Installing and Administering Internet Services

Chapter 7 309

Conﬁguring the Network Time Protocol (NTP)

Advanced NTP Topics

The ﬁrst entry causes packets from source addresses on net 193.100 to be

ignored. However, packets from host 193.100.10.8 are unrestricted, as

speciﬁed by the second entry. The two restriction list entries effectively

cause all packets from net 193.100 to be ignored, with the exception of

packets from host 193.100.10.8.

The following are examples of restriction list entries for a local host with

the address 193.100.100.7. These entries assume that ntpq requests to

the local host can be made only from the local host or the host with

address 193.8.10.1, while the local host only synchronizes to a time

source on net 193.100.

#default entry - matches *all* source addresses

restrict default notrust nomodify

#trust for time, but do not allow ntpq requests

restrict 193.100.0.0 mask 255.255.0.0 nomodify noquery

#ignore time requests, but allow ntpq requests

restrict 193.8.10.1 noserve

#local host address is unrestricted

restrict 193.100.100.7

Starting and Stopping xntpd

To start xntpd, do one of the following:

• Set the environment variable XNTPD to 1 in the ﬁle

/etc/rc.config.d/netdaemons. This causes xntpd to start

automatically whenever the system is booted.

• Issue the following command to run the xntpd startup script:

/sbin/init.d/xntpd start

Command line arguments for starting xntpd may be speciﬁed with the

XNTPD_ARGS environment variable in the ﬁle

/etc/rc.config.d/netdaemons. See the xntpd man page for more

information about command line arguments.

NOTE xntpd should be operated on a continuous basis. If it is necessary to stop

xntpd, the interval when it is not running should be kept to a minimum.