From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Wed Aug 06 2003 - 14:03:45 GMT-3
Even though the routers are "adjacent" they won't become true neighbors
with each other. By adjusting the hello/dead timers you can make any
OSPF network type become adjacent but that doesn't mean they will become
functioning OSPF neighbors.
OSPF network types that use a DR (broadcast and non-broadcast) can
neighbor with each other and function properly. Likewise OSPF network
types (point-to-point and point-to-multipoint) that do not use a DR can
neighbor with each other and function properly. But if you mix DR types
with non-DR types they will not function properly. You should see in the
OSPF database "Adv Router is not-reachable" messages when you've mixed
DR and non-DR types.
Here is what will work:
Broadcast to Broadcast
Non-broadcast to Non-broadcast
Point-to-point to Point-to-point
Point-to-multipoint to Point-to-multipoint
Broadcast to Non-broadcast (adjust hello/dead timers)
Point-to-point to Point-to-multipoint (adjust hello/dead timers)
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Wednesday, August 06, 2003 6:10 AM
To: Group Study
Subject: Surprise Result -- OSPF nei are adjacent but don't exchange
link states
Good Morning,
I just configured 2 ospf routers with different ospf net types
On R2's s0, I configured p2m.
On R3's s0, I left it at default (non-broadcast for physical F/R).
Result:
There was an election for the DR (R2 won - it had the higher
router-id).
R2 and R3 became adjacent and exchanged the link state database, but, R2
and
R3 didn't add any of the routes to the route table that they had learned
from
each other. Note: a check of the ospf link state database on R3 showed
that
it had learned of all the routes from R2 and vice versa.
When I change R3's s0 back to ospf net type, the route tables on both R2
and
R3 both show all the routes that were exchanged.
Questions:
Why do R2 and R3 become adjacent even though they have different ospf
net
types?
Why is there a DR/BDR election between R2 and R3 when R3 has an ospf net
type
of "non-broadcast"?
Why doesn't R3 add the routes it learns from R2 if it's adjacent to R2?
I thought that that R2 and R3 wouldn't become adjacent since they had
different net types but if they did become adjacent, then they would add
the
routes they learned from each other. Is this behavior to be expected or
is
there something else going on?
Thanks in advance, Raj
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