Information About Network Time Protocol
Network Time Protocol (NTP) synchronizes timekeeping among a set of distributed time servers and clients. With this synchronization, you can correlate events to the time that system logs were created and the time that other time-specific events occur. An NTP server must be accessible by the client switch.
An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock that is attached to a time server. NTP distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of one another.
NTP uses a stratum to describe how many NTP hops away a machine is from an authoritative time source. A stratum 1 time server has a radio or atomic clock that is directly attached, a stratum 2 time server receives its time from a stratum 1 time server, and so on. A machine running NTP automatically chooses as its time source the machine with the lowest stratum number that it is configured to communicate with through NTP. This strategy effectively builds a self-organizing tree of NTP speakers.
NTP has two ways to avoid synchronizing to a machine whose time might be ambiguous:
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NTP never synchronizes to a machine that is not synchronized itself.
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NTP compares the time that is reported by several machines and does not synchronize to a machine whose time is significantly different from the others, even if its stratum is lower.
The communications between machines running NTP, known as associations, are usually statically configured; each machine is given the IP addresses of all machines with which it should form associations. An associated pair of machines can keep accurate timekeeping by exchanging NTP messages between each other. However, in a LAN environment, you can configure NTP to use IP broadcast messages. With this alternative, you can configure the machine to send or receive broadcast messages, but the accuracy of timekeeping is marginally reduced because the information flow is one-way only.
NTP Work Mode
NTP supports 4 working modes for clock synchronization:
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Client Mode:
In this mode, the OLT device or client sends regularly time-of day requests to a configured NTP server
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Peer Mode:
In this mode, an NTP-configured device establishes an association with another peer device and synchronizes the time with each other.
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Broadcast Mode:
In this mode, the NTP server sends the time information to all connected clients in the same subnet as the server.
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Multicast Mode:
In this mode, the NTP server and clients have multicast configured and the NTP server sends the time information to only multcast-configured clients