Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 42)

NTP packets periodically (every 64 sec) to subnet broadcast IP address of the configured interface.
• NTP broadcast packets are sent to the configured subnet when the NTP broadcast server is
configured on the interface which is up and the IP address is configured for the broadcast subnet
under the following conditions:
‐ The local clock is valid and the system clock is synchronized
‐ The local clock is valid and the system clock is not synchronized
‐ Authentication key is configured, the system clock is synchronized and the local clock is
valid
• NTP broadcast packets are not sent in the following cases:
‐ 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
NTP broadcast client
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