OSPF Point-to-Point Network Type over Frame-Relay

In a number of lessons, I covered the OSPF network types. This lesson is the final one and will cover the OSPF Point-to-Point Network Type. I will be using a frame-relay point-to-point topology to demonstrate it, here it is:

Frame Relay P2p Lab Topology Serial

Here’s what you need to know about OSPF point-to-point:

  • Automatic neighbor discovery so no need to configure OSPF neighbors yourself.
  • No DR/BDR election since OSPF sees the network as a collection of point-to-point links.
  • Normally uses for point-to-point sub-interfaces with an IP subnet per link.
  • Can also be used with multiple PVCs using only one subnet.

Let me show you the configuration of the Hub router:

Hub(config)#interface serial 0/0
Hub(config-if)#encapsulation frame-relay 
Hub(config-if)#exit
Hub(config)#interface serial 0/0.102 point-to-point 
Hub(config-subif)#ip address 192.168.12.1 255.255.255.0
Hub(config-subif)#frame-relay interface-dlci 102
Hub(config-subif)#exit
Hub(config)#interface serial 0/0.103 point-to-point
Hub(config-subif)#ip address 192.168.13.1 255.255.255.0
Hub(config-subif)#frame-relay interface-dlci 103

I am using two sub-interfaces and assigning the correct DLCI number to each sub-interface. Now let’s configure the spoke routers:

Spoke1(config)#interface serial 0/0
Spoke1(config-if)#encapsulation frame-relay 
Spoke1(config-if)#interface serial 0/0.201 point-to-point
Spoke1(config-subif)#ip address 192.168.12.2 255.255.255.0
Spoke1(config-if)#frame-relay interface-dlci 201
Spoke2(config)#interface serial 0/0
Spoke2(config-if)#encapsulation frame-relay 
Spoke2(config-if)#interface serial 0/0.301 point-to-point
Spoke2(config-subif)#ip address 192.168.13.3 255.255.255.0
Spoke2(config-if)#frame-relay interface-dlci 301

Above you see a sub-interface for each spoke router with the correct DLCI number.

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Forum Replies

  1. Keep in mind that the physical interface for frame-relay is always non-broadcast.

  2. Hi Rene!
    I´ve tried the way you said but it didn´t work! So i google it and found a command
    Spoke(config-if)# ip ospf network broadcast, after that it worked!

  3. Hi Gabriel,

    OSPF network broadcast will work but it’s normally used for frame-relay point-to-multipoint topologies like in this example. For frame-relay point-to-point it’s best to use the point-to-point or point-to-multipoint network type.

    On the other hand, you can make all the OSPF network types work on any given topology…

  4. Hi Rene!
    correct ur code plz!
    it needs:

    Spoke(config-if)# ip ospf network point-to-point
    and without this,

    #show ip ospf neighbor
    doesnt show anything.
    for example I used it in my code and just after that:

    Router(config-if)#
    00:26:29: %OSPF-5-ADJCHG: Process 100, Nbr 192.168.2.1 on Serial2/0 from LOADING to FULL, Loading Done

  5. Hi Sarah,

    Take a close look at the syslog message of your OSPF neighbor, you are running OSPF on the physical interface. By default OSPF configures the physical interface as “non-broadcast”. If you use a point-to-point sub-interface, OSPF will automatically configure it as the point-to-point network type :slight_smile:

    Rene

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