[ntp:questions] NTP client basic
mills at udel.edu
mills at udel.edu
Tue Mar 6 15:33:21 UTC 2007
Hal,
In the far distant past, the most likely source of retransmissions was
link-level retransmissions. In any case, the NTP on-wire protocol
discards duplicates and bogus packets anyway. It does no good whatsoever
to retransmit unanswered packets. If necessary, transmit a new packet
with current timestamps.
Dave
Hal Murray wrote:
>>When the repeats still appeared in my own SNTP client implementation (now
>>trapped, but logged), it seemed to me that I might have stumbled on a
>>possible source of trouble. RFC2030 didn't seem to say that you MUST take
>>steps to discard repeats which COULD arise in the underlying UDP protocol,
>>it seemed to be saying that you could keep an eye on the xmit timestamp in
>>the request - but it's not essential. RFC768 (which describes UDP) doesn't
>>shed any light on whether a corrupted UDP packet could be repeated.
>
>
> It's possible but very very unlikely for the network to duplicate
> a packet.
>
> Is your code retransmitting if you don't get an answer? If so, a
> likely explanation is that you aren't waiting long enough. In
> any case, your code should filter out duplicates and/or process
> them correctly.
>
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