NTP

Installation:

$ apt-get install ntp

By default NTP listens on all interfaces:

$ netstat -uan | grep ntp
udp        0      0 10.10.10.254:ntp        *:*                                
udp        0      0 server.example.com:ntp  *:*                                
udp        0      0 localhost:ntp           *:*                                
udp        0      0 *:ntp                   *:*                                
udp6       0      0 fe80::216:3eff:fe00:ntp [::]:*                             
udp6       0      0 fe80::216:3eff:fe00:ntp [::]:*                             
udp6       0      0 fe80::4c53:aaff:feb:ntp [::]:*                             
udp6       0      0 fe80::3cbb:efff:fe9:ntp [::]:*                             
udp6       0      0 localhost:ntp           [::]:*                             
udp6       0      0 [::]:ntp                [::]:*

To cleanup that list add a interface directive to /etc/ntp.conf:

interface listen eth0

And restart NTP:

$ /etc/init.d/net restart

After the change the list should look like this:

$ netstat -uan | grep ntp
udp        0      0 server.example.com:ntp  *:*                                
udp        0      0 localhost:ntp           *:*                                
udp        0      0 *:ntp                   *:*                                
udp6       0      0 fe80::216:3eff:fe00:ntp [::]:*                             
udp6       0      0 localhost:ntp           [::]:*                             
udp6       0      0 [::]:ntp                [::]:*