System Management
Basic System Configuration Guide 239
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.
CRON
The CRON feature supports periodic and date and time-based scheduling in SR OS. CRON
can be used, for example, to schedule Service Assurance Agent (SAA) functions. CRON
functionality includes the ability to specify scripts that need to be run, when they will be
scheduled, including one-time only functionality (one-shot), interval and calendar functions.
Scheduled reboots, peer turn ups, service assurance agent tests and more can all be scheduled
with CRON, as well as OAM events, such as connectivity checks, or troubleshooting runs.
CRON supports the schedule element. The schedule function configures the type of schedule
to run, including one-time only (one-shot), periodic, or calendar-based runs. All runs are
determined by month, day of month or weekday, hour, minute, and interval (seconds).
High Availability
This section discusses the high availability (HA) routing options and features available to
service providers that help diminish vulnerability at the network or service provider edge and
alleviate the effect of a lengthy outage on IP networks.
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