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1. At the console, press Ctrl+^ (Ctrl+Shift-6).
2. Press the X key to terminate the Telnet session.
Pressing Ctrl+^ twice in a row causes a single Ctrl+^ character to be sent to the Telnet server. After
you press Ctrl+^ , pressing any key other than X or Ctrl+^ returns you to the Telnet session.
Network Time Protocol Version 4 (NTPv4)
NTPv4 feature synchronizes the local system clock in the device with the UTC. The synchronization is
achieved by maintaining a loop-free timing topology computed as a shortest-path spanning tree rooted
on the primary server. NTP does not know about local time zones or daylight-saving time. A time server
located anywhere in the world can provide synchronization to a client located anywhere else in the
world. It allows clients to use different time zone and daylight-saving properties. Primary servers are
synchronized by wire or radio to national standards such as GPS. Timing information is conveyed from
primary servers to secondary servers and clients in the network. NTP runs on UDP, which in turn runs
on IP.
NTP has a hierarchical structure. NTP uses the concept of a stratum to describe how many NTP hops
away a machine is from an authoritative time source. A stratum 1 time server typically has an
authoritative time source such as a radio or atomic clock, or a Global Positioning System [GPS] time
source directly attached. A stratum 2 time server receives its time through NTP from a stratum 1 time
server and so on. As the network introduces timing discrepancies, lower stratum devices are a factor
less accurate. A hierarchical structure allows the overhead of providing time to many clients to be
shared among many time servers. Not all clients need to obtain time directly from a stratum 1 reference,
but can use stratum 2 or 3 references.
NTP operates on a client-server basis. The current implementation runs NTP as a secondary server
and/or a NTP Client. As a secondary server, the device operates with one or more upstream servers
and one or more downstream servers or clients. A client device synchronizes to one or more upstream
servers, but does not provide synchronization to dependant clients. Secondary servers at each lower
level are assigned stratum numbers one greater than the preceding level. As stratum number increases,
the accuracy decreases. Stratum one is assigned to Primary servers.
NTP uses the concept of associations to describe communication between two machines running NTP.
NTP associations are statistically configured. On startup or on the arrival of NTP packets, associations
are created. Multiple associations are created by the protocol to communicate with multiple servers.
NTP maintains a set of statistics for each of the server or the client it is associated with. The statistics
represent measurements of the system clock relative to each server clock separately. NTP then
determines the most accurate and reliable candidates to synchronize the system clock. The final clock
offset applied for clock adjustment is a statistical average derived from the set of accurate sources.
When multiple sources of time (hardware clock, manual configuration) are available, NTP is always
considered to be more authoritative. NTP time overrides the time that is set by any other method.
NTPv4 obsoletes NTPv3 (RFC1305) and SNTP (RFC4330). SNTP is a subset of NTPv4. RFC 5905
describes NTPv4.
To keep the time in your network current, it is recommended that each device have its time
synchronized with at least four external NTP servers. External NTP servers should be synchronized
among themselves to maintain time synchronization.
NOTE
Network Time Protocol (NTP) commands must be configured on each individual device.
Network Time Protocol Version 4 (NTPv4)
FastIron Ethernet Switch Administration Guide 35
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