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List:       isp-bgp
Subject:    [isp-bgp] RE: Disapearing prefix problems
From:       "Ejay Hire" <ejay.hire () isdn ! net>
Date:       2003-06-30 16:59:31
[Download RAW message or body]

Set the localpref of the advertisement to below default in your AS.  This way, you will hear and use the at&t path.  With bgp, you normally advertise only routes you use, so you will either not announce the route at all, or announce the at&t path.  (depending on how your egress filters are setup.)

Ejay

-----Original Message-----
From: Chad Monteith [mailto:chadlist@tspec.net]
Sent: Friday, June 27, 2003 12:13 PM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] RE: Disapearing prefix problems


That's the problem...

Both the end users router and mine are advertising the 7018:20 community
to AT&T.  if I go to their route server I see it without a problem.

I'm not even wanting to load balance for the most part.  Since our link
is metered they want all traffic both incoming and outgoing to
transverse via their existing AT&T T1 instead of the metered link they
have to us.  When I start advertising their prefix almost all incoming
traffic comes to them via me instead of AT&T.

I've had no problem in getting outbound to go via AT&T,  that was the
easy part...its just no matter how many times I preppend their AS in the
advertisement though me almost every route server shows I'm providing
the most preferred path for some reason...

Thanks,
 
Chad Monteith
Technology Specialists
voice: 260.422.3979
fax: 260.422.5775

-----Original Message-----
From: Ejay Hire [mailto:ejay.hire@isdn.net] 
Sent: Wednesday, June 25, 2003 5:28 PM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] RE: Disapearing prefix problems

Hi.

To load balance this customer, you need to:
- send at&t 7018:20 on your customer route
- have your customer send 7018:20 to at&t for this route
- have your customer as-prepend one time for his route advertisement to
at&t.

That should do it.  If not, then fiddling with localpref communities is
the next step.

-Ejay
-----Original Message-----
From: Chad Monteith [mailto:chadlist@tspec.net]
Sent: Wednesday, June 25, 2003 11:05 AM
To: isp-bgp@isp-bgp.com
Subject: [isp-bgp] Disapearing prefix problems


Hello List, 

I'm scratching my head on this one, hoping someone can help me....

We are providing transit to one of our clients that also has a
connection to AT&T.  They are advertising a single /24 they have
received from AT&T out both their AT&T feed and ours.  

Here's what I'm having trouble with.  When I don't advertise their
connection out my feed I can go to any route server and I see their /24
in the routing table.  Once I start advertising them to my upstreams, I
become the preferred path instead of AT&T in virtually all cases.

The client is sending the 7018:20 community to AT&T, and when I drop my
connection to them I can verify this is working since I do see their /24
instead of just the AT&T aggregate.

I've tried doing as path prepends to get incoming traffic to prefer the
AT&T feed, but no matter how long I make the path most route servers
still show our transit connection as preferred.

It should be noting, that AT&T is also one of our upstreams, along with
two other providers.  I'm wondering if that may have something to do
with it, but I may not be smart enough to figure out how :o)

Any helpful hints would be appreciated.
  


Thanks,
 
Chad Monteith
Technology Specialists
voice: 260.422.3979
fax: 260.422.5775



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