# router ospf 1
        Router(config-router)# neighbor 10.1.1.2
        Router(config-router)# neighbor 10.1.1.3
        Router(config-router)# exit

        On Spoke1 Router

        Router(config)# router ospf 1
        Router(config-router)# neighbor 10.1.1.1
        Router(config-router)# exit

       On Spoke2 Router

        Router(config)# router ospf 1
        Router(config-router)# neighbor 10.1.1.1
        Router(config-router)# exit


If connectivity problem than use following command on Hub, spoke1 and spoke2 router:

       Router(config)# interface serial 1/0
       Router(config-if)#ip ospf network broadcast
       Router(config-if)# exit   

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