IS-IS to OSPF Redistribution

[m-villas]

I am facing a problem while redistributing between IS-IS and OSPF. I try to explain you below

A--------B-----------C

A and C has 3 Physical (2Serial and 1Fastethernet) and a loopback interface. B has only 3 Physical interfaces and no loopback interfaces.

B and C are in same ISIS network so I made L2-only adjecency between them.

A has all its interfaces are completely in OSPF. B and C has all its interfaces in IS-IS.

On C I used passive interace loopback X to advertise loopback interaface. On physical interfaces I used ip router isis (Level-2 only).

On B I can see connected interfaces of C as IS-IS learned and vice-versa. Problem is as below

When I redistribute between ISIS and OSPF on B. Router A can see only IS-IS learned routes in B. I mean I cant see connected interfaces of B though I enabled ISIS and redistributed in to OSPF.

Any idea???

Tanks,

Martin

[m-villas]

Hi,

Correction....Adjecency is L1 only not L2.

I tried with L2 only too but same result. I could not see ISIS interfaces of Router B

Thanks,

Martin

[mark-obrien]

Martin,

A is not learning of the routes connected to B because your redistribution tells B to redistribute routes learned via IS-IS into OSPF. However, B does not learn of its connected routes via IS-IS, it sees them as connected. Have B redistribute "connected" into OSPF, with subnets, and A should learn of these networks.

HTH

Mark

[m-villas]

Mark,

But ISIS is enabled on the interface. If you see any other routing protocol like EIGRP, RIP and also OSPF....They redistribute if you enable routing protocol on it in to other protocol.

So you mean to say......While redistribution do we have to redistribute conencted networks always in addition to routing protocol?

Thanks,

Martin

[mark-obrien]

Martin,

Yes, any redistribution goes from the redistributing router's routing table - not a routing process's database - into the second protocol. Your router B will redistribute routes learned via IS-IS, shown as "i" in its routing table, to OSPF. B's routing table shows its connected networks as "C", not "i".

You have another option. You can run OSPF on B's connected interfaces. You can make them passive interfaces if you want.

HTH

Mark

[m-villas]

Mark,

You mean if I redistribute connected in router B, does all connected networks shows as with tag i instead of c? I dont think so.....Connected always have admin distance of 0 which is the lowest. So how connected interfaces vanishes and appear as learned from isis with the command redistribute connected.

Have you ever tried above? It is impractical and voilates the basic rules.

Thanks,

Martin

[mark-obrien]

No, the connected routes still show up as C in router B. I mentioned two different things here - redistributing connected networks into OSPF, and including B's connected networks in its OSPF configuration. These are two methods of getting B's connected networks advertised into OSPF. I've done this with other protocols, never IS-IS. It is very practical, and what rules does it violate?

Mark

[ruwhite]

So, the problem here is in the way IS-IS treats the IP routing table. Each route in the routing table has a set of markers that correspond to routing processes. So, for instance, a connected route is marked "C", so the routing table knows that route was inserted by, or is "owned by" a connected interface.

If a route is installed in the routing table by a given OSPF route, that OSPF process' marker will be attached to the route in the routing table. When the routing table displays routes, it uses this set of markers to determine what letter to put beside the route. If an ospf process installed the route, put an O out there, or an E1, or E2--as needed.

What normally happens when you configure a network statement which "covers" an interface on the router, is the process which now "owns" that route sets the marker in this data structure. Thus, while the route shows conencted in the output of show ip route, it has two markers, one for connected and one for the process with the network statement covering it. Since the connected marker has "higher precedence," it's the only one displayed. When you redistribute from this process to another routing process on the same router, it is picked up by the receiving process out of the routing table, since the route has been marked by the source process.

I hope this much makes sense.

IS-IS doesn't set these markers for local interface routes--only for routes IS-IS actually installs in the routing table. This makes sense, if you think about it, because IS-IS doesn't use network statements, it uses interface configuration commands to enable routing. The other protocols work through the routing table to determine which interfaces to run on, based on the entered network statement (excetpt BGP). IS-IS doesn't.

Does this make sense?

Russ.W

[m-villas]

Russ,

Thanks...It makes sense.

So do I have to redistribute conencted in ISIS to make these routes to appear in OSPF upon redistribution? or anythign else?

What exactly the command ip router isis in interface mode does......This comamnd does not enable ISIS Process on it?

Could just give a single URL on CCO for this?

Thanks,

Martin

[m-villas]

Russ,

...But my question is not answered. How do I get these conencted interfaces of Router B in to router A??? My customer doesnot agree to enable ospf on it though I enable passive interface on it.

He wants the interfaces should be in ISIS demarcation (This is a kind of boundary between 2 Vendors and I cant convince him on this)..........

Can somebody help me on this? How do I make it happen?

I built a test bed and tried hell lott of R and D but finally question is remains same.

Is there any solution for this question other than enabling OSPF on the interface?

Thanks,

Martin

[ruwhite]

Can't you use redistribute connected with a distribute list? OSPF and IS-IS are both already running on the box, right?

Russ.W

[m-villas]

Russ,

I tried redistributing connected in to ISIS but no use. Is redistributing the connected in to OSPF is the only solution other than enabling OSPF and making it passive? or any other way is possible?

I could not find a sample confiuration document even on CCO. I appreicate is you can send show me the URL for this kind of configuration.

Thanks alott,

Martin

[ruwhite]

There are two issues, most likely. Are you configuring a metric? Some routing protocols will pick up the metric for a redistribute connected from the local interfaces themselves, others won't. Try a metric ont he redistribute command. The second is that you cannot redistribute into an L1 routing domain, only an L2 routing domain, by default. You have to use the command:

redistribute connected level-1 metric 10

I'd still change to a single IS-IS process, as troubleshooting and maintaining two different IS-IS processes, one for level 1 routes, and one for level 2 routes, and then attempting to redistribute between the two, is going to be painful. In fact, you're going to end up having to run L1 on the L2 side anyway, since you have to have L1 routing to reach other routers within the L@ routing domain.

Russ.W

[m-villas]

Russ....Thanks and I apreciate your help

Tried with your guidelines but problem remains same.

Shall I conclude that there is no way to achieve the above via ISIS?

Appreciate anybody can help on this if you u come across this kind of problem...

Thanks,

Martin

[ruwhite]

Can you post your current configuration?

Russ.W