NTP - Config
configured, the two nodes can synchronize with each other in a variety of failure
scenarios, such as loss of GPS and Internet connectivity. See system peer mode:
symmetric-active under NTP Daemon Status (on page 28).
n Typical Usage: The user configures NTP associations on two NTP nodes that
point to the each other. The two nodes are usually of equal stratum and have inde-
pendent references, such as two separate GPS installations or two separate net-
work paths to NTP servers on the Internet. In the event of a reference failure, the
peers can synchronize to the node that has the best remaining reference.
n
Broadcast:
n Addressing: Use an IPv4 broadcast address of the local subnet. To broadcast
NTP messages on a subnet, if the local interface IP address were 192.168.61.58
and the mask were 255.255.255.0, the broadcast address could be
192.168.61.255.
n Description: Creates a broadcast server association. When configured with a
broadcast address (e.g., 192.168.61.255), the association broadcasts NTP mes-
sages from the network interface with the matching IP address (e.g.,
192.168.61.58). Broadcast messages go out to all nodes on the subnet, and are
usually blocked by routers from reaching adjacent subnets. Consult with the net-
work administrator to select a correctly-scoped address and Time to live value.
n This type of association requires authentication on both the server and the clients.
See Using NTP Authentication (on page 160).
n Typical Usage: Broadcast associations to reduce network traffic with a large num-
ber of NTP clients.
n Broadcast Client:
n Addressing: The user does not specify an address with this setting.
n Description: Creates an association that listens for NTP broadcast messages on
all of the network interfaces. Upon receiving the first broadcast message, the
broadcast client association initiates a brief exchange with the server to calibrate
the propagation delay. Afterwards, the broadcast client association listens to and
gets the time from the broadcast server messages. This type of association
requires authentication on both the server and the clients. See Using NTP
Authentication (on page 160).
n Typical Usage: Broadcast client associations can get authenticated time on net-
works that have a broadcast server.
n Multicast Server: Create a Broadcast association with members of a multicast group.
The multicast address is a class D address starting from 224.0.0.1. (The IANA assigned
224.0.1.1 to be the NTP multicast address.) However, user can choose any class D
address that is not used on the local network by other protocols. Routers can be con-
figured to transmit multicast messages to adjacent subnets.
n
Multicast Client:
n Addressing: Use the same IPv4 class D multicast address as the Multicast Server
(potentially 224.0.1.1).
n Description: Creates an association that listens for NTP multicast messages on all
of the network interfaces. Upon receiving the first message, the multicast client
997-01520-02 Rev. F1.......................................................................... Page 45
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