Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 43)

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
mode is a peer-to-peer relationship, the host will also retain time-related information of the local
networking device that it is communicating with. When many mutually redundant servers are
interconnected via diverse network paths, the symmetric active mode should be used. Most stratum 1
and stratum 2 servers on the Internet adopt the symmetric active form of network setup. The FastIron
device operates in symmetric active mode, when the peer information is configured using the peer
command and specifying the address of the peer. The peer is also configured in symmetric active
mode in this way by specifying the FastIron device information. If the peer is not specifically
configured, a symmetric passive association is activated upon arrival of a symmetric active message.
The specific mode that you should set for each of your networking devices depends primarily on the
role that you want them to assume as a timekeeping device (server or client) and the device's
proximity to a stratum 1 timekeeping server. A networking device engages in polling when it is
operating as a client or a host in the client mode or when it is acting as a peer in the symmetric active
mode. An exceedingly large number of ongoing and simultaneous polls on a system can seriously
impact the performance of a system or slow the performance of a given network. To avoid having an
excessive number of ongoing polls on a network, you should limit the number of direct, peer-to-peer
or client-to-server associations. Instead, you should consider using NTP broadcasts to propagate
time information within a localized network.
NTP broadcast-based associations
The broadcast-based NTP associations should be used in configurations involving potentially large
client population. Broadcast-based NTP associations are also recommended for use on networks that
have limited bandwidth, system memory, or CPU resources.
The devices operating in the broadcast server mode broadcasts the NTP packets periodically which can
be picked up by the devices operating in broadcast client mode. The broadcast server is configured
using the broadcast command.
A networking device operating in the broadcast client mode does not engage in any polling. Instead, the
device receives the NTP broadcast server packets from the NTP broadcast servers in the same subnet.
The NTP broadcast client forms a temporary client association with the NTP broadcast server. A
broadcast client is configured using the broadcast client command. For broadcast client mode to work,
the broadcast server and the clients must be located on the same subnet.
NTP broadcast-based associations
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