SNTP in a Local Area Network - General Practices

Resolving The Problem

Network Time Protocol (NTP) is used by business and governments alike to keep time stamps created by operating systems and applications in sync with each other. Computer clocks are not very accurate and can lose time in a relatively short period of time.

In the corporate environment, many clients requesting the current time on UDP port 123 can choke off Internet bandwidth. Therefore most firewalls and, in some cases, switches are configured to drop this traffic.

The accepted implementation is to configure one or two machines on the corporate network to obtain a current time from the National Institute of Standards and Technology (NIST) time servers. The Web site for the NIST servers is
http://tf.nist.gov/tf-cgi/servers.cgi#.

Another option is to configure your switches to be both NTP Clients and Servers. The clients on the local network point to the switch for a time. This saves on network bandwidth because all local requests for time are handled by the local switch, and the switch makes one request of your time server. The switch can also be the server to get a time from the Internet. The concern with this option is whether you want your switch to be accessing a time server outside the internal network. Cisco switches with an operating system version 9.21 or above support an NTP server/client configuration.

References:

For additional information, refer to the following Web sites:

http://support.ntp.org/bin/view/Main/WebHome
www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a008…