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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
View file

@ -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

18
ntp_core.c
View file

@ -85,8 +85,8 @@ struct NCR_Instance_Record {
received packets) */
int presend_minpoll; /* If the current polling interval is
at least this, an echo datagram
will be send some time before every
at least this, an extra client packet
will be send some time before normal
transmit. This ensures that both
us and the server/peer have an ARP
entry for each other ready, which
@ -191,7 +191,7 @@ struct NCR_Instance_Record {
#define IBURST_GOOD_SAMPLES 4
#define IBURST_TOTAL_SAMPLES SOURCE_REACH_BITS
/* Time to wait after sending echo to 'warm up' link */
/* Time to wait after sending packet to 'warm up' link */
#define WARM_UP_DELAY 4.0
/* The NTP protocol version that we support */
@ -820,7 +820,7 @@ transmit_timeout(void *arg)
}
/* Check whether we need to 'warm up' the link to the other end by
sending an echo exchange to ensure both ends' ARP caches are
sending an NTP exchange to ensure both ends' ARP caches are
primed. On loaded systems this might also help ensure that bits
of the program are paged in properly before we start. */
@ -828,8 +828,11 @@ transmit_timeout(void *arg)
(inst->presend_minpoll <= inst->local_poll) &&
!inst->presend_done) {
/* Send */
NIO_SendEcho(&inst->remote_addr, &inst->local_addr);
/* Send a client packet, don't store the local tx values
as the reply will be ignored */
transmit_packet(MODE_CLIENT, inst->local_poll, NTP_VERSION, 0, 0,
&inst->remote_orig, &inst->local_rx, NULL, NULL,
&inst->remote_addr, &inst->local_addr);
inst->presend_done = 1;
@ -1483,6 +1486,9 @@ NCR_ProcessKnown
break;
case MODE_SERVER:
/* Ignore presend reply */
if (inst->presend_done)
break;
switch(inst->mode) {
case MODE_ACTIVE:

17
ntp_io.c
View file

@ -687,20 +687,3 @@ NIO_SendAuthenticatedPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
{
send_packet((void *) packet, NTP_NORMAL_PACKET_SIZE + auth_len, remote_addr, local_addr);
}
/* ================================================== */
/* We ought to use getservbyname, but I can't really see this changing */
#define ECHO_PORT 7
void
NIO_SendEcho(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr)
{
unsigned long magic_message = 0xbe7ab1e7UL;
NTP_Remote_Address addr;
addr = *remote_addr;
addr.port = ECHO_PORT;
send_packet((void *) &magic_message, sizeof(unsigned long), &addr, local_addr);
}

3
ntp_io.h
View file

@ -56,7 +56,4 @@ extern void NIO_SendNormalPacket(NTP_Packet *packet, NTP_Remote_Address *remote_
/* Function to transmit an authenticated packet */
extern void NIO_SendAuthenticatedPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr, int auth_len);
/* Function to send a datagram to a remote machine's UDP echo port. */
extern void NIO_SendEcho(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr);
#endif /* GOT_NTP_IO_H */