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)#interface serial 0/0.102 point-to-point 
Hub(config-subif)#ip address
Hub(config-subif)#frame-relay interface-dlci 102
Hub(config)#interface serial 0/0.103 point-to-point
Hub(config-subif)#ip address
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
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
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.

    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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