OSPF Network Type Point-to-Multipoint / Non-Broadcast, OSPF Per neighbor costs.

Lessons Learned:

Point-to-Multipoint Non-Broadcast

Same as point-to-multipoint, but sends hellos as unicast

--manually defined address with neighbor command

--Allows for per –VC OSPF cost over NBMA

No DR/ BDR Election

Special Next-hop processing

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Point-to-multipoint non broadcast –

We would want to use this where we have a partial mesh of layer 2 circuits But the underlying network is made up of different bandwidth values on the circuits.

Normally in a frame relay or ATM design.

For example: A frame relay cloud – hub and spoke and the VC’s are all different bandwidth speeds.

So the case where the main interface does not reflect the cost of the underlying circuits – that’s what Point-to-multipoint non broadcast is for.

Now – We can change the cost of the links – The cost value is part of the ospf calculation.

We can change the cost with an ospf neighbor statement under the interface and under the process we change  the cost with a neighbor statement.

Example:

R7#sh ip int brief | ex una

Interface                  IP-Address      OK? Method Status                Protocol

Serial0/0                  10.1.57.7       YES NVRAM  up                    up     

Serial0/1                  10.1.67.7       YES NVRAM  up                    up

The interface is currently point to point with a cost of 64

Serial0/0 is up, line protocol is up

  Internet Address 10.1.57.7/24, Area 10.1.0.0

  Process ID 1234, Router ID 10.1.67.7, Network Type POINT_TO_POINT, Cost: 64

  Transmit Delay is 1 sec, State POINT_TO_POINT

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

    oob-resync timeout 40

    Hello due in 00:00:08

  Supports Link-local Signaling (LLS)

R5(config)#neighbor 10.1.57.7 cost 128

R7#sh ip ospf interface serial 0/0

Serial0/0 is up, line protocol is up

  Internet Address 10.1.57.7/24, Area 10.1.0.0

  Process ID 1234, Router ID 10.1.67.7, 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

    oob-resync timeout 120

    Hello due in 00:00:26

  Supports Link-local Signaling (LLS)

  Index 1/1, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 10.54.4.5, cost is 128

  Suppress hello for 0 neighbor(s)

R7#

The cost of the link is 64 but the cost between the neighbors over that link the cost is 128 – basically the process level.

We could also use this network type on an Ethernet segment where the cost / links are different speeds going to the switch. Example 3 routers connected via a switch and all links are FA except one that is a 10MB Ethernet link.

If the links on the FA interface routers we’re network type broadcast, they wouldn’t be able to tell the difference between the 100 MB and the 10MBps. We can change it to point-to-multipoint and then change the cost value on a per neighbor basis.