OSPF Process ID need not match. Network Warrior sorta implies otherwise.

In this book, Network Warrior, the author says that you can redistribute routes between the multiple instances of spanning tree. I know that it is NOT a requirement for process IDs to match. Regardless of the PID's configured, all routers still learn all OSPF routes. Why does he say this about redistributing between OSPF processes? Was this the way things were with OSPF in the olden days?

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fsanyee

different instances can have different neighbors.

CodeBlox

Yeah, but they still learn all the same routes... Two routers that are not adjacent still eventually learn each others routes is what I'm saying. In the book, he's got a diagram with several OSPF running routers with matching PIDs like it's required that they match.

networker050184

Two OSPF processes on a router do not necessarily learn the same routes. I'm not familiar with the example you are referring to, but I'm assuming its a simplified approach to show the basics. The real world isn't always so clean cut.

As far as do they need to match, no but its a good idea to use the same number on all your routers. It makes mass configuration pushes much easier. You don't want to log in a router go to router ospf 10 and add a network then after 20 minutes of troubleshooting realize this router uses process 20.

CodeBlox

networker050184 wrote: »

Two OSPF processes on a router do not necessarily learn the same routes. I'm not familiar with the example you are referring to, but I'm assuming its a simplified approach to show the basics. The real world isn't always so clean cut.

As far as do they need to match, no but its a good idea to use the same number on all your routers. It makes mass configuration pushes much easier. You don't want to log in a router go to router ospf 10 and add a network then after 20 minutes of troubleshooting realize this router uses process 20.

Seems like they would. I can't think of a case where two OSPF processes don't but this could just be the newbie in me. I haven't seen this at work in the real world. His diagram has got PID 100 using routers on the left and PID 200 routers on the right. There is a sorta "Border Router" (no better term for it) that has both PIDs configured for OSPF. I fail to see how this would prevent the routers on the left from learning internal routes to those on the right and how redistributing would be required.

NetworkVeteran

CodeBlox, the CCNP Routing exam would probably clarify all this.

If you have:

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

If:
+ All routers are running OSPF.
+ B is running OSPF process 100 on network {B-left} and OSPF process 200 on network {B-right}.

Then:
+ B will have network {A-Left} in its RIB via OSPF process 100.
+ B will have network {B-Left} in its RIB because it's directly connected.
+ B's OSPF-200 LSDB will not have any info about networks {A-Left} or {B-Left}.
+ C's OSPF LSDB is identical to B's OSPF-200-LSDB. Thus, neither {A-Left} nor {B-Left} will be in its RIB.

EDIT - Note, I didn't mention A's or C's process-ids, because they are functionally irrelevant. However, I would strongly encourage using process-id 100 for router A and process-id 200 for router C to simplify troubleshooting.

fsanyee

Which diagram are you talking about CodeBlox? Give us a page no.

CodeBlox

Thanks for the explanation. I hadn't considered the fact that the network statements aren't configured in both processes so yeah... I see the need to redistribute between the two in this case as they don't learn each others routes (A and C). Don't see why one would run multiple OSPF processes though. CCNP is where I'm going next actually, looks like it could answer all of my questions.

As for the page, it's in the beginning of the routing protocol chapter. Let me get the page no.

CodeBlox

fsanyee wrote: »

Which diagram are you talking about CodeBlox? Give us a page no.

Page 103 and 104

NetworkVeteran

CodeBlox wrote: »

Don't see why one would run multiple OSPF processes though

Suppose you work for company Alpha, who just acquired company Omega, and both companies run OSPF across their internal networks. Your long-term goal may be to integrate the two network infrastructures, but your short-term goal may be to simply get them talking. This would be one of several interim solutions.