North American Network Operators Group

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Re: How Not to Multihome

  • From: Justin M. Streiner
  • Date: Mon Oct 08 18:36:28 2007

On Mon, 8 Oct 2007, [email protected] 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.