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

Lessons Discussion
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This topic is to discuss the following lesson:

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Keep in mind that the physical interface for frame-relay is always non-broadcast.

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Hi Rene!
I´ve tried the way you said but it didn´t work! So i google it and found a command
Spoke(config-if)# ip ospf network broadcast, after that it worked!

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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…

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Hi Rene!
correct ur code plz!
it needs:

Spoke(config-if)# ip ospf network point-to-point
and without this,

#show ip ospf neighbor
doesnt show anything.
for example I used it in my code and just after that:

Router(config-if)#
00:26:29: %OSPF-5-ADJCHG: Process 100, Nbr 192.168.2.1 on Serial2/0 from LOADING to FULL, Loading Done
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Hi Sarah,

Take a close look at the syslog message of your OSPF neighbor, you are running OSPF on the physical interface. By default OSPF configures the physical interface as “non-broadcast”. If you use a point-to-point sub-interface, OSPF will automatically configure it as the point-to-point network type :slight_smile:

Rene

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ok thanks Rene, I didn’t know this.

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Hey Rene! Congrats on your splendid easy-to-remember OSPF network types. My question is this: why would you wanna use any of these network types? Are there preferable ones over others? Are there any tech limitations between SP’s?

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Hi Apostolis,

Nowadays you really don’t have too worry much about these network types on a real network. For a point-to-point link you can just use “point-to-point” and for Ethernet just use the “broadcast” type. The others are more for networks like frame-relay but you won’t see that much anymore…

Rene

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Just get CCNA today !
Thanks René

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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?

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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

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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

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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

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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 ??

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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

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17

Thanks Rene I got it now

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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

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21

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?

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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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