Hi

 If we needn't store the multiple paths,How are we
going to get the concept of pruning multiple entries
for ASBR in the routing table?
Please also explain me how this can be done...
--- Ash he <ash_heYAHOO.COM> wrote:
> Hi Xie,
>
> Will you not need to store multiple paths to
> implement equal-cost routing or traffic-load
> distribution?
>
> -Ash
>
> --- "Xie, Feng" <Feng.XieMARCONI.COM> wrote:
> > Hi, Nikhil:
> >
> > It is still not very clear to me why we need
> > to store multiple paths
> > to an ASBR. Please correct me if I am wrong. My
> > understanding is that an
> > ospf router only needs to keep the best route to
> an
> > certain ASBR according
> > to the rules specified in RFC2328 section 16. In
> > implementation, you can
> > choose to keep all routes to an ASBR and then
> choose
> > the best one every time
> > an external prefix is processed in SPF
> calculation.
> > Or you can only keep the
> > best route to an ASBR. Every time you receive a
> > different route to the same
> > ASBR, you compare it with the one you keep. If
> > better, replace the old one.
> > For me, the second one seems better.
> >
> > It is possible that multiple ASBRs advertise
> > the same external prefix.
> > Since there is a best route to each ASBR, you do
> > need to use the spec in
> > Section 16 to choose the best among them.
> >
> > Feng Xie
> >
> > -----Original Message-----
> > From: Nikhil Sama [mailto:Nikhil.SamaNEXSI.COM]
> > Sent: Thursday, August 23, 2001 1:58 PM
> > To: OSPFDISCUSS.MICROSOFT.COM
> > Subject: Re: About ASExternal calculation
> >
> >
> > Alex,
> > Actually you do keep multiple routes to a
> > router destination.
> > For instance, if an ASBR is reachable in
> > multiple area's via
> > different paths, you must store a routing table
> > entry for each path
> > regardless of cost.
> > It is only in the case of IP routes that
> you
> > store only the "best
> > route/routes" to a destination.
> > Nikhil
> >
> > "Xie, Feng" wrote:
> >
> >
> > Hi, Alex:
> >
> > Usually, we only keep the best route to a
> > destination. As you said, at
> > any time, there may be only one entry for an ASBR
> > with multiple next hops
> > due to equal-cost multipath. My understanding is
> > that what described in the
> > RFC is a process to build the best route to an
> ASBR
> > when you have choice
> > among multiple routes. It does not mean that an
> > implementation has to keep
> > all possible routes to an ASBR.
> >
> >
> > Feng Xie
> >
> >
> > -----Original Message-----
> > From: alex lerin [ mailto:alexlerinYAHOO.COM
> > <mailto:alexlerinYAHOO.COM> ]
> >
> > Sent: Thursday, August 23, 2001 5:43 AM
> > To: OSPFDISCUSS.MICROSOFT.COM
> > Subject: About ASExternal calculation
> >
> >
> > Hi..
> > I have a doubt in ASExternal Calculation...
> >
> >
> > In ASExternal calculations of RFC2328, Section
> > 16.4,3rd point 3rd paragraph,it says that if the
> > forwarding address is zero,th packet should be
> sent
> > to
> > the ASBR itself.Also it says that we have to prune
> > for
> > multiple entries.
> > My doubt is that how can we prune when there is
> > always only one entry for the ASBR in the routing
> > table.Because whenever we get a destination ,we
> > check
> > for its entry in the routing table and compare the
> > path type etc.,and if thay are equal cost we only
> > add
> > the next hop entry to the route and not a
> different
> > entry.So there is no possibility for multiple
> > entries
> > for the same ASBR in the routing table.
> > If I am wrong tell me when can there be more
> than
> > one entries for the same ASBR in the routing
> table?
> >
> >
> > Thanks in advance
> > Alex
> >
> >
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> > --
> >
> > Nikhil Sama E-Mail:
> > Nikhil.Samanexsi.com
> >
> > Routing Protocols Group Ph: 408 579 5880
> >
> > Nexsi Corp. Fax: 408 579 5701
> >
> > 1959 Concourse Drive Ph: (M) 310 428
> 9191
> >
> > San Jose, CA 95131. www.nexsi.com
> >
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> >
> >
>
>
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