Ntp Broadcast Mode Without Authentication; Configuration Of Ntp On The Timeserver - Symmetricom Time Server User Manual

Appendix B: MD5 Authentication and NTP Broadcast Mode
B.3

NTP Broadcast Mode without Authentication

Authentication was configured off by default for NTP version 3, but is configured on by
default for version 4. This means that NTP version 4 must use authentication, like MD5,
for broadcast time to work. To have it otherwise, you must specifically turn
authentication off in the "ntp.conf" file of the NTP time client.
The method outlined below should only be used when the LAN that the two NTP hosts are on is
a secure network. Otherwise, it is all too easy for an NTP time imposter to broadcast the
incorrect time to the NTP time client.
B.3.1

Configuration of NTP on the Timeserver

For the NTP timeserver, authentication may be on or off - it does not matter. As an
example, here is a sample "ntp.conf" file.
server
server
server
broadcast
This file is stored on the Symmetricom timeserver in its Flash disk drive in the "/etc"
directory.
The critical line is:
• This line turns on the periodic broadcast of NTP time packets to the local LAN.
This IP address (the first three octets: 192.168.1) is a network address.
The LAN portion of the address, the last octet in this case, is set to all ones. You
may use all zeros for most LANs as the LAN address, instead of all ones. This
address allows NTP time packets to be received by all hosts on the local LAN
including the NTP time client. Ask your system administrator what your LAN
broadcast address is for your particular network and substitute it for the address in
this example.
B-102
192.168.1.49
206.54.0.20
206.54.0.21
192.168.1.255
broadcast 192.168.1.255.
TimeVault™ User's Manual
NTP Broadcast Mode without Authentication
6000-100AppB.fm Rev. D