More OSPF adventures with stuey

Unanswered Question
Mar 24th, 2009
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Well this is weird....or is it?


The backbone area is a 10.4.4.0/24 token ring segment; consisting of Routers F, G, H (whose RID's are 222.1.6.1, ...7.1 and ...8.1 respectively). Router F is the ABR to Area 1 via a serial link 201.0.0.0/30. (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 201.0.0.4 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 201.0.0.6; 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 201.0.0.4, 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 222.1.8.1"?? 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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Giuseppe Larosa Wed, 03/25/2009 - 02:58
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Hello Stuey,


1)


00:04:55: Processing link 0, id 201.0.0.4, link data 255.255.255.252, 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 201.0.0.4 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 201.0.0.4, link data 255.255.255.252, type 3

00:04:55: Add better path to LSA ID 201.0.0.7, gateway 201.0.0.4, dist 64

00:04:55: Add path: next-hop 201.0.0.6, interface Serial1

00:04:55: OSPF: Adding Stub nets

00:04:55: OSPF: insert route list LS ID 201.0.0.7, type 0, adv rtr 222.1.10.1

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


3)

00:05:03: OSPF: Detect change in LSA type 1, LSID 222.1.8.1, from 222.1.8.1 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

Giuseppe



CriscoSystems Wed, 03/25/2009 - 15:52
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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 (201.0.0.4) and the "type 0" referred to the broadcast (201.0.0.7). 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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