RE: OSPF LSA type 3 filtering

If you had 5000 routers in an OSPF area - you would have a CCDE (or navy seals) working over you very shortly after my report hit the CTO's desk - LOL

That would be a kludge design though

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Marko Milivojevic
Sent: Friday, January 04, 2013 5:07 AM
To: Carlos G Mendioroz
Cc: Brian McGahan; Narbik Kocharians; Cisco certification
Subject: Re: OSPF LSA type 3 filtering

What is missing is the decisive information on when you can stop computing. Without T2, there is no knowing when you are done :-). What if an area had 5000 routers.

You are correct though. You *could* do it without Type 2, but it can lead to dangerous issues.

--
Marko Milivojevic - CCIE #18427 (SP R&S)
Senior CCIE Instructor - IPexpert
:: This message was sent from a mobile device. I apologize for errors and brevity. ::
On Jan 4, 2013, at 2:02, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:
> Marko,
> say we have an area with 3 routers, R1, R2, R3, connected by a LAN.
> Then OSPF would choose one as DR. Say that lan is X.
> 
> Would you agree that the database representation would be:
> 
> Router links:
> R1: R1 -> DR (transit)
> R2: R2 -> DR (transit)
> R3: R3 -> DR (transit)
> 
> Net link:
> DR: X (R1,R2,R3)
> 
> You can draw the topology just by looking at the router links.
> What is missing ?
> 
> -Carlos
> 
> 
> Marko Milivojevic @ 04/01/2013 01:11 -0300 dixit:
>> Writing on a phone. Pardon the brevity
>> 
>>> 
>>> I would argue that you can make the topology of an area only with type 1 LSAs, and that type 2 LSAs are just for "condensing" the multiaccess
>>> link reachability information in one place.
>> 
>> Not quite. You would know which routers exist in the area, but not how they are interconnected.
>> 
>> To calculate the SPF tree, routers need two pieces of information for all non-leaf links: the link state, and relationship with other routers.
>> 
>> OSPF recognizes three link types in Type 1: stub, transit, and point to point.
>> 
>> For point to point links, link state is carried in two link state entries. Link itself is described as a "stub link", and the relationship with other router is described as a point-to-point link. These are both in Type 1 LSA.
>> 
>> However, for transit link the actual link is described as a link entry in Type 1 LSA, with a reference to a Type 2 LSA (in a form of a DR address). The Type 2 carries the topological information about the relationships between touters in the segment. Both are crucial for the topological calculation.
>> 
>> Note - this was all about the topological information and not the reachability.
>> 
>> -Marko
>> 
>> 
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> 
> -- 
> Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net