[dns-operations] TCP anycast was Re: DNS query logging

Francis Dupont Francis.Dupont at fdupont.fr
Fri Mar 18 23:33:58 UTC 2011

 In your previous mail you wrote:

   Perhaps.  But then again maybe not.  TCP is a relation between two 
   end points, in between it is IP.  If the path changes out below a TCP 
   session and the routing converges before a timeout happens, TCP 
   wouldn't care.  However, it's been decades before I had deep enough 
   knowledge to give any specifics.
   With UDP, any sneeze may lose the packet.  But even if it whirlpools 
   a bit before getting home, so long as it's in the time window, it's 
=> in fact you missed another case: I saw only once anycast leading
to a broken service:
 - a load-balancer was in front of a pool of (two) servers
 - the load-balancer became a bit bad and duplicated packets,
  i.e., sent incoming packets to both servers in place of selecting
  on at the first packet of a flow and keeping it
 - TCP queries failed in a strange way getting both answers and TCP
 - the load-balancer was rebooted
and the service has been worked pretty well since many years...


Francis.Dupont at fdupont.fr

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