User manual

Masterclock www.masterclock.com
15
MULTICAST
The network device also supports Multicast
Addressing of NTP packets. Multicasting is useful
because it conserves bandwidth. Multicasting’s
replicate only the necessary packets and only as
needed to send them only to clients that want them.
The concept of a group, and group membership, is
crucial to multicasting. Every multicast requires a
multicast group; the sender transmits to the group
address, and only members of the group can receive
the multicast data. A group is defined by a Class D
address.
The network device 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 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.
The IGMP (Internet Group Management Protocol)
controls group membership for individual hosts. This
protocol only operates in a LAN setting, but is
required if you wish to be able to join a multicast
group on a host. IGMP is defined in RFC 2236.
ANYCAST
The network device does not currently provide
Anycast capability.
STATIC IP
To use a static IP address, de-select the checkbox for
“Automatically obtain network configuration from
DHCP/BOOTP.” You must enter the IP address,
netmask, gateway, primary DNS and also a secondary
DNS.
Devices which have been assigned a fallback IP
address of “169.254.xxx.xxx” will be displayed in the
main WinDiscovery window with RED text, indicating
a problem with the configuration.
NTP CLIENT AUTHENTICATION SETTINGS
The CLDNTD12 series uses the MD5 Message Digest
Algorithm, which is a widely used cryptographic hash
function that produces a 128-bit hash value.
IGMP
Use of the multicast addressing method
requires the use of routers and switches and
other network devices which support the
Internet Group Management Protocol (IGMP).
In addition, the IGMP mode must be enabled
and configured for multicast addressing to be
implemented properly. Please ensure that
your network system components are capable
of, and configured properly for, IGMP before
utilizing the multicast addressing feature.
Consult you network administrator for
assistance in utilizing the multicast addressing
feature.
FIREWALLS
Check with your firewall vendor to determine
how to enable multicast traffic through a
firewall. In addition, you may want to read
RFC 2588: IP Multicast and Firewalls.
Port 123
Some NTP/SNTP servers will expect NTP
clients to operate on port 123.
If the advanced settings have been altered for
your clock and you begin experiencing
difficulty in getting your clock to synchronize
to the NTP time server, or the clock begins
acting erratically, try returning the advanced
settings to the default values: “123.”
NTP CLIENT ADVANCED SETTINGS
From the NTP Client window, the [NTP Client
Advanced Settings] button allows for the
adjustment of additional network
communication settings. Under most
operating circumstances it is not necessary
to change these settings.
The factory-default TCP/UDP port for NTP
service is: “123”