OSPF Point-to-Point Network Type over Frame-Relay

Just get CCNA today !
Thanks René

thanks for this awesome lesson and breakdowns of network types, i understand them clearly.
Just a question, what does multipoint on subinterface do? like “int s1/0.111 multipoint” is it the same with point-to-multipoint?

Hi John,

By default the physical interface for frame-relay is always point-to-multipoint. If you only have point-to-multipoint then there’s no need to use the sub-interface.

If you have a combination of point-to-point and point-to-multipoint then you should create sub-interfaces, one for point-to-point and another for point-to-multipoint.

Rene

Hi Rene,

You mentioned that Point-to-Point Connection also Can be used for single IP subnets ? How can this happen ? I think we have overlabs with sub-interfaces ? or I’m wrong ?
Can you please explain what do you mean at this point ?

hussein sameer

Hi Hussein,

Point-to-point is used when you have one subnet per PVC, unlike point-to-multipoint where you can have one subnet for multiple PVCs.

What do you mean with the overlapping sub-interfaces? we don’t have any here :slight_smile:

Rene

Hi Rene,

At the beginning of lesson you mentioned that we have to know four things about OSPF point-to-point :-

1- Automatic neighbor discovery so no need to configure OSPF neighbors yourself.
2 - No DR/BDR election since OSPF sees the network as a collection of point-to-point links.
3 - Normally uses for point-to-point sub-interfaces with an IP subnet per link.
4 - Can also be used for single IP subnets.

I did not understand the last one ??

Hi Hussein,

I just reworded it as it sounds a bit confusing. What I meant is that you can use OSPF point-to-point as well on frame-relay topologies where you have multiple PVCs and only one subnet.

Rene

Thanks Rene I got it now

Nice article.

But is it possible to simplify examples with ethernet also ?

In a datacenter its hard to find serial interfaces.

Hi Ajith,

The reason we use frame-relay here is because it’s a CCNP ROUTE topic.

On Ethernet interfaces, it’s much simpler…the default OSPF network type is “broadcast” and there’s not really a reason to change it. If it’s an Ethernet link between two routers then you could change it to point-to-point since there’s no reason to have a DR/BDR election there.

Rene

Thanks for the reply Rene.

yeah i agree with you as OSPF topics are designed as CCNP ROUTE topic.

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 Multipoint Broadcast?

“Single subnet for all routers using point to point subinterfaces associated with each PVC” - is this point-to points?

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-multipoint network types is the next hop that we use, take a look here:

OSPF network types IP next hop

Frame-relay is NBMA but with the correct frame-relay maps, we can “emulate” broadcast traffic so that you can forward multicast/broadcast traffic on the PVCs.

Rene

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Hi Rene,

So with those types of network types ( so far 5 ) , is there any preference to use one over the other for frame relay and why ?

thx

Ahmad

Hi Ahmad,

They all work so it doesn’t matter too much which one 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.

Rene

19 posts were merged into an existing topic: OSPF Point-to-Point Network Type over Frame-Relay

I have a customer that is designing 4 areas in a ring configuration using /30s to Area 0 /24 DR and asked if he could make the 4 area rings network point to point connections between each router. Is this a good design? I told them it should be OK as long as a DR/BDR lived in Area 0.

Thoughts

Mike C.

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 composed of a point to point connection between routers, you do not require DR/BDRs at all.
* Secondly if you are creating four areas and these areas connect to each other in a ring topology, then one of these areas will not be directly connected to area 0. You will require either a virtual link (which is not advisable as a permanent solution) or you will need to revise the topology.

I hope this has been helpful!

Laz

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Hi Rene,
Why there is no Point-To-Point non-broadcast type, I mean by the Design of OSPF why there is no such type ??
Kind Regards,
Hussein Samer

Hi Hussein,

There’s no need to, at the other end of a point-to-point connection there is only 1 other device…

Broadcast traffic can be used on multi-access network, like Ethernet where you want everyone to receive certain traffic.

Rene