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:

ospf p2p topology

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 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…

  3. Rene – in my class I have to discuss OSPF over Frame Relay. Im having a hard time grasping this. Specifically - I have to discuss a single subnet for every PVC – or – a single subnet for all routers using point to point subinterfaces associated with each PVC. So my understanding is….

    “Single subnet for all routers” – uses Point to Multi-Point (point to point subinterfaces) –. It’s the Point to Mulit-Point Broadcast and Point to Multi-Point NON Broadcast that is throwing me. I understand Frame Relay is a NonBroadcast MultiAccess (NBMA)…. So what is Point to

    ... Continue reading in our forum

  4. Hi Jason,

    When configuring frame-relay, we have two options:

    The links above will show you a configuration example for each. The main difference is that point-to-multipoint uses a single subnet for all PVCs while point-to-point uses a different subnet for each PVC.

    Now when it comes to OSPF, this can be confusing yes…here are all network types:

    One of the main differences between broadcast/non-broadcast and the point-to-mult

    ... Continue reading in our forum

  5. Hello Michael.

    I refer to yout @ReneMolenaar’s previous post where he states that [quote=“ReneMolenaar, post:24, topic:921”]
    They all work so it doesn’t matter too much which [network topology] you pick.

    The point-to-point or point-to-multipoint network types are probably the easiest to use. You don’t require a DR/BDR election so you don’t have to worry about setting the correct priority.
    [/quote]

    So it really doesn’t matter which network type you choose, as long as they are configured correctly.

    However, keep the following issues in mind:

    * If each area is com

    ... Continue reading in our forum

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