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NTP is Network Time Protocol, as defined in RFC 1305. SNTP is Simple Network Time Protocol, as defined in RFC 2030. These are commonly used to keep computers' clocks in sync.



(S)NTP servers usually run on UDP port 123.

Packet Length

NTP packets are always 48 bytes long.


l7-filter uses the ntp pattern. NTP packets are purely binary data and contain very little identifying information. Therefore, in order for the l7-filter pattern to reliably match NTP, the pattern had to be written in such a way that it sometimes also matches random traffic from other binary protocols. Be cautious when using this pattern.

See also