North American Network Operators Group|
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical
Re: Disaster recovery using as-prepend?
On Fri, 17 Feb 2006, Christopher L. Morrow wrote: > > > If your primary is connected to ISP_A and the backup is connected to ISP_B, > > > customers connected to ISP_B MAY still flow to your backup DC (ISP_B will > > > probably set local preference on all customer routes - you should be able to > > > override this behavior with communities but not all providers support this (or > > > honor it 100% of the time!)) > > > > And in addition to that, even multihomed customers of ISP_B may choose the > > prepended route for a number of different reasons; for instance, ISP_B might > > be a cheaper pipe for them, or there may be a smart-ish routing device or > > scheme in play that overrides normal BGP decision making. > > I might be crazy, but couldn't you just prepend the route enough to > effectively poison it at ingress to 'backup-isp' ? Some route decision override schemes don't care what the path length is at all, or factor it in with such a low weight, such that no reasonable amount of prepending will change the situation. With the development of source traffic engineering schemes, prepending is no longer reliable as a means of affecting routing on the remote side. That perception will have to die with it (hopefully sooner rather than later). -- -- Todd Vierling <[email protected]> <[email protected]> <[email protected]>