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2016
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Beginner

OSPF Redistribution Question

Router A is an ASBR in a NSSA. Redistributing routes from RIP into OSPF which includes a default route.

Router B is the ABR between the NSSA and Area 0. It receives all the redistributed routes as LSA Type 7.

Router C is another ABR between Area 0 and Area 1. It receives all the redistributed routes from Router A as LSA Type 5. . . bar the default route. The Link State Database has no record of an LSA for the default route.

Is this normal operation? I need a categorical answer on this please.

If it is normal operation, is the 'default-information originate' command required on Router B?

Thanks

Everyone's tags (4)
23 REPLIES 23
Hall of Fame Cisco Employee

OSPF Redistribution Question

Hi Nigel,

A default route cannot be redistributed into Cisco's implementation of the OSPF protocol. In other words, the default route from RIP will not be redistributed to the OSPF database on Router A while other RIP routes will. The only way to inject a default route into OSPF is to use the default-information originate command in regular areas, or using the command area X nssa default-information-originate in NSSA areas, where X is the area number.

Therefore - yes, this is a normal behavior for Cisco OSPF.

In your case, the area X nssa default-information-originate command should be used on the Router A.

Best regards,

Peter

Beginner

OSPF Redistribution Question

Hi Peter

Thanks for the reply.

What I'm observing doesn't fully tally with your explanation. It might just be that you confused the routers in your explanation - Router A and B.

I do see the default route in the ospf routing table in Router A and Router B. Router B has the default route as an LSA Type 7 in its LSA Database and the default route is in its routing table. It's just Router C that doesn't see it!

To clarify, Router A is connected to the RIP domain and the NSSA Area - let's call it Area 2.

Router B is the ABR between Area 2 and Area 0

Router C is an ABR between Area 0 and another area - we'll call it Area 1.

So it appears that the default route is being redistributed but being stopped at Router B - the ABR between the NSSA and Area 0. So the area x nssa default-information-originate command should be configured on Router B and not Router A?

Hall of Fame Cisco Employee

OSPF Redistribution Question

Nigel,

This is strange because I have verified my config on 2691 IOS and a default route learned via RIP is not being redistributed into OSPF, not even in a NSSA area.

Can you post the OSPF configuration from the Router A, plus its routing table and its LSA database output?

Best regards,

Peter

Beginner

OSPF Redistribution Question

I will get this for you. What you're not going to like is that up until a week ago Router C was seeing the default route as a Type 5 in its LSA Database and thereby it got populated into its routing table! No config changes made and now Router C isn't seeing it.

I'll get the configs asap.

Hall of Fame Cisco Employee

OSPF Redistribution Question

Nigel,

Thanks - unfortunately, for upcoming 3 hours, I will be off. I'll get back after that - in the meantime, perhaps some of other friends here will take over.

Until then!

Best regards,

Peter

P.S.: Yes, you are right - I don't like it

Hall of Fame Guru

Re: OSPF Redistribution Question

Nigel

So the area x nssa default-information-originate command should be configured on Router B and not Router A?

No it should be configured on router A ie. the one doing the redistribution between RIP and OSPF.

I have just labbed this up to confirm and as Peter said without the area x nssa default-information-originate command you should not see a default-route on either B or C.

Jon

Beginner

OSPF Redistribution Question

Thanks. I'm still waiting on the configs from a colleague. However, we may be able to settle this without the configs. It may be that the area x nssa default-information-originate command is there on Router A. Won't know until I get the configs.

The real question is how do I get Router C to see the default route and get it into its routing table?

Nigel

Hall of Fame Guru

OSPF Redistribution Question

Nigel

Once the "area x nssa default-information originate" command is applied on A then the default-route should be in router C's routing table.

Jon

Beginner

OSPF Redistribution Question

But it isn't. We see it in Router B but not Router C.

So if the 'area x nssa default-information-originate' command is on Router A then the fact that Router C doesn't see the default route I can conclude that I have a genuine issue?

Hall of Fame Guru

OSPF Redistribution Question

Nigel

Yes, if you cannot see it on Router C you have an issue.

We need to see the configs really to be sure.

Jon

Hall of Fame Cisco Employee

OSPF Redistribution Question

Jon and Nigel,

Jon, thanks for taking this issue up while I was unavailable. I hope you'll stay active in this thread - the issue seems to be quite intriguing.

Nigel, the configuration on router A plus the output of its link-state database will be crucial.

Best regards,

Peter

Frequent Contributor

OSPF Redistribution Question

Can you also get the "show ip ospf database nssa-ext" output from the Router B ( ABR for NSSA ) . As far as the nssa default-information-originate command is concerned , it should be on the Router A as Jon & Peter already mentioned.

If the command  " area XX nssa default-information-originate" is configured on the Router B in your case then you will see the default route being propagated in the NSSA as type 7 even if the Router B does not have that route in its routing table. but the output of the above command will show you that "NO TYPE 7/5 TRANSLATIONS" .

Manish

Hall of Fame Cisco Employee

OSPF Redistribution Question

Manish,

but the output of the above command will show you that "NO TYPE 7/5 TRANSLATIONS" .

Hmmm, correct me if I am wrong but this line should not be related to the area X nssa default-information-originate command at all. A NSSA area has only one router performing the 7-to-5 translation, even if it has multiple ABRs. As per RFC 3101, the translator is the ABR with the highest RID. Other ABRs will not be 7-to-5 translators and will produce th e output similar to yours.

That is how I have always understood this indication.

Best regards,

Peter

Frequent Contributor

OSPF Redistribution Question

Here an example :-

1> Cisco's example where the ABR does not have the default route but is still origanating the default info in the NSSA , the output shows "NO type 7/5 translation"

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9fa.shtml#exam

2> some other example :-

where the originate command is on the ASBR , the ABR shows 7/5 translation in options field :-

http://wiki.nil.com/External_default_route_in_NSSA_area

I hope I understood it well ;-)

Manish

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