On Sun, Jul 07, 2002 at 08:37:55PM -0400, Stephen Griffin wrote:
In the referenced message, Rodney Joffe said:
Just as a guess, Marshall is probably thinking of using anycast for something other than DNS, like http, or ftp, or telnet. And he's wondering about state ;-)
If you don't use per-packet type load-sharing, but something like per-flow, or per-src/dst-hash, then you can use anycast for protocols which require state (including tcp or other connection-oriented protocols, for that matter).
Worst-case when the server you are communicating with fails, the connection is broken, much as it would had anycast not been in use.
I think the problem they are refering to is what happens if your routing topology changes (or worse, flaps). A stateful connection (like TCP) which would have stayed up during a routing change could potentially be shifted to a different server which obviously wouldn't know the other one's state. Perhaps not terrible for a web server and for recovering from a network outage, but I'd imagine it would be pretty annoying if you managed to develop a persistant oscillation. That is why people use anycast DNS to refer the requester to the closest server with via regular IP, based on which server the request hits. Of course then there is no failover, but thats life. DNS is also more scalable for doing anycast with customers. Which method to use is up to you. :) -- Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/ras PGP Key ID: 0x138EA177 (67 29 D7 BC E8 18 3E DA B2 46 B3 D8 14 36 FE B6)