NTP poll-based associations

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 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.