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

Rick Jones rick.jones2 at hp.com
Thu Mar 17 17:49:22 UTC 2011

On Thu, 2011-03-17 at 14:06 +0000, Dobbins, Roland wrote:
> On Mar 17, 2011, at 8:32 PM, Edward Lewis wrote:
> > Just want to know how TCP query works in anycast dns server. Will be there any drawback using TCP in anycast
> As you already surmise, same as with UDP.
> There's this myth that anycast isn't suitable for TCP-based
>  applications because of the stateful nature of TCP connections.  But
>  the truth of the matter is that if routing is unstable enough to
>  seriously disrupt sessions to any given anycast node, there are much
>  larger fish to fry on the network(s) in question.
> > We haven't experienced any negative issues relating anycast over TCP.  As in, we have it set up, don't do anything special about it, and it isn't mentioned in system status (ticket) meetings.
> Your experience is representative of other real-world TCP-based anycast
>  deployments, It Just Works.  Nothing broken, so nothing to fix - don't
>  listen to the naysayers, they don't have the production experience you
>  do.

So, what is the frequency of "shifts" for anycast anyway?  The NTP folks
(as expressed in posts to comp.protocols.time.ntp) seem to not be
terribly fond of it even for UDP-based time synchronization.  Those
folks are generally pretty detail-oriented so I'd not necessarily
suspect they would be easily given to fear uncertainty and doubt, but
cannot rule it out entirely.

rick jones

it is merely coincidental anecdote - the NTP daemon on my workstation at
work routinely "discards" time from the internal, anycasted NTP service
in favor of servers that are even of higher stratum.  Could be for any
number of reasons I suppose besides anycast (perhaps OS choice on the
servers) but it does also show the highest jitter of the five servers I
have configured to poll for time.
> ;>
> -----------------------------------------------------------------------
> Roland Dobbins <rdobbins at arbor.net> // <http://www.arbornetworks.com>
> 		The basis of optimism is sheer terror.
> 			  -- Oscar Wilde
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