Exactly. Without T2, there is NP-Complete problem and there is no solution in finite amount of time. At least that's how people smarter than me explained it to me :-)
-- 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 2:21, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote: > Haha, no to the best of my knowledge. > > NP-complete is a kind of algo complexity. > > -Carlos > > Marko Milivojevic @ 04/01/2013 07:16 -0300 dixit: >> Btw. I believe the problem I was trying to describe is called NP-Complete, but that's a bit outside of my area of expertise. I'm not a mathematician not a CS. >> >> -- >> 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 2:06, Marko Milivojevic <markom_at_ipexpert.com> wrote: >> >>> 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 > > -- > 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 - 02:24:56 ART
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