Re: OSPF LSA type 3 filtering

With all due respect, this sounds like hand waving.

No matter how many routers you had, you would know of all that you have
access to, and without the T1 info of one, even if you knew it was
connected to the LAN, you could not use that info for anything useful.

Please provide one example of a dangerous issue.
In any case, I guess it is clear that T2 is not "only topological info".
That was my main point.

-Carlos

Marko Milivojevic @ 04/01/2013 07:06 -0300 dixit:
> 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

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net