Re: How Not to Multihome

["Patrick W. Gilmore" <patrick () ianai net>]

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