The MPLS-OPS Archive

[Puddinhead Wilson <puddinghead_wilson007@yahoo.co.uk>]

:)

and then we can run MPBGP/LDP etc inside the tunnel
and then we can make another tunnel between 2 new end
points and run MPBGP/LDP inside *that* tunnel....

Sounds like FUN!!
:)


--- Eric Osborne <eosborne@cisco.com> wrote: > On Tue,
18 May 2004 10:41:03 +0000, M. ELK
> <elkou141061@hotmail.com> wrote:
> 
> > Hi
> >
> > Despite it was explained to me previously still
> facing some difficulty.
> > Consider the following :
> >
> >
> > R1-a-----R2-----R3-----R4
> >
> > P1 prefix associated with R1 ,P2 with R2 ...etc .
> >
> > All link with 10 as cost . "a" is the interface of
> R1
> >
> > currently at R1 :
> >
> > Prefix      Cost    Via
> > P2           10       a
> > P3           20       a
> > p4           30       a
> >
> > Set T1 from R1 to R4 with absolute metric 1 :
> >
> > Case 1 :
> >
> > Prefix         Cost         Via
> > P2              10          a
> > P3              20          a
> > p4              1           T1
> >
> > Case 2 :
> >
> > Prefix      Cost    Via
> > P2           10       a
> > P3           11      T1
> > p4           1        T1
> >
> > Is it case 1 or case 2 (mainly for P3) ??
> 
> The details are probably going to be
> implementation-specific, but in the  
> case of the implementation I know the most about, it
> will be case 1.   
> Costs are changed *after* the IGP SPF is computed,
> which means that the  
> cost to p4 has no impact whatsoever on p2 and p3. 
> This is, of course,  
> assuming you are talking about our autoroute
> feature.  We have this other  
> thing, forwarding-adjacency, that doesn't behave
> like this at all, and  
> other vendors are free to do whatever they like with
> metrics.
> 
> > My guess it will be case 1 to follow
> draft-ietf-rtgwg-igp-shortcut-00.txt
> 
> I just looked at this draft, and it basically
> explains how our autoroute  
> works.  This leads me to believe that at least one
> other implementation  
> works basically the same way.
> 
> As an aside, the special case in section 5 of the
> draft looks a *lot* like
>
http://www/en/US/products/sw/iosswrel/ps1612/products_feature_guide09186a0080080850.html#1019729.
> 
> > , but what are the reason
> > to prefer this approach , is it to avoid any
> possible loop ??? If yes :  
> > could U pls provide an
> > example of topology where loop could exist .
> >
> 
> I've not seen too many people play with autoroute
> metrics; they are  
> confusing to most people, and tend to be used to
> solve the last 5% or 10%  
> of problems after you've applied lots of other
> tricks.  But that's just  
> me, others may have different exposure.
> 
> As far as loops, in the autoroute metric case there
> won't be any loops,  
> because of where the cost adjustment is done.
> 
> 
> 
> 
> eric
> 
> > .
> >
> > Now :
> > Config T2 from R4 to R1 with absolute metric 1 .
> > R1 and R4 are config to advertise T1,T2  as link
> in the IGP .
> >
> > at R1 :  could we expect that it is now case 2 ???
> .
> >
> >
> > Brgds
> >
> >
>
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