Re: Communities

[Iljitsch van Beijnum <iljitsch () muada com>]

First, thanks to everyone who replied.

On Mon, 15 Oct 2001, E.B. Dreger wrote:

> For instance, I match "_asnthatIdontlike_" and penalize
> local-pref to [try to] avoid routing traffic over an ASN that
> I think has poor performance.  If I penalize AS65000, then

>       me 3549 65500 65432 65432 65432 65123

> will be preferred over

>       me 6347 65000 65123

> This is one reason that redistributing one's upstream routes via
> BGP can be bad despite as-path length:  If someone uses
> local-pref, it's quite conceivable that one will take the
> erroneous path that some edge idiot[1] leaked into the table.

I don't understand what you mean. Redistributing upstream routes
where/into what? How can this be "despite" as-path length?

> > And how about things like congestion?

> How do you mean?

Well, let me provide a real-world example. It's not really congestion, but
close enough for these purposes.

When Telehouse had problems in Manhattan after the attacks on September
11, one of our transit networks issued a warning that they might lose lots
or routes if the power would go down (which seemed likely at the time).
Since they use ATM, the BGP session to the router at the other side of the
connection would have to time out if this happened, creating a temporary
black hole. For us, the lost routes wouldn't be a problem, since we
multihome. But a black hole is a multihomer's worst nightmare.

So a community that indicates "you don't want to use this route unless you
absolutely have to--trust us" would have been very welcome. Such a
community would be especially useful in the face of congestion:
multihomers can route around the congested area and since some traffic is
rerouted the congestion would be less for the traffic that remains.

> > Is there any need for more "well known" communities?

> I wish that providers would set a community indicating route
> ingress.  I know, for instance, that GBLX does this... but their
> system with hundreds of communites leaves some to be desired,
> IMHO.

> I'd like to see providers tag "route learned in this region" at
> various granularity levels.

I would love to be able to see where a route originated and how bad the
detour getting here was.

But is it worth the trouble to try to "standardize" communities for this?

Iljitsch