Ospf NSSA and Redistrubuting External routes into OSPF Domain

[mahesh18]

Hi All,

I was trying to implement OSPF  NSSA and Redistributing External routes into OSPF domain.

Router 1  is Directly connected to R2 with fas1/0.

Router 1

RIP config of R1

router ospf 1

router-id 5.5.5.5

log-adjacency-changes

area 2 nssa

redistribute rip metric 10 subnets

sh ip route

620Router#          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 192.168.3.2 to network 0.0.0.0

     172.16.0.0/24 is subnetted, 1 subnets

C       172.16.1.0 is directly connected, FastEthernet1/0

     10.0.0.0/24 is subnetted, 4 subnets

C       10.20.2.0 is directly connected, Loopback3

C       10.20.3.0 is directly connected, Loopback4

C       10.20.0.0 is directly connected, Loopback1

C       10.20.1.0 is directly connected, Loopback2

     192.168.3.0/31 is subnetted, 1 subnets

C       192.168.3.2 is directly connected, FastEthernet0/0

O*IA 0.0.0.0/0 [110/2] via 192.168.3.2, 00:01:13, FastEthernet0/0

2620Router#sh ip protocols

Routing Protocol is "ospf 1"

  Outgoing update filter list for all interfaces is not set

  Incoming update filter list for all interfaces is not set

  Router ID 5.5.5.5

  It is an autonomous system boundary router

  Redistributing External Routes from,

    rip with metric mapped to 10, includes subnets in redistribution

  Number of areas in this router is 2. 1 normal 0 stub 1 nssa  ************************************************

  Maximum path: 4

  Routing for Networks:

    10.20.4.2 0.0.0.0 area 3

    10.0.0.0 0.255.255.255 area 2

    192.168.3.3 0.0.0.0 area 2

  Routing Information Sources:

    Gateway         Distance      Last Update

    1.1.1.1              110      00:33:06

    4.4.4.4              110      00:33:06

    2.2.2.2              110      00:01:51

  Distance: (default is 110)

Routing Protocol is "rip"

  Sending updates every 30 seconds, next due in 17 seconds

  Invalid after 180 seconds, hold down 180, flushed after 240

  Outgoing update filter list for all interfaces is not set

  Incoming update filter list for all interfaces is not set

  Redistributing: rip

  Default version control: send version 2, receive version 2

    Interface             Send  Recv  Triggered RIP  Key-chain

    FastEthernet1/0       2     2

  Automatic network summarization is in effect

  Maximum path: 4

  Routing for Networks:

    172.16.0.0

  Routing Information Sources:

    Gateway         Distance      Last Update

  Distance: (default is 120)

sh ip ospf database on R1

             Type-7 AS External Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Tag

172.16.1.0      5.5.5.5         65          0x80000003 0x005852 0     ********************************************************Type 7

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag

0.0.0.0         4.4.4.4         1989        0x80000359 0x00093E 1

64.59.135.150   4.4.4.4         717         0x80000358 0x00DE40 0

172.16.1.0      5.5.5.5         68          0x80000002 0x005A7D 0 *********************************????????????????

Now this R1 router connects to ABR Router R3  which has connection to Area 0.

My question is that if R1 is advertising LSA type 7  to R3 then why R1 has route 172.16.1.0 as Type - 5 also  into its OSPF database.????????

As R3 has connection to Area 0 and it is supposed to redistribute 172.16.1.0 into OSPF domain as Type 5 --that part works fine in my LAB.

Here R3 is learning 172.16.1.0 route as Type 7

R3  -------------sh ip ospf database

                Type-7 AS External Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Tag

172.16.1.0      5.5.5.5         525         0x80000003 0x005852 0

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag

0.0.0.0         4.4.4.4         428         0x8000035A 0x00073F 1

64.59.135.150   4.4.4.4         1172        0x80000358 0x00DE40 0

172.16.1.0      2.2.2.2         645         0x80000001 0x004B77 0

172.16.1.0      5.5.5.5         2528        0x80000001 0x005C7C 0

Thanks

MAhesh

[Richard Burts · Accepted solution]

Mahesh

The router has 2 areas

Number of areas in this router is 2. 1 normal 0 stub 1 nssa  ************************************************

you have shown us area 2 as NSSA but it also has area 3 and I am guessing that area 3 is a normal area  and that is where the type 5 route comes from.

