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ntp: use NTP instead of echo for presend

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Switch to NTP for presend as the echo service (RFC 862) is rarely
enabled. When presend is active, send an NTP client packet to the
server/peer and ignore the reply.

This also fixes presend with separate client sockets. The destination
port can't be changed on connected sockets, so the echo packet was sent
to the NTP port instead of the echo port.
This commit is contained in:
Miroslav Lichvar
2014-08-15 15:45:48 +02:00
parent ff4abc69c3
commit cd5105b1db
4 changed files with 18 additions and 32 deletions
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12
chrony.texi.in
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@@ -2836,18 +2836,18 @@ of the machines.
In order to avoid this problem, the @code{presend} option may be used.
It takes a single integer argument, which is the smallest polling
interval for which a pair of packets will be exchanged between the
client and the server prior to the actual measurement being initiated by
the client. For example, with the following option included in a
interval for which an extra pair of NTP packets will be exchanged
between the client and the server prior to the actual measurement.
For example, with the following option included in a
@code{server} directive :
@example
presend 9
@end example
when the polling interval is 512 seconds or more, a UDP echo datagram
will be sent to the server a short time (currently 4 seconds) before the
NTP client mode datagram.
when the polling interval is 512 seconds or more, an extra NTP client
packet will be sent to the server a short time (currently 4 seconds)
before making the actual measurement.
@item key
The NTP protocol supports the inclusion of checksums in the packets, to