OSPF filtering with administrative distance

Fellow experts,

I have a question on OSPF filtering with administrative distance.
I have a route to segment 155.1.67.0/24 injected in OSPF by 2 routers, R3 and
R6 as foll:

Rack1R5(config-router)#do sh ip o da sum 155.1.67.0

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Summary Net Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 318
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 155.1.67.0 (summary Network Number)
  Advertising Router: 150.1.3.3 <<< R3
  LS Seq Number: 8000005B
  Checksum: 0x97CB
  Length: 28
  Network Mask: /24
        TOS: 0 Metric: 2

  Routing Bit Set on this LSA
  LS age: 14 (DoNotAge)
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 155.1.67.0 (summary Network Number)
  Advertising Router: 150.1.6.6 <<< R6
  LS Seq Number: 80000001
  Checksum: 0x1B9D
  Length: 28
  Network Mask: /24
        TOS: 0 Metric: 1

The task says to send traffic from R5 to 155.1.67.0/24 towards R3, using AD.

I see 2 options here: either lowering the AD for this segment from R3 or
increasing the AD from R6.

I tried lowering the AD for 155.1.67.0/24 advertised by R3 but it did not
work!!! no matter what I did.

router ospf 1
 router-id 150.1.5.5
 log-adjacency-changes
 no discard-route internal
 area 0 range 150.1.0.0 255.255.252.0
 distribute-list prefix L0_R1_R2 in
 distance 50 150.1.3.3 0.0.0.0 10
 

A debug ip routing revealed that the AD for 155.1.67.0/24 received from R3
(150.1.3.3) was changed:

*Aug 19 09:00:58.929: RT: add 155.1.67.0/24 via 155.1.0.3, ospf metric [50/66]
 <<<<<<<<<
*Aug 19 09:00:58.933: RT: NET-RED 155.1.67.0/24
*Aug 19 09:00:58.933: RT: add 155.1.67.0/24 via 155.1.0.1, ospf metric [110/66]
*Aug 19 09:00:58.933: RT: NET-RED 155.1.67.0/24
*Aug 19 09:00:58.933: RT: SET_LAST_RDB for 155.1.79.0/24
  NEW rdb: via 155.1.0.3

But the routing table did not show this up. Here you are the result:

Routing entry for 155.1.67.0/24
  Known via "ospf 1", distance 110, metric 66, type inter area
  Last update from 155.1.0.1 on Serial0/0, 00:02:15 ago
  Routing Descriptor Blocks:
  * 155.1.0.3, from 150.1.3.3, 00:02:15 ago, via Serial0/0
      Route metric is 66, traffic share count is 1
    155.1.0.1, from 150.1.6.6, 00:02:15 ago, via Serial0/0
      Route metric is 66, traffic share count is 1

The only thing that worked was to set the AD to 255 for the segment
155.1.67.0/24 received from R6!!!

Rack1R5(config)#router ospf 1
Rack1R5(config-router)#no distance 50 150.1.3.3 0.0.0.0 10
Rack1R5(config-router)#distance 255 150.1.6.6 0.0.0.0 10

Rack1R5(config-router)#do sh ip rou 155.1.67.0
Routing entry for 155.1.67.0/24
  Known via "ospf 1", distance 110, metric 66, type inter area
  Last update from 155.1.0.3 on Serial0/0, 00:00:06 ago
  Routing Descriptor Blocks:
  * 155.1.0.3, from 150.1.3.3, 00:00:06 ago, via Serial0/0
      Route metric is 66, traffic share count is 1

Is this kind of a bug? Why this behavior??
I am on a 2611XM running IOS c2600-adventerprisek9-mz.124-17.bin

Thank you for your time to read this.

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Received on Sun Aug 23 2009 - 04:04:25 ART