The installation of the NTP server on centos 5.6 requires time synchronization between some services and multiple machines in the experiment. Therefore, the prerequisites for building NTP are as follows: 1. install the ntp service yum install ntp. I *-y2, modify/etc/ntp. confrestrict default kod nomodify notrap nopeer noquery # restrict-6 default kod nomodify notrap nopeer noquery # for ipv6 # This is the default ntp setting www.2cto.com # Allow all local operations restrict 127.0.0.1 restrict-6 :: 1 # allowed LAN segments restrict 10.0.0.0 mask 255.0.0.0 nomodify motraprestrict 192.168.0.0 mask 255.255.0.0 nomodify Motrap # use the upper-layer internet ntp server restrict authorization mask authorization limit 255 nomodify notrap noqueryserver limit # If the communication fails with the upper-layer ntp server, the local time is used as the standard time. server 127.127.1.0 stratum 10 # Calculation the frequency error between the ntp server and the upper ntpserver: driftfile/var/lib/ntp/drift # Key file containing the keys and key identifiers used when operating # with Your Ric key cryptography. keys/etc/ntp/keys # logs File logfile/var/log/ntp. log # Description: restrict <IP address> <subnet mask> | <network segment> <subnet mask> [ignore | noquery | notrap | nomodiy | notrust | nokod] ignore: disable all ntp services www.2cto.com noquery: No ntp service notrap: No trap remote event logon function nomodiy: indicates that the client cannot change the time parameter of the ntp server, however, you can use the ntp server to correct the time. notrust: reject the unauthenticated client nokod: kod technology can organize a dos attack 2, modify the/etc/ntp/step-tickers file 207.46.232.182127.127.1.0 # When the ntp server is started, it automatically verifies the time with the recorded ip address in this file. 3, modify/etc/sysconfig/ntpdSYNC_HWCLOCK = YES # Allow B Time synchronization between IOS and System 4 and client configuration is omitted.