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 exact 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 192.168.123.3This 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:
This will depend on the underlying Frame-Relay network. When broadcasting is disabled you will have to use the “non-broadcast” network types.
Hi Renee
“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.”
Seems to me I have to commit them to memory.
I have to say them out loud day in and day out like a mantra.
I am asking whether or not there is a rhyme or reason to help me memorize or understand them.
In case of PMNB (point to multipoint nonbroadcast) DLCI’s are not configured?
Hi Lee,
I don’t have a rhyme but there’s some logic to these OSPF network types:
Only broadcast and non-broadcast require a DR/BDR election since OSPF sees these network types as “multi-access”. Everything with “point” in it is seen as a collection of point-to-point links so there is no DR/BDR election.
Everything with “non-broadcast” requires you to configure neighbors since OSPF won’t be able to find them by itself.
Only with point-to-point we use a subnet for each PVC, all other OSPF network types usually have a single IP subnet.
Still some memorization to d
... Continue reading in our forumHi, Rene
I hope you are doing great.
I have one question:
- why are you using the command network in order to auto discover the neighbors If you are statically defining them with the command neighbors ?
Have a great day.
Hi John,
Glad to hear you like it. OSPF will change its timers based on its OSPF network type
Rene