Umesh,

Umesh_MS wrote:

> Hi..
> I have a doubt about the Nexthop calculation of virtual link.
> According to RFC the nexthop calculation of virtual link is deferred
> until the calculation of section 16.3..(section 16.1.1)
> What is the meaning of this...?
> Need to enter this candidate first without nexthop field(nexthop is a
> field in OSPF routing table) in routingtable.?..
> Then after the calculation of 16.3 we have to fill this field...is this
> right.?..
> Give me a clarification about this..
>

consider the following topology

R1------------R2--- Backbone
|
| Area 1
R3------------R4---Backbone

there is a virtual link between R3 and R2. since R3 has a virtual link R3
is ABR
when R3 will calculate the SPT for area 0 it will have a link ( type 4 ) to
R2 and from there a link to all the routers in the area 0.
since R2 is the only neighbor of R3 in area 0, R2 will learn all the
internal area 0 route and inter area route from R2 and the next hop of all
those destination will be the virtual link R2 however after step 16.3 in
which we consider the summary from non-backbone area ( transit area ) R3
might find a shorter path for internal area 0 route or inter area
destination through R4, therefore the actual nexthop for those destination
should be delayed until we have done the step 16.3
you can note that although we have a virtual link the actual path of a
destination may not follow the virtual link

Sina

>
> thanks in advance..
>
> Umesh M.S

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