Re: Addr: Re: BGP-4 - revised I-D

[Curtis Villamizar <[e-mail]>]

In message <v0300782aae444ba7b401@[152.160.213.42]>2]>, "John G. Scudder" writes:
> At 1:31 AM -0400 8/24/96, Curtis Villamizar wrote:
> >Proper MED handling wouldbe loop free.  The current BGP4 RFC allows
> >loops to be formed if a prefix is announced from 3 places by 2 AS all
> >announcing MED.
> >
> >MED clearly has to be changed.  The question is which of the two
> >proposed fixes to use.  Leaving the current loopfull MED is not
> >useful.  We've seen routing loops.
> 
> Ah, sorry.  I didn't make it clear that I don't consider any MED handling
> which can result in routing loops to be "proper".  I guess I have been
> convinced that what Rich calls an "election" is the right way to do MED.
> In fact RFC 1771 kind of says this, but in a very vague way:
> 
>    The MULTI_EXIT_DISC attribute may be used on external (inter-AS)
>    links to discriminate among multiple exit or entry points to the same
>    neighboring AS.  The value of the MULTI_EXIT_DISC attribute is a four
>    octet unsigned number which is called a metric.  All other factors
>    being equal, the exit or entry point with lower metric should be
>    preferred.  If received over external links, the MULTI_EXIT_DISC
>    attribute may be propagated over internal links to other BGP speakers
>    within the same AS.  The MULTI_EXIT_DISC attribute is never
>    propagated to other BGP speakers in neighboring AS's.
> 
> Note the clauses "same neighboring AS" and "all other factors being equal."
> 
> Anyway, I think that we're in violent agreement.
> 
> --John


Consensus seems to be leaning toward Rich's solution.  That's OK with
me.  It is harder to code since you can't simply compare the route
just learned with the current best route, you have to first compare
with the best route from the same AS, then compare to the overall
best route.  Still not terible.

Curtis