In a previous lesson, I showed you how to configure the OSPF point-to-multipoint network type. This time we’ll look at the OSPF point-to-multipoint non-broadcast network type. It’s the same thing, but we’ll have to specify OSPF neighbors ourselves. Here is the topology that we’ll use:
There are a couple of things that you need to be aware of:
- No Automatic neighbor discovery, so you 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.
Here’s the configuration for the Hub router:
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 non-broadcast Hub(config-if)#exit Hub(config)#router ospf 1 Hub(config-router)#network 192.168.123.0 0.0.0.255 area 0 Hub(config-router)#neighbor 192.168.123.2 Hub(config-router)#neighbor 192.168.123.3
This is the hub configuration. I changed the network type to point-to-multipoint non-broadcast, advertised the 192.168.123.0 /24 network in OSPF, and, most important…specified the OSPF neighbors myself. Let’s look at the spoke router configuration:
When we need Point to multipoint and Point to multi point non- boradcast
This will depend on the underlying Frame-Relay network. When broadcasting is disabled you will have to use the “non-broadcast” network types.
i just dont understand why broadcasting would be disabled? isnt it just a pseudo broadcast for discovering neighbors? I mean does it congest the network or something?
Broadcasting is a very inefficient method for communication. Imagine you had 200 routers and only 10 of them would talk OSPF. When you send a broadcast it means everyone receives it…whether you want it or not. It’s a waste of bandwidth and resources…
I thought we could disable/enable broadcast - on a frameRelay multipoint interface - per PVC by using the Frame-Relay map ip “IP address” “PVC No.” [broadcast] command. So, If I have 200 routers only 10 speak OSPF why Wouldn’t I disable broadcast on the 190 PVCs and enable it on only 190 routers? The only downside of this is having to entre so many lines of mapping. My point is it is technically possible.