How Not to Multihome

Mon Oct 8 22:19:54 UTC 2007

On Mon, 8 Oct 2007, Keegan.Holley at 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.

jms