[ntp:questions] Best practice: re-resolve server IP address before each poll/query

Richard B. Gilbert rgilbert88 at comcast.net
Tue Jun 12 20:15:11 UTC 2007

Jan Ceuleers wrote:
> All,
> One of my favourite articles on the interweb is the following (about the 
> Netgear/UWisc debacle).
>  http://www.cs.wisc.edu/~plonka/netgear-sntp
> In the list of best practice recommendations it makes about SNTP 
> implementations, it says:
> "SHOULD resolve the server IP address via DNS before each poll/query, so 
> that the pertinent DNS entries' Time-To-Live values are respected."
> I was wondering whether the readership of this forum feels that this 
> should also apply to NTP implementations.
> Cheers, Jan

I'll vote a definite NO!  An SNTP client might query five or six times a 
day!  An NTP client will query as frequently as once per minute and 
doing a DNS lookup each time would border on the absurd. IP addresses do 
not change all that often and a system that did change IP addresses 
frequently would not be much use as an NTP server.

If an IP address stops responding to NTP queries, it would be reasonable 
to query DNS again.  Once!  If you get the same IP address again, the 
server must be presumed down.

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