[99914] in North American Network Operators' Group
Re: How Not to Multihome
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Mon Oct 8 21:27:26 2007
In-Reply-To: <Pine.LNX.4.64.0710081816240.4258@whammy.cluebyfour.org>
Cc: "Patrick W. Gilmore" <patrick@ianai.net>
From: "Patrick W. Gilmore" <patrick@ianai.net>
Date: Mon, 8 Oct 2007 21:23:27 -0400
To: nanog <nanog@merit.edu>
Errors-To: owner-nanog@merit.edu
On Oct 8, 2007, at 6:19 PM, Justin M. Streiner wrote:
> On Mon, 8 Oct 2007, Keegan.Holley@sungard.com wrote:
>
>> That brings up an interesing point. My biggest fear was that one
>> of my
>> other customers could possible be closer to me that the ISP that
>> provides
>> the primary link and it would cause them to favor the backup link
>> because
>> of AS path. I think they are going to fight me on this and
>> telling them
>> to multihome to their original ISP would probably be frowned upon
>> at this
>> point. I was hoping that there was an RFC for multihoming that I
>> could
>> use to bail myself out.
>
> If you went ahead and did this, the more specific route being
> announced by you on behalf of your customer would be more likely to
> attract traffic back to you. Prefix length is checked in the BGP
> route selection process before AS path length. This would work in
> normal "everything works fine" situations, but when things break,
> troubleshooting the source of the customer's reachabilit woes will
> get very interesting.
You have made an assumption that the original upstream would not
originate a prefix equivalent to the one you are originating.
--
TTFN,
patrick
