‐
NTP broadcast server is configured on the interface which is down even if the system clock
is synchronized and the local clock is valid.
‐
NTP broadcast server is configured on the interface which is up and no IP address is
configured for the broadcast subnet even if the system clock is synchronized and the local
clock is valid.
‐
NTP broadcast server is configured on the interface which is not present and no IP address
is configured for the broadcast subnet even if the system clock is synchronized and the local
clock is valid.
‐
NTP broadcast server without authentication key is configured on the interface which is up
and the IP address is configured for the broadcast subnet even when NTP authentication is
enforced and the system clock is synchronized and the local clock is valid.
NTP broadcast client
An NTP broadcast client listens for NTP packets on a broadcast address. When the first packet is
received, the client attempts to quantify the delay to the server, to better quantify the correct time from
later broadcasts. This is accomplished by a series of brief interchanges where the client and server act
as a regular (non-broadcast) NTP client and server. Once interchanges occur, the client has an idea of
the network delay and thereafter can estimate the time based only on broadcast packets.
NTP associations
Networking devices running NTP can be configured to operate in variety of association modes when
synchronizing time with reference time sources. A networking device can obtain time information on a
network in two ways-by polling host servers and by listening to NTP broadcasts. That is, there are two
types of associations-poll-based and broadcast-based.
NTP poll-based associations
The following modes are the NTP polling based associations:
1. Server mode
2. Client mode
3. Symmetric Active/Passive
The server mode requires no prior client configuration. The server responds to client mode NTP
packets. Use the master command to set the device to operate in server mode when it has lost the
synchronization.
When the system is operating in the client mode, it polls all configured NTP servers and peers. The
device selects a host from all the polled NTP servers to synchronize with. Because the relationship
that is established in this case is a client-host relationship, the host will not capture or use any time
information sent by the local client device. This mode is most suited for file-server and workstation
clients that are not required to provide any form of time synchronization to other local clients. Use the
server and peer to individually specify the time server that you want the networking device to
consider synchronizing with and to set your networking device to operate in the client mode.
Symmetric active/passive mode is intended for configurations where group devices operate as
mutual backups for each other. Each device operates with one or more primary reference sources,
such as a radio clock, or a subset of reliable NTP secondary servers. If one of the devices lose all
reference sources or simply cease operation, the other peers automatically reconfigures. This helps
the flow of time value from the surviving peers to all the others.
When a networking device is operating in the symmetric active mode, it polls its assigned time-
serving hosts for the current time and it responds to polls by its hosts. Because symmetric active
NTP broadcast client
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