vi /etc/ntp.conf

server 120.119.28.1

server 220.135.58.124

server 129.6.15.28

server 129.6.15.29

# Use Ubuntu's ntp server as a fallback.

#server ntp.ubuntu.com

server 91.189.94.4

#server 91.189.89.199

 

vi /etc/network/iptables.up.rules

-A INPUT -s 129.6.15.0/24 -j ACCEPT -m comment --comment "time.nist.gov"

-A INPUT -s 91.189.94.4 -j ACCEPT -m comment --comment "NTP-ubuntu"

-A INPUT -s 91.189.89.199 -j ACCEPT -m comment --comment "NTP-ubuntu"

-A INPUT -s 202.112.0.0/16 -j ACCEPT -m comment --comment "cn.pool.ntp.org"

-A INPUT -s 120.119.28.1 -j ACCEPT -m comment --comment "tw.pool.ntp.org"

-A INPUT -s 220.135.58.124 -j ACCEPT -m comment --comment "tw.pool.ntp.org"

-A OUTPUT -d 91.189.94.4 -j ACCEPT -m comment --comment "NTP"

-A OUTPUT -d 91.189.89.199 -j ACCEPT -m comment --comment "NTP"

-A OUTPUT -s 202.112.0.0/16 -j ACCEPT -m comment --comment "cn.pool.ntp.org"

-A OUTPUT -s 120.119.28.1 -j ACCEPT -m comment --comment "tw.pool.ntp.org"

-A OUTPUT -s 220.135.58.124 -j ACCEPT -m comment --comment "tw.pool.ntp.org"