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 >> >> >> Blogs and organic groups at http://www.ccie.net >> >> _______________________________________________________________________ >> Subscription information may be found at: >> http://www.groupstudy.com/list/CCIELab.html > > -- > Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina Blogs and organic groups at http://www.ccie.netReceived on Fri Jan 04 2013 - 02:06:50 ART
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