User manual

Masterclock RC 500 User Manual – v2014.01.01

Listen for NTP via multicast address(s)

The network device can be set up to listen to NTP using multicast addressing by selecting the

“Listen for NTP via multicast address(s)” checkbox.

Select by clicking

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” – “224.0.1.255” (Internetwork Control Block) is used

for NTP traffic; however, please refer to the RFC3171 for your specific application and implementation.

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.