From: Mike Haddad (mike.haddad@hotmail.com)
Date: Sat Mar 15 2008 - 04:29:10 ARST
Hello Malik,
OSPF uses SPF algorithm to calculate the route to destinations. SPF is
calculated in three phases. The first is the calculation of intra-area routes
by building the shortest path tree for each attached area. The second phase
calculates the inter-area routes by examining the summary LSAs and the last
one examines the AS-External-LSAs to calculate the routes to the external
destinations.
In your example, R2 will perform the SPF calculation on both received
summary routes and will choose the one that has the lowest metric => shortest
path. You can manipulate the route selection by many ways and one is by
increasing the OSPF Cost on the interface going to R3 so it uses R1 for the
summary.
Hope this helps,
Regards,
> Date: Sat, 15 Mar 2008 01:53:08 -0400> From: ccie.09@gmail.com> To:
ccielab@groupstudy.com> Subject: Route selection for Inter Area routes> >
All,> I would appreciate if some one can explain how inter area routes are>
selected in the following scenario> > R2 is receiving type-3 summary routes
from an ABR R1 in back bone area and> receiving the same route from R3 through
area say 10.> > > R2 & R3 are neighbors in area 10 and they both are part of
back bone also.> > Thanks> Malik> >
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