[j-nsp] Load Balancing via BGP outbound at Colo

[Jesper Skriver]

On Thu, Mar 15, 2007 at 10:03:16PM +0100, Erdem Sener wrote:
> a little remark:
> 
> adding 'no-export' community to your advertised routes to ISP #x will
> guarantee that ISP #x won't advertise these prefixes to any of its
> ebgp peer, meaning "his peers won't use ISP #x to get to you".

It also means customer taking a full BGP feed from ISP #x, that
does not have a default route, may not have a route to you at all.

That will happen if they are single homes to ISP #x, either
permanently, or transiently while their connection to their other
ISP is down.

So in short, using 'no-export' is HIGHLY dangerous, and should be
used with great care - in fact I would strongly recommend not to
use it.

Instead prepend your advertisments to upsteams that you only want
to use as backup, and/or inquire with those providers, if they
have communities you can use to have them preprend when you
re-advertise your prefixes.

/Jesper
 
> On the other hand, this doesn't mean that ISP #x will certainly use
> its direct link towards you for your prefixes, since his route
> selection will be based on his own import rules (as-path, local pref
> etc.)
> 
> Also, it's always a good idea to check with a peer before sending out
> community information and to make sure he's not "resetting" it (using
> a import filter)
> 
> Cheers,
> Erdem
> 
> On 3/15/07, Chuck Anderson <cra at wpi.edu> wrote:
> > On Thu, Mar 15, 2007 at 02:28:20PM +0200, Tim Nagy wrote:
> > > You'd like to send and receive all traffic on the links to ISP #1 except for
> > > traffic that terminates in ISPs #2, #3, #10, or #20. Is that correct?
> > >
> > > For inbound, things are more complicated.  The only way that you can really
> > > influence your inbound traffic across multiple ISPs is through AS path
> > > prepending. You could advertise all of your routes to all ISPs, but prepend
> > > your AS multiple times to ISPs #2, #3, #10, and #20. That would reduce the
> > > traffic flow in from those ISPs and make your ISP #1 links the primary
> > > inbound points.
> >
> > You could also attach the well-known community NO EXPORT to routes you
> > send to ISP #2, #3, #10 and #20 so that those ISPs use your routes to
> > get back to you directly, but they won't readvertise your routes to
> > their upstreams and peers.
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> >
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/Jesper

-- 
Jesper Skriver, jesper(at)skriver(dot)dk  -  CCIE #5456

One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.