Re: Trying to understand OSPF Point-to-Multipoint Non-Broadcast

Hi Andrew,
Hub-spoke topology can better illustrate the point-to-multipoint
non-broadcast which is cisco proprietary.

This mode of operation seems strange at first glance because it uses static
neighbor peering using the neighbor command.

However, think of the use of the neighbor command that we can use in the hub
to solve the asymmetric cost to spokes.

Neighbor command can set the cost to the neighbor which allows better metric
control.

Regards,
Abdullah

On Sun, Jun 5, 2011 at 3:59 AM, Andrew LaPorte <andy_at_cloud9.net> wrote:

> Hi,
>
>
>
> I m hoping that someone can explain to me the way OSPF works on a
> Point-to-Multipoint Non-Broadcast.
>
>
>
> Let me explain the situation I m running across. I need to connect three
> routers using OSPF. The routers are:
>
>
>
> R1 fa0/0 (10.1.1.1/24) _-` fa0/0 (10.1.1.2/24) R2 fa0/1 (10.2.2.1/24) _ `
> fa0/1 (10.2.2.2/24)R3
>
>
>
> R1
>
> Interface fa0/0
>
> Ip add 10.1.1.1 255.255.255.0
>
> Router ospf 1
>
> Network 10.1.1.1 0.0.0.0 area 0
>
>
>
> R2
>
> Interface fa 0/0
>
> Ip address 10.1.1.2 255.255.255.0
>
> Interface fa 0/1
>
> Ip address 10.2.2.1 255.255.255.0
>
> Ip ospf network point-to-multipoint non-broadcast
>
> Router ospf 1
>
> Network 10.1.1.2 0.0.0.0 area 0
>
> Network 10.2.2.1 0.0.0.0 area 1
>
> Neighbor 10.2.2.2
>
>
>
>
>
> R3
>
> Inter fa 0/1
>
> Ip address 10.2.2.2 255.255.255.0
>
> Ip ospf network point-to-multipoint non-broadcast
>
> Router ospf 1
>
> Network 10.2.2.2 0.0.0.0 area 1
>
> Neighbor 10.2.2.1
>
>
>
> All connections are Ethernet. The restrictions given are that R2 to R3
> cannot form a DR/BDR relationship and they are not allowed to exchange
> multicast.
>
>
>
> My configuration is to use Point-to-Multipoint Non-Broadcast on the R2 to
> R3
> interfaces. When I do that I get a surprising result.
>
>
>
> I get 2 routes on R1 that are both /32 for 10.2.2.1 and 10.2.2.2 I m also
> not getting the /24 for the 10.2.2.0/24 that I m expecting.
>
>
>
> R1 show ip route
>
> O IA 10.2.2.2/32 [110/2] via 10.1.1.2, 00:00:34, FastEthernet0/0
>
> C 10.1.1.0/24 is directly connected, FastEthernet0/0
>
> O IA 10.2.2.1/32 [110/1] via 10.1.1.2, 00:01:07, FastEthernet0/0
>
>
>
> I m trying to understand why the /32 are showing up. My guess would be
> that
> the point-to-multipoint non-broadcast is causing the issue but I m just not
> sure.
>
>
>
> The second problem that I m trying to understand is why does the route for
> 10.2.2.0/24 not appear on R1.
>
>
>
> Any insight would greatly appreciated.
>
>
>
> Thanks,
>
>
>
> Andy
>
>
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Received on Sun Jun 05 2011 - 04:30:43 ART