D: Network Time Protocol (NTP)
Editing MD5 keys on the XL-GPS
NTP keys are needed if you are using NTP in broadcast mode with MD5 authentication. This
(and the following) section provide configuration guidelines. For additional information,
consult Dr. Mills NTP site at: http://www.ntp.org
Broadcast mode adjusts its periodicity according to feedback from its broadcast client. The
periodicity will typically settle-out to about every 2 minutes. This activity is not adjustable.
MD5 private keys have to be edited on both the NTP server and the NTP client. The private
keys are defined in the “ntp.keys” file.
The NTP client “ntp.keys” file is identical to the one on the NTP server. For the
specific keys used by the NTP server, the NTP client must have the identical line in its
version of the file. You’ll want to use your own hard-to-guess key names, using random
letters. The critical lines of the “ntp.keys” file are:
1 M symmetricom
2 M TTXL-GPS
where:
• “1” and “2” are the key identifiers
• “M” specifies MD5 authentication, the only type available
• “symmetricom” and “TTXL-GPS” are the arbitrarily chosen keys
The first column is the key identification number, which may range in whole positive numbers
from 1 to 65,535. The second column is the type of key, which is always set to the letter M
when using MD5 authentication. The third column is the private key that is ASCII text from 1
to 32 characters in length.
Up to eight MD5 can be established.
Editing MD5 keys on the NTP Client
For NTP client authentication, the line trustedkey 1 2 in the “ntp.conf” file is required to
enable the private keys 1 and 2 from the “ntp.keys” file. The line bclient is required for
broadcast time packets to be processed by the NTP client. In this case, sample information
from a client “ntp.conf” file might look like:
trustedkey 1 2
bclient
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