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More OSPF adventures with stuey

Well this is weird....or is it?

The backbone area is a token ring segment; consisting of Routers F, G, H (whose RID's are, ...7.1 and ...8.1 respectively). Router F is the ABR to Area 1 via a serial link (Router A is at the other end and there's nothing else in Area 1.)

Router H, meanwhile is the ABR to Area 2; via the serial network. Router J is at the other end of that link and there is nothing else in that area.

Router J was the last to join, because I wanted to witness the arrival of Type 3 LSA's from the backbone. I booted up Router J, configured it (Serial 1 is; obviously .5 at Router H's end) for OSPF, enabled debug ip ospf spf (intra, inter, and external), and finally enabled the interface.

The debug output is in the attached .txt file.

My questions are these:

1. On line 3, what does "type 3" refer to? It can't (in my mind) refer to the LSA type, because a)later on, there's a type 0; and b)the link is, to which the router is directly connected. Why would an area-internal route appear as a Type 3 LSA?

2. On line 7, what does "type 0" mean?

3. Why is it ever saying "ABR not reachable"?? That router is its only neighbor, the only reason it's even getting LSA's. Why would it be called " not reachable?"

4. I notice there is a "delete list." What are the criteria for being placed on the delete list; and why are so many of the routes/links that Router J is first learning about being placed on the delete list so promptly?

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Re: More OSPF adventures with stuey

Hello Stuey,


00:04:55: Processing link 0, id, link data, type 3

A router LSA actually contains multiple links, each link has a link-id and a link type:

so here we have link 0 id link type 3.

2) nice question looks like an error in debug output the type cannot be 0 (it could be a O for intra-area route ???)

00:04:55: Processing link 0, id, link data, type 3

00:04:55: Add better path to LSA ID, gateway, dist 64

00:04:55: Add path: next-hop, interface Serial1

00:04:55: OSPF: Adding Stub nets

00:04:55: OSPF: insert route list LS ID, type 0, adv rtr

00:04:55: OSPF: Entered old delete routine


00:05:03: OSPF: Detect change in LSA type 1, LSID, from area 2

a change in router lsa of the ABR is happened, after the message I've reported just above the error message is not listed anymore

Hope to help


Re: More OSPF adventures with stuey

Thanks, Giuseppe.

1) So does link-type 3 mean broadcast link, or what? Is there a chart of the different link-type values I can refer to?

2) It's definitely a zero; not a letter "O" so I am still confused. One thing I noticed is that the "type 3" link referred to the network address ( and the "type 0" referred to the broadcast ( Am I on to something?

3) Yeah I saw it detect the "change" in the LSA to the ABR; but I still don't understand why the ABR was ever showing up as unreachable. Ever. At all.

OSPF is complicated!!!

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