System Management Parameters
Page 210 7750 SR OS Basic System Configuration Guide
Network Time Protocol (NTP)
NTP is the Network Time Protocol defined in RFC 1305, Network Time Protocol (Version 3)
Specification, Implementation and Analysis. 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 7750
SR-7 and 7750 SR-12 devices cannot act as stratum-1 servers but can act as stratum-2 devices as
a network connection to an NTP server is required.
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.
The following NTP elements are supported:
• Server mode — In this mode, the node advertises the ability to act as a clock source for
other network elements. In this mode, the node will, by default, transmit NTP packets in
NTP version 4 mode.
• Authentication keys — Increased security support in carrier and other network has been
implemented. Both DES and MD5 authentication are supported as well as multiple keys.
• Operation in symmetric active mode — This capability requires that NTP be synchronized
with a specific node that is considered more trustworthy or accurate than other nodes
carrying NTP in the system. This mode requires that a specific peer is set.
• Broadcast or multicast modes — When operating in these modes, the node will receive or
send using either a multicast (default 224.0.1.1) or a broadcast address. Multicast is
supported on the MGMT port.
• Alert when NTP server is not available — When none of the configured servers are
reachable on the node, the system reverts to manual timekeeping and issues a critical
alarm. When a server becomes available, a trap is issued indicating that standard operation
has resumed.
• NTP and SNTP — If both NTP and SNTP are enabled on the node, then SNTP transitions
to an operationally down state. If NTP is removed from the configuration or shut down,
then SNTP resumes an operationally up state.
• Gradual clock adjustment — As several applications (such as Service Assurance Agent
(SAA)) can use the clock, and if determined that a major (128 ms or more) adjustment
needs to be performed, the adjustment is performed by programmatically stepping the
clock. If a minor (less than 128 ms) adjustment must be performed, then the adjustment is
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