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OSPF database and subnets

Hi,

If we have many routers in OSPF area 0 and dont have access to all of them. We know the router ID, is it possible to know which subnets that particular router is publishing from ospf databse.

Those subnets are available in the routing table- traceroute also shows from where those are coming from.

May be very basic but still I am not able to find.

Thanks

Subodh

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: OSPF database and subnets

Hello Subodh,

there are several options in sh ip ospf database

sh ip ospf database ?
  adv-router        Advertising Router link states
  asbr-summary      ASBR summary link states
  database-summary  Summary of database
  external          External link states
  network           Network link states
  nssa-external     NSSA External link states
  opaque-area       Opaque Area link states
  opaque-as         Opaque AS link states
  opaque-link       Opaque Link-Local link states
  router            Router link states
  self-originate    Self-originated link states
  summary           Network summary link states
  |                 Output modifiers

you can use sh ip ospf database router 1.1.1.1

to see the router LSA generated by advertising router 1.1.1.1

if you do sh ip route 10.2.1.0 and you look at the from field you should see the OSPF router-id of the router that injected the LSA in the OSPF domain.

Hope to help

Giuseppe

5 REPLIES

Re: OSPF database and subnets

Hi,

Yes. This is possible.

router#sh ip ospf database adv-router

Regards

Karuppu

New Member

Re: OSPF database and subnets

Hi

I created small topology in test lab R1 and R2

R1 - Serial link ( 10.1.1.0 /30 ) ---- R2

and R1 : has fa0/0 - 10.2.1.0 /24

R1 - RID = 1.1.1.1

R2 -RID = 2.2.2.2

here is the output :

R2#sh ip os neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  -        00:00:30    10.1.1.1        Serial1/0
R2#

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O       10.2.1.0/24 [110/65] via 10.1.1.1, 00:04:16, Serial1/0 ( It has learned 10.2.1.0 / 24 subnet )
C       10.1.1.0/30 is directly connected, Serial1/0
R2#

Now how can I find the advertised subnets from R1 ( RID = 1.1.1.1 ) from ospf database

Here is the output :

R2#sh ip os database adv-router 1.1.1.1

            OSPF Router with ID (2.2.2.2) (Process ID 10)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         339         0x80000003 0x00C598 3                       ( no subnets seen here )
R2#

R2#sh ip os database

            OSPF Router with ID (2.2.2.2) (Process ID 10)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         589         0x80000003 0x00C598 3
2.2.2.2         2.2.2.2         596         0x80000002 0x000B6D 2
R2#

This doesnt show any subnet that is advertised by 1.1.1.1.  How to find out that RID 1.1.1.1. router is publishing the subnet 10.2.1.0 / 24 ( in our case ) from ospf database?

Thanks

Subodh 

Hall of Fame Super Silver

Re: OSPF database and subnets

Hello Subodh,

there are several options in sh ip ospf database

sh ip ospf database ?
  adv-router        Advertising Router link states
  asbr-summary      ASBR summary link states
  database-summary  Summary of database
  external          External link states
  network           Network link states
  nssa-external     NSSA External link states
  opaque-area       Opaque Area link states
  opaque-as         Opaque AS link states
  opaque-link       Opaque Link-Local link states
  router            Router link states
  self-originate    Self-originated link states
  summary           Network summary link states
  |                 Output modifiers

you can use sh ip ospf database router 1.1.1.1

to see the router LSA generated by advertising router 1.1.1.1

if you do sh ip route 10.2.1.0 and you look at the from field you should see the OSPF router-id of the router that injected the LSA in the OSPF domain.

Hope to help

Giuseppe

New Member

Re: OSPF database and subnets

Hi,

Thanks a lot I connected third router in cahin.

R1 ---> R2 -----> R3

R1 has 10.2.1.0 /24 network.

On R3

R3#sh ip route 10.2.1.0
Routing entry for 10.2.1.0/24
  Known via "ospf 10", distance 110, metric 129, type intra area
  Last update from 10.1.1.5 on Serial1/0, 00:00:41 ago
  Routing Descriptor Blocks:
  * 10.1.1.5, from 1.1.1.1, 00:00:41 ago, via Serial1/0  (   this router is injected by R1 RID 1.1.1.1 )
      Route metric is 129, traffic share count is 1

R3#

Thanks again.

Subodh

Hall of Fame Super Silver

Re: OSPF database and subnets

Hello Subodh,

>> * 10.1.1.5, from 1.1.1.1, 00:00:41 ago, via Serial1/0  (

I was referring exactly to this part of sh ip route output with from field

Hope to help

Giuseppe

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