RE: [nsp] OSPF quickie

From: Charles Sprickman (spork@inch.com)
Date: Wed Mar 28 2001 - 02:15:20 EST


On Tue, 27 Mar 2001, Martin, Christian wrote:

> Chales,
>
> Can you draw this out? Which side cannot see the other? Is the new split
> side connected to a LAN? Is there a DR election happening here?

           2xT1
          -------- router A
router C
           2xT1
          -------- router B

I simply moved "C" from "A" to "B" (no ip changes). A and B have
identical configs for ospf and the two serial interfaces. A and B are
connected via a T3 and speak OSPF. There were no changes made to C. C
sees routes via both T1's. B only sees routes via one T1.

'show ip ospf neigh detail' verifies that both links are up and exchanging
routes. Here's the brief output:

C:
Inch-Whitehall-gw>show ip ospf neighbor

Neighbor ID Pri State Dead Time Address
Interface
192.168.210.1 1 FULL/ - 00:00:36 192.168.200.205 Serial0/0
192.168.210.1 1 FULL/ - 00:00:36 192.168.200.201 Serial0/1

(here's a route learned from B)
Inch-Whitehall-gw>show ip route 192.168.198.0
Routing entry for 192.168.198.0/24, 2 known subnets
[...]
O E2 192.168.198.0/26 [110/20] via 192.168.200.201, 1d11h, Serial0/1
                         [110/20] via 192.168.200.205, 1d11h, Serial0/0

B:

core-2>sh ip ospf neighbor

Neighbor ID Pri State Dead Time Address
Interface
192.168.210.4 1 FULL/ - 00:00:32 192.168.200.202 Serial2/0
192.168.213.1 1 FULL/ - 00:00:39 192.168.200.65 Serial4/0
192.168.210.4 1 FULL/ - 00:00:33 192.168.200.206 Serial5/0/1:0
(2/0 and 5/0/1 are the two T1's)

(here's a route learned from C - only one path)
core-2>show ip route 192.168.192.0
Routing entry for 192.168.192.0/24, 4 known subnets
  Variably subnetted with 4 masks
  Redistributing via ospf 1

O E2 192.168.192.128/30 [110/20] via 192.168.200.202, 1d11h, Serial2/0
O E2 192.168.192.64/27 [110/20] via 192.168.200.202, 1d11h, Serial2/0
O E2 192.168.192.96/28 [110/20] via 192.168.200.202, 1d11h, Serial2/0

Any ideas? Sorry for all the clutter, I was hoping that putting all this
info together would help me see the problem...

Thanks,

Charles

> chris
>
> > -----Original Message-----
> > From: Charles Sprickman [mailto:spork@inch.com]
> > Sent: Tuesday, March 27, 2001 11:52 AM
> > To: cisco-nsp@puck.nether.net
> > Subject: [nsp] OSPF quickie
> >
> >
> > Hi,
> >
> > Small OSPF problem that's got me scratching my head... I just moved a
> > connection from one router to another (two T1's). Both the previous
> > router these went back to and the new one are in the same
> > ospf area, and
> > I've verified that all the neighbors see each other.
> >
> > On the old router, I was seeing routes from the remote side
> > via both T1
> > connections, which gave me a sort of load-balancing between
> > the two lines.
> > On the new router, even though I see the remote side listed
> > as a neighbor
> > twice, I only see routes via one T1.
> >
> > OSPF config is identical on both routers, is there a global switch I'm
> > missing somewhere? I know this is something silly and
> > obvious, but I'm
> > not seeing it... Old router is running 12.0.7T, new is 12.0.7XE1.
> >
> > Thanks,
> >
> > Charles
> >
> > | Charles Sprickman | Internet Channel
> > | INCH System Administration Team | (212)243-5200
> > | spork@inch.com | access@inch.com
> >
>



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