Technical data

FastIron Ethernet Switch Administration Guide 25

53-1002637-02

Network Time Protocol Version 4 (NTPv4)

NOTE

Use the master command with caution. It is very easy to override valid time sources using this

command, especially if a low stratum number is configured. Configuring multiple machines in the

same network with the master command can cause instability in timekeeping if the machines do not

agree on the time.

NTP Client

An NTP client gets time responses from an NTP server or servers, and uses the information to

calibrate its clock. This consists of the client determining how far its clock is off and adjusting its

time to match that of the server. The maximum error is determined based on the round-trip time for

the packet to be received.

The NTP client can be enabled when we enter the ntp command and configure one or more NTP

servers/peers.

The NTP client maintains the server and peer state information as association. The server and peer

association is mobilized at the startup or whenever user configures. The statically configured

server/peer associations are not demobilized unless user removes the configuration. The

symmetric passive association is mobilized upon arrival of NTP packet from peer which is not

statically configured. The associations will be demobilized on error or time-out.

NTP peer

NTP peer mode is intended for configurations where a group of devices operate as mutual backups

for each other. If one of the devices loses a reference source, the time values can flow from the

surviving peers to all the others. Each device operates with one or more primary reference sources,

such as a radio clock, or a subset of reliable NTP secondary servers. When one of the devices lose

all reference sources or simply cease operation, the other peers automatically reconfigures so that

time values can flow from the surviving peers to others.

When the NTP server or peer is configured with burst mode, client will send burst of up to 8 NTP

packets in each polling interval. The burst number of packets in each interval increases as the

polling interval increases from minimum polling interval towards maximum interval.

The NTP peer can operate in:

• Symmetric Active-When the peer is configured using the peer command.

• Symmetric Passive-Dynamically learned upon arrival of a NTP packet from the peer which is

not configured. The symmetric passive association is removed on timeout or error.

The following scenarios are observed when the upstream server is not reachable after retries:

• If the NTP server/peer is configured and the master command is not configured, then the

system clock is synchronized. When the system clock is synchronized, the server will respond

to client's request with the stratum number set to +1. And when the system clock is

unsynchronized, the server will respond to client's request with the stratum number set to 16.

• If the NTP server/peer is configured and the master command is configured, then the system

clock is synchronized. When the system clock is synchronized, the reference time is the local

clock time. If the local clock is valid then the server will respond to client's request with the

specified stratum number if it is configured otherwise with the default stratum number.