Umesh,

Umesh_MS wrote:

> Hello
>
> i have some doubts in summary LSA calculation of routing table...
> 1.any body can explain what will be the differnce between the 16.2 and
> 16.3 calculation of summary lsa in RFC 2328..

in section 16.2 we calculate the inter area route by examining the summary
LSA, note that an ABR Only consider the summary from
the backbone ( RFC 's ABR definition ).
in section 16.3 the ABR consider the "non-backbone" summary from transit
area in order to see if there is any better path than previously
calculated ( in section 16.2 only summary from backbone were considered )
this is explained clearly in section 16.3 and you have an example (
firgure 17).
here RT1 is an ABR an consider first the summary from the backbone (
virtual link ) generated by RT4 then by considering the non-backbone
summary from RT5 it will find a shorter path also note that if this step
is not performed we have a routing loop since RT1 goes through RT2 to
reach RT4 but RT2 goes through RT1 to reach RT5.

>
> 2.any way we for transit area also we will calculate using 16.2...then
> what is the difference...

see above also it is mentioned in the RFC

the purpose of the calculation below is to examine the transit
        areas to see whether they provide any better (shorter) paths
        than the paths previously calculated in Sections 16.1 and 16.2.
        Any paths found that are better than or equal to previously
        discovered paths are installed in the routing table.

        The calculation also determines the actual next hop(s) for those
        destinations whose next hop was calculated as a virtual link in
        Sections 16.1 and 16.2. After completion of the calculation
        below, any paths calculated in Sections 16.1 and 16.2 that still
        have unresolved virtual next hops should be discarded.

>
> 3. 16.3 is only for area border router's...

yes, and attached to the area with TransitCapbility set

>
> 4.when we have to generate summay lsa ...(Means after 16. 3
> calculation..?)

you generate a summary for the corresponding area or backbone when ever
you install route in your routing table if there is any change ( for
example shorter path found ) you regenerate the summary

Sina

>
>
> please give me solutions.
>
> thanks
> Umesh.M.S

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