| SNTP, Simple Network Time Protocol |
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Description | Glossary | RFCs | Publications | Obsolete RFCs |
| Protocol suite: | TCP/IP. |
| Protocol type: | Application layer time protocol. |
| Base protocol: | NTP, Network Time Protocol. |
| Port: | 123 (UDP). |
| MIME subtype: | |
| SNMP MIBs: | |
| Working groups: | |
| Links: |
| MAC header | IP header | UDP header | SNTP message |
SNTP message, version 4:
| 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LI | VN | Mode | Stratum | Poll | Precision | ||||||||||||||||||||||||||
| Root Delay | |||||||||||||||||||||||||||||||
| Root Dispersion | |||||||||||||||||||||||||||||||
| Reference Identifier | |||||||||||||||||||||||||||||||
| Reference Timestamp - | |||||||||||||||||||||||||||||||
| Originate Timestamp - | |||||||||||||||||||||||||||||||
| Receive Timestamp - | |||||||||||||||||||||||||||||||
| Transmit Timestamp - | |||||||||||||||||||||||||||||||
| Key Identifier | |||||||||||||||||||||||||||||||
| Message Digest - - - | |||||||||||||||||||||||||||||||
LI, Leap Indicator.
2 bits.
This code warns of an impending leap second to be inserted/deleted in the last minute of the current day.
| LI | Description |
|---|---|
| 0 | No warning. |
| 1 | Last minute has 61 seconds. |
| 2 | Last minute has 59 seconds. |
| 3 | Alarm condition (clock not synchronized). |
VN, Version Number.
3 bits.
The NTP/SNTP version number.
If necessary to distinguish between IPv4, IPv6 and OSI, the encapsulating context must be inspected.
| VN | Description |
|---|---|
| 0 | |
| 1 | |
| 2 | |
| 3 | IPv4 only. |
| 4 | IPv4, IPv6 and OSI. |
| 5 | |
| 6 | |
| 7 |
Mode. 3 bits.
| Mode | Description |
|---|---|
| 0 | Reserved. |
| 1 | Symmetric active. |
| 2 | Symmetric passive. |
| 3 | Client. |
| 4 | Server. |
| 5 | Broadcast. |
| 6 | Reserved for NTP control message. |
| 7 | Reserved for private use. |
Stratum.
8 bits.
Stratum level of the local clock.
| Stratum | Description |
|---|---|
| 0 | Unspecified or unavailable. |
| 1 | Primary reference (e.g., radio clock). |
| 2 - 15 |
Secondary reference (via NTP or SNTP). |
| 16 - 255 |
reserved. |
Poll.
8 bits, signed.
The maximum interval between successive messages, in seconds to the nearest power of two.
The values that can appear in this field presently range from 4
(16 s) to 14 (16284 s); however, most applications use only the sub-range 6 (64 s) to 10 (1024 s).
Precision.
8 bits.
The precision of the local clock, in seconds to the nearest power of two.
The values that normally appear in this field range from -6 for mains-frequency
clocks to -20 for microsecond clocks found in some workstations.
Root Delay.
32 bits, signed fixed point.
The total roundtrip delay to the primary reference source, in seconds with
fraction point between bits 15 and 16. Note that this variable can take on both
positive and negative values, depending on the relative time and frequency
offsets. The values that normally appear in this field range from negative
values of a few milliseconds to positive values of several hundred milliseconds.
Root Dispersion.
32 bits, unsigned fixed point.
The nominal error relative to the primary reference source, in seconds with
fraction point between bits 15 and 16. The values that normally appear in this
field range from 0 to several hundred milliseconds.
Reference Identifier.
32 bits.
The reference source.
In the case of NTP Version 3 or Version 4 stratum-0
(unspecified) or stratum-1 (primary) servers, this is a four-character ASCII
string, left justified and zero padded to 32 bits. In NTP Version 3 secondary
servers, this is the 32-bit IPv4 address of the reference source. In NTP Version
4 secondary servers, this is the low order 32 bits of the latest transmit
timestamp of the reference source. NTP primary (stratum 1) servers should set
this field to a code identifying the external reference source according to the following list.
If the external reference is one of those listed, the associated code should be used.
Codes for sources not listed can be contrived as appropriate.
| Code | Description |
|---|---|
| ACTS | NIST dialup modem service. |
| CHU | Ottawa (Canada) Radio 3330, 7335, 14670 kHz. |
| DCF | Mainflingen (Germany) Radio 77.5 kHz. |
| GOES | Geostationary Orbit Environment Satellite. |
| GPS | Global Positioning Service. |
| LOCL | Uncalibrated local clock used as a primary reference for a subnet without external means of synchronization. |
| LORC | LORAN-C radionavigation system. |
| MSF | Rugby (UK) Radio 60 kHz. |
| OMEG | OMEGA radionavigation system. |
| PPS | Atomic clock or other pulse-per-second source individually calibrated to national standards. |
| PTB | PTB (Germany) modem service. |
| TDF | Allouis (France) Radio 164 kHz. |
| USNO | USNO modem service. |
| WWV | Ft. Collins (US) Radio 2.5, 5, 10, 15, 20 MHz. |
| WWVB | Boulder (US) Radio 60 kHz. |
| WWVH | Kaui Hawaii (US) Radio 2.5, 5, 10, 15 MHz. |
Reference Timestamp. 64 bits.
The time at which the local clock was last set or corrected.
Originate Timestamp. 64 bits.
The time at which the request departed the client for the server.
Receive Timestamp. 64 bits.
The time at which the request arrived at the server.
Transmit Timestamp. 64 bits.
The time at which the reply departed the server for the client.
Key Identifier. 32 bits.
Optional.
Message Digest.
128 bits.
Optional.
RFCs:
[RFC 4330] Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI.
[RFC 1361] Simple Network Time Protocol (SNTP).
[RFC 1769] Simple Network Time Protocol (SNTP).
[RFC 2030] Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI.
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Description | Glossary | RFCs | Publications | Obsolete RFCs |