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New Member

point-to-multipoint and point-to-multipoint non-broadcast

Internetwork Expert Lab for CCIE says:

"Another two configurable network types that are left

are therefore point-to-multipoint and point-to-multipoint non-broadcast.

Point-to-multipoint non-broadcast is used in NBMA environments with virtual circuits of differing speeds".

Cisco says:

"Cisco IOS offers several options for configuraing OSPF so that it can overcome NBMA limitations, including the OSPF neighbor command, point-to-point subinterfaces, and point-to-multipoint. Which solutions are available to you depend on your NBMA network topology".

Does it mean form the above that we have two types of point-to-multipoint :

1- Broadcast (it does not say explicitly).

2- Non-broadcast (it does say expliciltly).

3- Cisco only mentions one type of point-to-mlutipoint (without specifing if it is broadcast or non-brodcast) ?

"Point-tomultipoint non-broadcast is used in NBMA environments with virtual circuits of differing speeds".

I did not get what did he mean here?

10 REPLIES
Gold

Re: point-to-multipoint and point-to-multipoint non-broadcast

There are four types of OSPF interface types:

38A(config-if)#ip ospf network ?

broadcast Specify OSPF broadcast multi-access network

non-broadcast Specify OSPF NBMA network

point-to-multipoint Specify OSPF point-to-multipoint network

point-to-point Specify OSPF point-to-point network

With brodcast, we send the hellos as a multicast, and elect a DR on the link. With non-broadcast, we expect each neighbor to be manually configured, send everything unicast (including hello's), and don't elect a DR. With point-to-multipoint, we send hellos and LSAs multicast, treat each adjacent neighbor as a point-to-point connection in the SPT, don't elect a DR, and inject /32's to provide reachability between the adjacent neighbors on this interface. With point-to-points, we treat the interface as a true point-to-point link.

HTH.

:-)

Russ.W

Gold

Re: point-to-multipoint and point-to-multipoint non-broadcast

"Point-tomultipoint non-broadcast is used in NBMA environments with virtual circuits of differing speeds".

I did not get what did he mean here?

--

BTW, this just means that most people recommend using the point-to-multipoint type of interface for multipoint interfaces where there are PVCs of different speeds. For instance, if you have a frame relay cloud with some PVCs with CIRs of 56k, and others with CIRs of 128k, etc. I normally tell people it all depends on the tradeoffs you want to make--manual configuration of all neighbors, making certain the hub router is always DR and handling remote-to-remote communications through manual mappings, or filtering out the /32's at the ABR....

:-)

Russ.W

New Member

Re: point-to-multipoint and point-to-multipoint non-broadcast

"With non-broadcast, we expect each neighbor to be manually configured, send everything unicast (including hello's), and don't elect a DR "

With non-broadcast I guess we do elect a DR,,,Am I right ?

Gold

Re: point-to-multipoint and point-to-multipoint non-broadcast

We do elect a DR with non-broadcast, I think I misspoke above. I just checked it in the lab.... This means you have to actually configure a full mesh of neighbors if you define a true broadcast link as a non-broadcast.

:-)

Russ.W

New Member

Re: point-to-multipoint and point-to-multipoint non-broadcast

As we know that we have point-to-multipoint non-broadcast,,,this is in Frame Relay environment because as we know that frame relay environment is NBMA.

What about point-to-multipoint broadcast (not non-broadcast),,,,where this type will be used ?

VIP Purple

Re: point-to-multipoint and point-to-multipoint non-broadcast

Hello,

network type point-to-multipoint broadcast does not exist. To avoid confusion, here are the 5 OSPF network types:

broadcast

non-broadcast

point-to-point

point-to-multipoint

point-to-multipoint non-broadcast

DR election only takes place with these combinations:

broadcast <-> broadcast

non-broadcast <-> non-broadcast

broadcast <-> non-broadcast

You can see this if you configure your interface with the ´ip ospf network´ command, only with ´broadcast´ and ´non-broadcast´ your output will look like this (issue the ´show ip ospf interface´ comamnd to see the output below):

Serial0 is up, line protocol is up

Internet Address 160.12.56.6/30, Area 0

Process ID 1, Router ID 6.6.6.6, Network Type BROADCAST, Cost: 64

Transmit Delay is 1 sec, State WAITING, Priority 1

No designated router on this network

No backup designated router on this network

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:09

Wait time before Designated router selection 00:00:29

With all other network types, you will not see the DR/BDR output, e.g. with point-to-multipoint non-broadcast:

Serial0 is up, line protocol is up

Internet Address 160.12.56.6/30, Area 0

Process ID 1, Router ID 6.6.6.6, Network Type POINT_TO_MULTIPOINT, Cost: 64

Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,

Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

Hello due in 00:00:12

HTH,

GP

New Member

Re: point-to-multipoint and point-to-multipoint non-broadcast

((network type point-to-multipoint broadcast does not exist. To avoid confusion, here are the 5 OSPF network types:

broadcast

non-broadcast

point-to-point

point-to-multipoint

point-to-multipoint non-broadcast ))

Thanks for that.

Now my concern about these two below only (two out of 5):

4- point-to-multipoint.

5- point-to-multipoint non-broadcast.

What is the difference between them ?

It makes sense for me that number 4 (point-to-multipoint non-broadcast) is used on Frame Relay environment; because Frame Relay (Layer 2) Technology is non-broadcast.

But what about number 5 (point-to-multipoint) what does it mean ?

Gold

Re: point-to-multipoint and point-to-multipoint non-broadcast

On point-to-multipoint, we use multicast hello's to discover neighbors (as if it's a broadcast link). While the keyword isn't in the network type command, OSPF treats the network as a broadcast capable multi-access link.

On point-to-multipoint non-broadcast, you must manually configured neighbors. Multicast packets will not be sent to discover neighbors.

Otherwise, they are the same.

:-)

Russ.W

New Member

Re: point-to-multipoint and point-to-multipoint non-broadcast

Thanks Russ

((Otherwise, they are the same.))

That means the point-to-multipoint,,,implicitly is broadcast,,,,isn't it ?

My second question is :

From Internetwork Expert Lab :

(((Hub and spoke and "ip ospf network" command

With Hub and spoke topology, If R2 is hub and R1, R3 are spokes,,,,and if the question ask :

1- Configure OSPF area 0 on the Frame Relay connection between R1, R2, and R3.

2- Do not use the "ip ospf network" interface command on R2.

The task above states that the "ip ospf network" command should not be used on R2,,,hat implies that OSPF network type that must be used on this segment is non-broadcast.))).

How does it imply ?

Gold

Re: point-to-multipoint and point-to-multipoint non-broadcast

If you configure a frame point-to-multipoint (NBMA) interface, the default OSPF network type is non-broadcast (which you would manually configure using the command ip ospf network-type non-broadcast, but which shows up in the router uutput as NBMA). So, yes, the problem is telling you to use non-broadcast type, which would imply that you must configure neighbors, or create point-to-point subinterfaces, or something....

:-)

Russ.W

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