HTH

Rick

[mahesh18]

Hi Rick,

Thanks for reply.

But now i have shutown the OSPF area 3 between Router 1 and 2.

So it means even by shutting down link of OSPF area 3 it will remain in OSPF database?

Thanks

MAhesh

[mahesh18]

Hi Rick,

I did the clear ip route *  and clear ip ospf process on R1  so that Area 3 goes out of OSPF database.

So is there any way that we can take routes out of ospf database ?

OR i mean to say that OSPF dadatabse should be refresh as Area 3 is not connected to R1 router now?

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

Unfortunately Cisco IOS does not provide a command such as "clear ospf data" (I know that Junos does) .  One way to do this it is to delete the OSPF process and reinstall it or wait until LSA ages out which is about 1800 seconds.

HTH

[mahesh18]

Hi Reza,

Thanks for help again

I did exactly as you said -- delete router ospf 1.

Mahesh

[Richard Burts · Accepted solution]

Mahesh

I do not understand what you mean when you say that you shut down OSPF area 3. Can you clarify this?

If you have removed area 3 from the config I would expect that anything associated with area 3 would be removed from the OSPF data base and from the routing table.

Your question: "So is there any way that we can take routes out of ospf database ?" is slightly difficult to answer. My answer is that a basic principle of Link State routing protocols (like OSPF) is that if a neighbor sends a Link State Advertisement for a particular prefix, then that prefix must be in the OSPF data base. The only way to remove that entry in the OSPF data base is to go to the router which originated the advertisement and make that router make the prefix no longer an OSPF prefix.

I am not real happy with the way that I phrased this above, but I can not think of a better way to say it. I hope that it makes sense to you. The basic principle is that to remove an OSPF entry from the data base the router that originated the entry must withdraw it.

HTH

Rick

[mahesh18]

Hi Rick,

Thanks for reply and pointing me in right direction

Your first reply answered my question that route 172.16.1.0 was coming from Area 3.

This is what i did then to remove Route from Type 5 LSA.--------

From R1 i did no router ospf 1.

That made the OSPF database empty.e

Then i did not allow OSPF Area 3 between R1 and R2.

Here is Output from the R1 now

2620Router#sh ip ospf database

            OSPF Router with ID (5.5.5.5) (Process ID 1)

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         897         0x80000010 0x004DBD 2
5.5.5.5         5.5.5.5         580         0x80000012 0x0009F3 2

                Summary Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         2.2.2.2         897         0x80000006 0x00F236

                Type-7 AS External Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Tag
172.16.1.0      5.5.5.5         580         0x80000006 0x003F1B 0

Now it has Route 172.16.1.0 as only Type 7  not Type 5 LSA.

And R3 Router which connects to Area 0 has both Type 7 and Type 5  -- to advertise Type 5 into OSPF domain.

Many thanks again for Help.

Regards

MAhesh

[mahesh18]

Hi Rick,

Sorry i did not answer your ---question

.

Mahesh

I do not understand what you mean when you say that you shut down OSPF area 3. Can you clarify this?

By shutting down the Area 3  i meant that i shutdown the interface between R1 and R2 which was using OSPF Area 3.

Thanks

MAhesh

[Richard Burts]

Mahesh

Depending on the topology of the network sometimes shutting down an interface will remove entries in the OSPF data base (especially if that interface was the only way that route was learned). But sometimes shutting down an interface would not remove entries from the OSPF data base.

The best way to remove entries from the OSPF data base is to remove from the OSPF configuration the thing that generated the advertisement in the first place.

HTH

Rick

[mahesh18]

Hi Rick,

Thanks for your prompt reply again.

Regards

Mahesh