From: Robert Rech (rjrech@xxxxxxxxxxxx)
Date: Wed Jul 24 2002 - 15:51:38 GMT-3
Some thing such as who's address space this is may effect you and if
your primary ISP is aggregating your subnets into a larger supernet that
is advertised outside of that ISP. This could cause a second ISP to
advertise you space with a longer prefix in which case prepending would
not do you any good.
You should look at your advertisements from an internet looking glass
outside of either of your ISP's if all the BGP entires are the same
prefix length then perpending would help and you might get some ideal of
how many times you should prepend your AS to the route path.
try some of the links at these sites.
http://www.merit.edu/~ipma/tools/lookingglass.html
http://nitrous.digex.net/
http://neptune.dti.ad.jp/
The route servers will give you a router console to run bgp cmds to
look at your ip space from someone else's perspective
Robert Rech
Senior Network Engineer
Cap Gemini Ernst & Young
Kansas City Service Center
rjrech@cgeykcsc.com
phone (816) 459-4767
fax (816) 459-6767
>>> Andre Teku <andre.teku@csosa.gov> 07/24/02 10:19AM >>>
If you are a stub (as opposed to a transit) do this:
1. Announce your aggregate or block of addresses to both ISPs but,
2. On the backup link announce your AS with a longer path length (use
the
prepend command) to make it less desirable
3. Take default route announcements from both ISPs but
4. On the backup link entry point assign a lower "Local Preference"
value to
the default route to make it unattractive
5. Don't take full routes and all that unless you want to optimize
neighborhood routing
Good luck
Andre
-----Original Message-----
From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
Sent: Wednesday, July 24, 2002 9:57 AM
To: Scooby Dooby
Cc: ccielab@groupstudy.com
Subject: Re: OT: Multihoming to two ISP's
What ?
Scooby Dooby wrote:
>
> A quick input:
>
> Wihtout running BGP and playing with the BGP attributes(Local
pref,Med and
> AS pre-pending), it would be unwise to advertise the same route
through
two
> different ISP's.
> It would cause routing loops ,
> as the world would have only one way to reach the main advertised
services
> like(Web,DNS,WEB) .Only ISP or company registered with IANA and
> RIR(regional registration authority)would be preferred to pass the
traffic
> to the end host.
>
> Cheers,
> OK.
>
> >From: Carlos G Mendioroz <tron@huapi.ba.ar>
> >Reply-To: Carlos G Mendioroz <tron@huapi.ba.ar>
> >To: ccielab@groupstudy.com
> >Subject: Re: OT: Multihoming to two ISP's
> >Date: Wed, 24 Jul 2002 07:22:17 -0300
> >
> >Conditional advertisement seems to be the only reliable way for
> >directing
> >all incomming traffic throw one link. And it also serves well the
health
> >of the core routers :-)
> >
> >
> >
> >roel.fonteyn@belgacom.be wrote:
> > >
> > > Did you try AS prepending, to reduce the chance other providers
taking
> >this route?
> > >
> > > Mvg/Rgrds,
> > >
> > > Roel
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