Date: Thu, 11 Dec 1997 11:07:27 -0500 From: Chris Peltier <CPELTIER@iectech.com> To: "'Scot Elliott'" <scot@duff-beer.com> Cc: "'freebsd-isp@freebsd.org'" <freebsd-isp@freebsd.org> Subject: RE: Routing to multihomed hosts Message-ID: <97Dec11.065614est.6196@netgate.iectech.com>
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Scott Elliott wrote: > >I've just set a new server up at our ISP - on three backbones to cope >with >network outages. The A record for the host has all three IP >addresses... >so that presumably any client will choose one at random and then try >the >others if the connect fails. > >This is all very well - but it also means that the client may not be >taking the most direct route to our host. Is there any way to make the >client try the shortest route first.. and is this even desirable? I >seems >to be something that should happen for efficiency's sake but I have no >clue if it's possible. My concern is that on one occasion a client >will >see a fast throughput because the closest address was chosen - but on >another will see poor response because his resolver chose another >address >that got routed via Outer Mongolia or somewhere equally far away. You need to maintain BGP peering sessions with routers on each of these three gateways. This way an Autonomous System (AS) Path is built and clients (hopefully if local preferences anywhere along the way don't interfere) will follow the shortest, available path to you. If you have multiple paths to the same ISP or AS then things get trickier requiring the use of their IGP metrics (MEDS) to select the best outgoing path. On FreeBSD the Gated 3.5.7 Port provides BGP routing functions. Also see the Merit Gated Page at http://www.gated.org . Gated 3.5.8 just came out a couple of days ago.... If you don't want to do this you could have each ISP or AS build and advertise static routes for you for each network block that you use within your network. This will work the same way as above unless one of your links go down. Then all traffic with this short AS will be blackholed and connectivity for some clients will be lost. Sincerely, Chris Peltier * email: CPELTIER@IECTECH.COM * voice: 215-257-4917 * FAX: 215-257-4916 >
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