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Re: a doubt on SPF
From: Acee Lindem (aceeREDBACK.COM)
Date: Mon Mar 24 2003 - 09:30:46 CST
Alok Dube wrote:
> Assume I have 2 ABRs...
> Area 1 connects to Area 0 via ABR-1 and ABR-2.
> my questions are as follows.
> 1. will ABR-2 learn the route to Area 0 via ABR-1 (network LSA)...i think
> it should..correct?
ABR-2 should use it's intra-area path to routes in area 0. This question is
a bit ambiguous due to the fact that there is no network diagram.
> 2. if the path to a destination is better via ABR-2----(router in Area
> 1)--ABR-1---area 0 routers---(ABR of other Area), it will take this
> route..compared to ABR-2 -- area 0 routers ---(ABR of other Area)...am i
OSPF Routers will prefer intra-area paths over inter-area paths.
> 3. if the destination was in Area 0 and the above condition again held
> true, there is no rule that a route learnt via type 1 lsa is given
> precedence over type 3?
> 3. Does OSPF ensure that routes learnt from a router are nevr sent back
> (split horizon types)...can someone point me to the part of RFC 2328 that
> states the same? or is the method implemented by means of simply checking
> the originator RID and discarding the LSA if it belongs to oneself?
This isn't needed for intra-area routes - the SPF calculation will
ensure there is no looping. For generated summary advertisements, one
doesn't advertise them back into the area corresponding to the route.
> 4. if there are 2 ABRs, how will the LSAs originated by ABR-1 be treated
> by ABR-2? which section of the RFC deals with this?..is page 135 line 1
> the answer?..but does the ABR itself use this LSA for its SPF
> calculations?(in a way this is same as case 1 above)
Read section 16.2 in RFC 2328. All the cases are covered.
> thanks and rgds