User manual

Masterclock NTDS-A User Manual – Original – 2013-04-25
17
LISTEN FOR NTP VIA MULTICAST
The network clock can be set up to listen to NTP using
multicast addressing by selecting the “Listen for NTP via
multicast address(s)” checkbox.
When enabled, the “Multicast class D / Group address”
may be specified as well as the frequency that multicast
broadcasts will be issued. This can be changed as desired.
The network clock can listen for NTP multicast broadcasts
using the full class D/ group address range. The network
clock does not restrict the use of the multicast address
assignment and supports the full range of class D multicast
addresses or groups from “224.0.0.0” to “239.255.255.255”.
These groups (or class D address ranges for multicasting) are
defined and governed by RFC3171, IANA IPv4 Multicast
Guidelines.
Typically, the multicast address range “224.0.1.0 to
224.0.1.255” (Internetwork Control Block) is used for NTP
traffic. However, please refer to the RFC3171 for your
specific application and implementation.
Listen/Query Restrictions
while listening to NTP broadcasts/
multicasts, the network clock cannot be
configured to query the time server.
Some NTP/SNTP clients will expect NTP
servers to operate on port 123 and
cannot be configured to use alternate
ports.
The static IP address you enter must not
be in use by another device on the
network, this includes IP address ranges
reserved for use by the DHCP server. If a
static IP address is used which creates a
duplicate IP address condition, the
network clock will be assigned a fallback
IP address of “169.254.xxx.xxx”.
The “169.254.xxx.xxx” address is a link
local address range (i.e. not allowed on
the internet) and is used by Microsoft
when their DHCP clients cannot find a
DHCP server.