From: Marvin Greenlee (mgreenlee@ipexpert.com)
Date: Sun Jul 13 2008 - 12:43:58 ART
The ospf distance command is used to manipulate distance for the router ID
of the router that is originating the network into OSPF, which is not always
the router that you received the update from.
In this case, if R1 is originating the network into OSPF, I wouldn't expect
changing distance for the router ID of 2 or 3 to have an effect for the
network from R1. In your output, you show config of 'distance 80', but none
of your debug shows an AD of 80. Do you have other distance commands
configured?
If R2 and R3 were border routers, and the connections between R1, R2, and R3
were a different process that both R2 and R3 were redistributing into a
process between R2, R3, and R4, then R2 and R3 would be the ones originating
the network into OSPF, and R4 could match based on the router ID of R2 or
R3.
Marvin Greenlee, CCIE #12237 (R&S, SP, Sec)
Senior Technical Instructor - IPexpert, Inc.
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
Mailto: mgreenlee@ipexpert.com
Progress or excuses, which one are you making?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
vatry2t@gmail.com
Sent: Sunday, July 13, 2008 5:04 AM
To: ccielab@groupstudy.com
Subject: OSPF distance change with same cost
Hi,
Imagine a router R1 connected to two routers (R2 and R3) and those two
routers
connected to a single fourth router (R4) (1 - 2 - 1 scenario). After
configuring OSPF, the R4 is load balancing routes originated on R1.
R1 lo0 is 10.1.1.1
R2 lo0 is 10.1.2.2
R3 lo0 is 10.1.3.3
R4 lo0 is 10.1.4.4
R4 routes:
O IA 10.1.1.1/32 [110/129] via 19.1.2.2, 00:12:59, Serial2/3 (through R2)
[110/129] via 19.1.3.3, 00:12:59, Serial2/2 (through
R3)
When I go to R4
access-list 1 permit 10.1.1.1
router ospf 1
distance 80 10.1.2.2 0.0.0.0 1 (to prefer route to R1 loopback 0
through
R2)
This is the output of debug ip routing
*Apr 15 23:25:39.789: RT: add 10.1.1.1/32 via 19.1.2.2, ospf metric [10/129]
*Apr 15 23:25:39.789: RT: NET-RED 10.1.1.1/32
*Apr 15 23:25:39.789: RT: add 10.1.1.1/32 via 19.1.3.3, ospf metric
[110/129]
*Apr 15 23:25:39.789: RT: NET-RED 10.1.1.1/32
It seems it is changing the administrative distance of the route learned
from
R2 but when you look at the routing table is still the same:
Routing entry for 10.1.1.1/32
Known via "ospf 1", distance 110, metric 129, type inter area
Last update from 19.1.3.3 on Serial2/3, 00:00:07 ago
Routing Descriptor Blocks:
19.1.2.2, from 10.1.2.2, 00:00:07 ago, via Serial2/3
Route metric is 129, traffic share count is 1
* 19.1.3.3, from 10.1.3.3, 00:00:07 ago, via Serial2/2
Route metric is 129, traffic share count is 1
If you look at the last update, it is coming from R3. If you shut down both
links from R4 to R3 and R2, first no shutdown link to R3 and then no
shutdown
link to R2, the distance of both learned routes is changed to 10 because the
last update is from R2 (which we have manually changed the administrative
distance)
Routing entry for 10.1.1.1/32
Known via "ospf 1", distance 10, metric 129, type inter area
Last update from 139.1.13.1 on Serial2/2, 00:00:01 ago
Routing Descriptor Blocks:
* 19.1.2.2, from 10.1.2.2, 00:00:01 ago, via Serial2/3
Route metric is 129, traffic share count is 1
19.1.3.3, from 10.1.3.3, 00:00:01 ago, via Serial2/2
Route metric is 129, traffic share count is 1
I have tried configuring all the routers on the same area, configuring
multipoint interfaces instead of point-to-point subinterfaces, configuring
traffic coming on different interfaces but the result is the same. Either it
keeps the metric unchanged on both paths or it changes to both paths,
depending
on which router it gets the last update from.
Could anybody help with that? It's driving me crazy.
Thanks for that!
This archive was generated by hypermail 2.1.4 : Mon Aug 04 2008 - 06:11:54 ART