From: vatry2t@gmail.com
Date: Sun Jul 13 2008 - 06:03:37 ART
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