gerexperience.blogg.se - What is wireshark time in

These variables are seen on the wire for NTP packets. The key ID is the number of the key while the MAC is the message digest (currently MD5 or SHA-1, not to be confused with the Ethernet MAC address). key ID & MAC: Only present when you’re using NTP authentication.If you roughly want to know the time by looking at an NTP packet, look at this transmit timestamp. transmit timestamp: “Time at the server when the response left for the client.” This is the most interesting timestamp in those NTP packets since it shows the time the NTP client/server had as it sent the NTP packet.

( Since I am merely using IPv6 for this NTP blog post series you’ll always see these curious-looking “refid” values in the ntpq output. Above stratum 1 this is either the IPv4 address of the reference NTP server or for IPv6 “it is the first four octets of the MD5 hash of the IPv6 address.” <- D’oh! This looks quite strange.

reference ID: “32-bit code identifying the particular server or reference clock.” For stratum 1 servers this is an ASCII string telling you the reference clock such as GPS, PPS or DCFa/DCFp.

Supported are values up to 15, while 16 means unsynchronized. ) You won’t see values greater than 4 on the Internet that often. An NTP server that receives its time from a stratum 1 server increases the value by 1, that is: 2. That is: When a server replies with stratum 1, it is directly connected to a reference clock. While the reference clock (if one is used) internally has a stratum value of 0, the NTP server that syncs to that clock has a stratum value of 1.

stratum: The stratum value gives the distance to the reference clock.

Other modes are “symmetric active” (2) between NTP peers and “NTP control message” (6) for controlling/polling NTP servers.

This is the basic client-server unicast request which you’ll see all over your network. mode: The most common modes are client (3) and server (4).version: “3-bit integer representing the NTP version number, currently 4.”.leap indicator: “2-bit integer warning of an impending leap second to be inserted or deleted in the last minute of the current month.Note that I am NOT explaining the NTP algorithm at all, but only the packets and their fields that are present on the network. Looking on the wire you should understand the packet header ( section 7.3 in the RFC). Have a look at the current NTPv “Network Time Protocol Version 4: Protocol and Algorithms Specification” in order to understand the packets and protocol details.