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

Hi Andrew,

OSPF will treat interfaces running point-to-multipoint or
point-to-multipoint non-broadcast as a series of point-to-point links with
one or more neighbors. Because OSPF views them as point-to-point, you will
see /32 host routes and not the /24 you may have been expecting.

OSPF point-to-multipoint and point-to-multipoint non-broadcast interfaces

On Sat, Jun 4, 2011 at 8:59 PM, 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 <http://10.2.2.2/24%29R3>
>
>
>
> 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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-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
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