The Network Time Protocol (NTP) is defined in RFC 1305, Network Time Protocol (Version 3) Specification, Implementation and Analysis. It allows participating network nodes to keep time more accurately and maintain time in a more synchronized manner between the participating network nodes.
NTP uses stratum levels to define the number of hops from a reference clock. The reference clock is treated as 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 7210 SAS devices cannot act as stratum-1 servers but can act as stratum-2 devices because a network connection to an NTP server is required.
The higher stratum levels are separated from the stratum-1 server over a network path, therefore 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.
If the internal PTP process is used as a time source for System Time and OAM, it must be specified as a server for NTP. If PTP is specified, the prefer parameter must also be specified. After PTP has established a UTC traceable time from an external grandmaster source, that clock will always be the time source into NTP, even if PTP goes into time holdover.
Use of the internal PTP time source for NTP promotes the internal NTP server to stratum 1 level. This may impact the NTP network topology.
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. By default, the node will, by default, transmits NTP packets in NTP version 4 mode.
authentication keys
These keys implement increased security support in carrier and other networks. Both DES and MD5 authentication are supported, as well as multiple keys.
symmetric active mode
In this mode, the NTP is 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
In this mode, the node receives or sends using a broadcast address.
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, SNTP transitions to an operationally down state. If NTP is removed from the configuration or shut down, SNTP resumes an operationally up state.
gradual clock adjustment
Because several applications (such as Service Assurance Agent (SAA)) can use the clock, if a major adjustment (128 ms or more) is needed, it is performed by programmatically stepping the clock. If a minor (less than 128 ms) adjustment is needed, it is performed by either speeding up or slowing down the clock.
rate limit events and traps
To avoid the generation of excessive events and traps the NTP module rate limits the generation of events and traps to three per second. At that point, a single trap is generated to indicate that event and trap squashing is taking place.