OSPF Point-to-Multipoint over Frame-Relay

In previous lessons I explained the OSPF non-broadcast and broadcast network types. Now we are going to look at the OSPF point-to-multipoint network type. This is the topology that we will use:

OSPF Network Type Topology

There are a couple of things that you need to be aware of:

  • 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.
  • Only a single IP subnet is used in the topology above.
  • Make sure your frame-relay network is configured with the broadcast keyword.

Let’s take a look at the configuration:

Hub(config)#interface serial 0/0
Hub(config-if)#ip address 192.168.123.1 255.255.255.0
Hub(config-if)#encapsulation frame-relay
Hub(config-if)#ip ospf network point-to-multipoint
Hub(config-if)#exit
Hub(config)#router ospf 1
Hub(config-router)#network 192.168.123.0 0.0.0.255 area 0

This is the hub configuration. I changed the network type to point-to-multipoint and advertised the 192.168.123.0 /24 network in OSPF. Let’s look at the spoke router configuration:

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Forum Replies

  1. Hello Sims!

    The network topology that you are describing would not COMPLETELY simulate the frame relay situation in this lesson. What you are describing would require all communication between R1 and R3 to go through R2 just like in the lesson, however, this also means that the two interfaces on R2 that connect R1 and R3 would have to be on the same subnet, something that is not possible. So you would just be creating two point to point links on different subnets, however, in the frame relay example in the lesson, all three routers are in the same subnet.

    Wha

    ... Continue reading in our forum

  2. Hello Sims!

    Although I’m sure you know most of this, let me start by stating the network types for OSPF and stating an example for each:

    **Point to Point** - a serial connection between two routers
    **Broadcast** - two or more routers on the same subnet connected to an Ethernet switch

    The next two types of network are used to accommodate multi access technologies that don’t support broadcast. These technologies include Frame Relay and ATM.

    **Non Broadcast Multi Access** - This is used when you have multiple routers connected on the same subnet over a non-broadc

    ... Continue reading in our forum

  3. Hello Laz,

    Thank you so much for your guidance, this absolutely cleared my doubt.

    Regards,
    Nanu

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