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

Hi Andrew,

Point-to-multipoint network types represent the shared link as a collection
of p-p links. Take a look at the router LSA on the hub and you will see two
p-p links with the same IP address, each connected to a different neighbor.
Since it is a collection of p-p, each host is represented as a /32. As far
as OSPF is concerned in that area there is no /24. One of the cool features:
on frame-relay spokes do not need maps to other spokes, all routes are
explicitly through the hub.

HTH,

-Bob Sinclair

> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Andrew LaPorte
> Sent: Saturday, June 04, 2011 9:00 PM
> To: ccielab_at_groupstudy.com
> Subject: Trying to understand OSPF Point-to-Multipoint Non-Broadcast
>
> Hi,
>
>
>
> Im hoping that someone can explain to me the way OSPF works on a
> Point-to-Multipoint Non-Broadcast.
>
>
>
> Let me explain the situation Im 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 Im
> also
> not getting the /24 for the 10.2.2.0/24 that Im 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
>
>
>
> Im 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 Im just
> not
> sure.
>
>
>
> The second problem that Im 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 Sat Jun 04 2011 - 21:21:07 ART