OSPF Redistribution Question

[bdb_opteman]

Hi,

When redistributing routes from one OSPF process to another on the same router with no route maps filters, etc, shouldn't you see the same routes in the type 5 section of the LSDB?

Our LAN routes come into our service provider's router as external routes in OSPF process 1.  The router also has OSPF 6 set up for redistribution into BGP. 

It's set up like this:

router ospf 6

redistribute ospf 1

(passive interface & network statements left out)

router ospf 1

passive-interface default

no passive-interface G0/1

network 1.2.3.4 0.0.0.255 area 1

(etc...)

When I do a show ip ospf database, I see all the LAN routes in OSPF 1 under Type-5 AS External Link States (they are redistributed from another area in the LAN).

However, when it gets down to process 6, I don't see them.

Is something stopping them from redistributing or is this expected behavior?  I would expect to see the routes listed in the LSDB of both processes if they're being redistributed from one process to the other.

Thanks!

-Stacy

[Peter Paluch]

Hi Stacy,

Perhaps the OSPF 6 process redistribution is missing the subnets keywords, i.e.

router ospf 6

  redistribute ospf 1 subnets

Indeed, if routes have been imported into an OSPF process via redistribution, they should be visible as LSA-5. Please note, however, that redistribution is performed based on the routing table and not on LSDB contents - that means that even redistribution from OSPF 1 to OSPF 6 does not simply retake the LSA-5 from one LSDB to another, but rather, the router looks up the routes from OSPF 1 installed into the routing table and subsequently imports them as LSA-5 into OSPF 6. So beware of the dependency: the redistribute ospf 1 subnets redistributes only those routes that have been originally inserted into the routing table by OSPF 1.

Best regards,

Peter

[bdb_opteman]

Peter,

You are right in that the subnets keyword is missing.  The routes I'm looking at are mostly /24 subnets of a 10.x.x.x network so that would make sense. 

Very good reminder about taking the routes from the routing table.  One of the routes I'm looking at as a test case is in fact in the routing table known via ospf 1.  The strange thing is, it also says "Redistributing via ospf 6".  I'm not sure if that only means redistribution is set up between the processes or if it successfully redistributed the route.  It's not in the process 6 LSDB however.

I think your suggestion about the subnets keyword is on they money.  This may be by design. 

[Peter Paluch · Accepted solution]

Hello Stacy,

Surely, without the subnets keywords, the /24 subnets of a 10.x.x.x network will not be redistributed into OSPF 6 no matter what.

The strange thing is, it also says "Redistributing via ospf 6".  I'm not  sure if that only means redistribution is set up between the processes  or if it successfully redistributed the route.

I do not know exactly, either, but I have a feeling that it simply says that the redistribution has been configured. It does not mark individual routes as being redistributed indeed.

Best regards,

Peter

[bdb_opteman]

Thanks for looking at this!

-Stacy