NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38. See ConfiguringModemRefclocksDev for discussion of this topic.
ntp-4.2.8p15 was released on 23 June 2020. It addresses 1 medium-severity security issue in ntpd, and provides 13 non-security bugfixes over 4.2.8p13.
Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.
6.1.10. Configuring Modem Refclocks
Dave Mills uses:
server 127.127.18.1 minpoll 12 maxpoll 17
phone atdt913034944774 atdt917195676742
This calls NIST in Boulder CO first, and if that fails USNO in Boulder is called.
The initial '9' is to obtain an outside line.
Dave also says: The phone string is copied verbatim to the modem as per Hayes command
set. You can test by sending the same string to the modem using a terminal
program. You can also test using the NTP filegen facility and flag 4 set on
the fudge command. The modem protocol and command responses are written to
the clockstats file.
Dave found the following:
I stumbled on
Apparently, PTB does something similar to NIST.
It can measure and correct for the propagation delay.
However, while the NIST correction is automatic, the PTB correction
must be enabled by a special sequence, as quoted below.
The communication parameters are: CCITT-V.22 modem, 1200 baud, 8 ASCII data
bits, one stop bit, no parity. The change from CR (carriage return) to LF
(line feed) indicates the beginning of each transmitted second. The
information transmitted before this time marker (leading edge of the start
bit of the LF) refers to the next
In order to correct for the propagation delay time, the code transmission is
stopped by the command "//" (two slashes), the incoming CR-LF time markers
are echoed back, and the time code generator is set by the command "GDM" (do
generator delay time measurements) into the GDM mode. In this mode, the time
code generator measures 8 round-loop delays, calculates the mean value and
the standard deviation and advances the time marker for half the mean value
determined. If the GDM has been successful, the visible time marker will
change from "*" to "#".
The result of the delay time determination is reported in the time protocols
Related Topics: ModemRefclockUsers