ND Clocks User Manual - Rev 2.0.1 Sep-08
15
Symmetricom
®
, Inc.
The Broadcast/Multicast timeout period (in minutes) is adjustable when this mode is selected.
[Note: While listening to NTP broadcasts, the network clock cannot query the time server.]
[Note: Some NTP/SNTP clients will expect NTP servers to operate on port 123 and cannot be configured to utilize
alternate ports.]
Listen for NTP via Multicast Address
The network clock can be set up to listen to NTP using multicast addressing by selecting the “Listen for NTP via
multic
ast address(es)” checkbox.
When enabled, the multicast class D / group address may be specified as well as the frequency that multicast
bro
adcasts will be issued. This can be changed as desired. The ND clock can listen for NTP multicast broadcasts
using the full class D/ group address range. The ND 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 (224.0.1/24) [ Internetwork Control Block] is
utilized for NTP traffic, however, please refer to the RFC3171 for your specific application and implementation.
[Note: While listening to NTP broadcasts/multicasts, the network clock cannot be configured to query the time
server.]
[Note: Some NTP/SNTP clients will expect NTP servers to operate on port 123 and cannot be configured to utilize
alternate ports.]
The network clock can be configured to either listen to NTP multicast or broadcasts only, or to
query the NTP time server at a selected interval. The default configuration is to query the NTP
server at 10-minute intervals. To configure the ND device to only listen to NTP broadcasts, click
the checkbox for “Listen for NTP broadcasts only”, and enter a “Broadcast timeout” in minutes.
The default timeout is 60 minutes.
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