System Management
Basic System Configuration Guide 237
Network Time Protocol (NTP)
NTP is the Network Time Protocol defined in RFC 1305, Network Time Protocol (Version 3)
Specification, Implementation and Analysis and RFC 5905, Network Time Protocol Version
4: Protocol and Algorithms Specification. It allows for the participating network nodes to
keep time more accurately and more importantly they can maintain time in a more
synchronized fashion between all participating network nodes.
NTP uses stratum levels to define the number of hops from a reference clock. The reference
clock is considered to be a stratum-0 device that is assumed to be accurate with little or no
delay. Stratum-0 servers cannot be used in a network. However, they can be directly
connected to devices that operate as stratum-1 servers. A stratum-1 server is an NTP server
with a directly-connected device that provides Coordinated Universal Time (UTC), such as a
GPS or atomic clock.
The higher stratum levels are separated from the stratum-1 server over a network path, thus,
a stratum-2 server receives its time over a network link from a stratum-1 server. A stratum-3
server receives its time over a network link from a stratum-2 server.
SR OS routers will normally operate as a stratum 2 or higher device. The router relies on an
external stratum 1 server to source accurate time into the network. However, the SR OS also
allows for the use of the local PTP recovered time to be a source into NTP. In this latter case,
the local PTP source appears as a stratum 0 server and the SR OS advertises itself as a stratum
1 server. Activation of the PTP source into NTP may impact the network NTP topology.
PT Pacific Time Either as PST or PDT, depending
on place and time of year
HST Hawaiian Standard Time UTC -10
AKST Alaska Standard Time UTC -9
AKDT Alaska Standard Daylight Saving
Time
UTC -8
Australia
AWST Western Standard Time (e.g., Perth) UTC +8
ACST Central Standard Time (e.g., Darwin) UTC +9.5
AEST Eastern Standard/Summer Time (e.g.,
Canberra)
UTC +10
Table 29: System-defined Time Zones (Continued)
Acronym Time Zone Name UTC Offset
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