CCIE Pursuit Blog

May 14, 2008

Question Of The Day: 14 May, 2008

Topic: OSPF

r1 and r2 are running OSPF in area 0.  They have established a neighbor adjacency over a single serial interface.  Configure LSAs on both ends of this adjacency to set the DoNotAge bit.  Do not use the ‘ip ospf flood-control’ command.

r1#show ip ospf interface | i proto|Network Type
Serial1/0 is up, line protocol is up
  Process ID 100, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64

r1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  –        00:00:37    10.1.12.2       Serial1/0

r2#show ip ospf interface | i proto|Network Type
Serial1/0 is up, line protocol is up
  Process ID 100, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64

r2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  –        00:00:33    10.1.12.1       Serial1/0

Click Here For The Answer


Yesterday’s Question

Question Of The Day: 13 May, 2008 

Topic: OSPF

r1 and r2 are running OSPF in area 0.  They have established a neighbor adjacency over a single serial interface.  Configure LSAs on this adjacency to set the DoNotAge bit.

Answer:

r1 (or r2)
interface s0/0
 ip ospf flood-reduction

ip ospf flood-reduction

Reducing LSA Flooding

By default, an LSA will be refreshed every 30 minutes regardless if there are any changes in the network topology.  This is sometimes referred to as a ‘periodic’ or ‘paranoid’ update.  You can disable this update with the ‘ip ospf flood-reduction’ command.

Before:
r2
#show ip ospf database router 1.1.1.1 | i LS
  LS age: 153
  LS Type: Router Links
  LS Seq Number: 80000004


After:
r1
(config)#int s0/0
r1(config-if)#ip ospf flood-reduction

Real World Warning: This will reset your OSPF neighbor adjacency:

*Mar  1 00:09:28.623: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on Serial0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Mar  1 00:09:34.975: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on Serial0/0 from LOADING to FULL, Loading Done

r2#show ip ospf database router 1.1.1.1 | i LS
  LS age: 5 (DoNotAge)
  LS Type: Router Links
  LS Seq Number: 80000006

Whichever side of the link you configure this command on, it will affect the other side of the link.  In our example I applied the configuration on r1 only, so r2 is affected.  r1 is not:

r1#show ip ospf database router 2.2.2.2 | i LS
  LS age: 124
  LS Type: Router Links
  LS Seq Number: 80000004

If you need to affect both sides of the link, then you’ll need to apply it to both sides of the link.

There is at least one other way to accomplish this task….and that is today’s Question of the Day.  🙂

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2 Comments »

  1. […] Click Here For The Answer […]

    Pingback by Question Of The Day: 13 May, 2008 « CCIE Pursuit — May 14, 2008 @ 8:54 am | Reply

  2. a demand circuit could do the same job.

    Comment by ahenning — May 14, 2008 @ 2:33 pm | Reply


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