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SNTP Time Synchronization
For synchronizing the system clock with outside time sources, the SR OS includes a Simple
Network Time Protocol (SNTP) client. As defined in RFC 2030, SNTP Version 4 is an adaptation
of the Network Time Protocol (NTP). SNTP typically provides time accuracy within 100
milliseconds of the time source. SNTP can only receive the time from NTP servers; it cannot be
used to provide time services to other systems. SNTP is a compact, client-only version of NTP.
SNTP does not authenticate traffic.
SNTP can be configured in both unicast client modes (point-to-point) and broadcast client modes
(point-to-multipoint). SNTP should be used only at the extremities of the synchronization subnet.
SNTP clients should operate only at the highest stratum (leaves) of the subnet and in
configurations where no NTP or SNTP client is dependent on another SNTP client for
synchronization. SNTP time servers should operate only at the root (stratum 1) of the subnet and
then only in configurations where no other source of synchronization other than a reliable radio
clock is available. External servers may only be specified using IPv4 addresses.
In the SR OS, the SNTP client can be configured for either broadcast or unicast client mode.
7950 SR OS Basic System Configuration Guide
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
performed by either speeding up or slowing down the clock.
In order to facilitate proper operation once the standby CPM takes over from the active
CPM it is required that the time on the secondary is synchronized with the clock of the
active CPMIn order to avoid the generation of too many events/trap the NTP module will
rate limit the generation of events/traps to three per second. At that point a single trap will
be generated that indicates that event/trap squashing is taking place.
System Management
Page 229
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