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[isp-bgp] Re: Multi-site BGP
This is one of the most misunderstood aspects of traffic shaping with
BGP. Your provider will, as often as not, set a local preference to
prefer the route directly received from you over an external path
regardless of AS-Prepends. Most providers do give you the option of
sending community strings to control the LocalPref of your route inside
their asn.
An Example.
An ISP I did some work for in Oklahoma wanted to load balance between a
Sprint and SBC connection. For Outbound traffic, they accepted full
tables and AS-Prepended sprint once as it came in. For Inbound traffic,
90% was coming from sprint in spite of 4 AS=Prepends. The solution was
to send a community to Savvis and SBC to set the localpref of the
advertised routes the same. This allows both routes to propagate, and
then you can fine tune with As-Prepends.
To Address the question posed at the start of this thread..
It is a good practice to use BGP as part of your disaster recovery
mechanisms. This eliminates waiting for DNS changes and Propagation in
the event of a failure. In this scenario, both sites would advertise
the same networks to your providers, with the backup site using a Low
localpref community. Traffic should never go to the second site unless
the first site withdraws its routes, (excluding provider issues). It is
poor form to have an ASN advertising the same networks and not have some
type of link between the two sites, but for a DR site you probably
already have that in place for database replication or whatnot.
Ejay Hire
CCNA,CCNP,CCDP
-----Original Message-----
From: Rich Pulver [mailto:pulverr@...Sent: Friday, January 31, 2003 8:11 AM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] Re: Multi-site BGP
I thought that if I just used path prepends in my DR site, I could
always
make the primary the best path (unless it went offline).
-----Original Message-----
From: Rick Macchio [mailto:rmacchio@...Sent: Friday, January 31, 2003 8:58 AM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] Re: Multi-site BGP
Couldn't you use MEDS or prepending to force inbound traffic toward one
site vs. the other? Or do you really need a conditional advertisement
to guarantee which path gets used in the inbound direction?
Thanks,
Rick Macchio
Michael Loftis wrote:
>
> No you can't just advertise the other site through BGP, because then
> packets could get delivered to other site depending on if it had a
better
> path or not...
>
> What you can do is a conditional advertisement...Take a look at the
> archives for this list, I seem to remember it being discussed very
recently.
>
> --On Thursday, January 30, 2003 4:20 PM -0500 Rich Pulver
> <pulverr@...> wrote:
>
> > Hello all. I have a question regarding BGP for Disaster Recovery.
Does
> > anyone use BGP currently for fail over to a DR site? If so, is it as
> > simple as advertising my networks through providers in both
locations
and
> > configuring the primary site as the preferred until that site goes
away?
> > (Or am I missing the fact that I won't be able to direct inbound
traffic
> > to such a degree?)
> >
> > This is what I have
> >
> > site1 - NY - Primary - 2 x T3 - 3 Class C from 1 provider - ASN with
ARIN
> >
> > site2 - CA - DR - 2 X T3
> >
> > I am already running BGP with two upstreams in NY. Can I just
advertise
my
> > routes and ASN in CA so all traffic will be redirected there if
anything
> > happens in NY? Are there any ramifications to this type of setup?
Any
> > input would be greatly appreciated. Thanks.
> >
> >
> > Rich
> >
> > _______________
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>
> _______________
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