Re: Geographic routing hack

["Alec H. Peterson" <ahp () hilander com>]

Martin Cooper wrote:
> Some weeks ago I noticed that 167.216.128.247/32
> (www.digisle.net) appears to reach web servers
> located in physically different places broadly
> dependent on where you see it from.
>
> I presume this is done by advertising the same
> prefix from border routers which are in seperate
> IGP domains or something (confederations maybe?),
> but I wonder what people's views on the concept are,
> since it could potentially be quite confusing in
> certain circumstances (e.g. debugging routing
> problems) ?
>
> Superficially it seems like a 'cool hack' for
> geographic content-distribution (which is what
> Digital Island do), but up until now I've always
> seen this sort of thing done by exploiting NS
> record sorting order properties with the kludge
> of different A records in the various zonefiles,
> and I wondered if doing it with routing policy in
> this way is strictly RFC compliant (or for that
> matter if anyone cares if it isn't) ?

This certainly isn't a new idea, although it is generally considered poor
form to do this with stateful protocols (such as TCP), since the 'closest'
instance of the address can change mid-session, and thus cause a reset.

Several presentations on using this hack in various situations have been
made at NANOG.  See http://www.hilander.com/nanog11 for one such
presentation.

Alec

-- 
Alec H. Peterson - ahp () hilander com
Staff Scientist
CenterGate Research Group - http://www.centergate.com
"Technology so advanced, even _we_ don't understand it!"