RFC 958 - Network Time Protocol (NTP)

Network Time Protocol. Network Time Protocol (NTP) is the default time synchronization protocol used by the Windows Time service in the operating system. NTP is a fault-tolerant, highly scalable time protocol and is the protocol used most often for synchronizing computer clocks by using a designated time reference. Here is a brief list of standard ports and their designations: 21 – FTP; 22 – SSH; 25 – SMTP (sending email) 53 – DNS (domain name service) 80 – HTTP (web server) 110 – POP3 (email inbox) 123 – NTP (Network Time Protocol) 143 – IMAP (email inbox) 443 – HTTPS (secure web server) 465 – SMTPS (send secure email) 631 – CUPS In short, ntp client sends UDP request from random port >1023 to port 123 on ntp server. It waits response on the same originating port. Your firewall should be able to keep open originating port for UDP traffic from ntp server. Nov 05, 2008 · Network Time Protocol (NTP) is widely used in order to synchronize a computer to Internet time servers or other sources, such as a radio or satellite receivers or telephone modem services. It provides accuracies typically less than a millisecond on LANs and up to a few milliseconds on WANs.

Feb 08, 2013 · If I have 20 PC's on a private LAN and they all sync to pool.ntp.org, in your explanation, a client send an NTP query, the firewall NAT's the LAN IP to a public IP and of it goes. Independently, and supposedly oblivious to the request being made, an unknown server on the internet fires an NTP response at the firewall.

NTP runs on UDP port 123. The Windows 2000 version of this service uses Simple Network Time Protocol (SNTP). SNTP also runs on UDP port 123. When the Windows Time service uses a Windows domain configuration, the service requires domain controller location and authentication services. Therefore, the ports for Kerberos and DNS are required. You can also use the continental zones (For example europe, north-america, oceania or asia.pool.ntp.org), and a country zone (like ch.pool.ntp.org in Switzerland) - for all these zones, you can again use the 0, 1 or 2 prefixes, like 0.ch.pool.ntp.org. Note, however, that the country zone might not exist for your country, or might contain only

Multiple NTP ports: Having a time server that supports offers multiple NTP ports accommodates modern networks as well as ones destined to be upgraded at some future point in time. If your network is going to grow, or security is important, you want your time server to keep pace with it.

Sep 30, 2019 · synchronised to NTP server (149.20.54.20) at stratum 3 time correct to within 42 ms polling server every 1024 s Use the echo command to display exit status of ntp client: $ echo $? Sample outputs: 0 Checking the status of NTP with ntpq command. The ntpq utility program is used to monitor NTP daemon ntpd operations and determine performance. Simple Network Time Protocol (SNTP) is an Internet Protocol (IP) used to synchronize the clocks of networks of computers. SNTP is a subset of the Network Time Protocol (NTP). The latest version is SNTP v4. It can synchronize seamlessly to full-blown NTP servers. Originally developed for small computers and micro-controllers. NTP Cheat Sheet NTP Cheat Sheet v1.0 (308 kB) NTP Short Reference (A4, 2 pages), English language. Contains short lists of the most important NTP configuration parameters, command line options and file formats used by NTP, e.g. for the keyfile or the statistic files that can be generated by ntpd (loopstats, peerstats, clockstats, sysstats). These ports are assigned to specific server sevice by the Internet Assigned Numbers Authority (IANA). For example, port 80 is used by web servers. Port 1024 to 49151: These are ports that an organization, such as application developers, can register with IAMA to be used for a particular service. These should be treated as semi-reserved. Your 'when' column is telling me that ntp last chatted with those servers at best 40 minutes ago, yet your poll interval is 1024 seconds (~17 minutes). ntp does not seem to be running properly, which makes sense given your firewall configuration. You'll need an outbound and an inbound allow rule for UDP 123. Aug 16, 2017 · A major part of securing a Linux system is locking down unused ports to stop them from being accessed and ultimately hijacked by attackers. Linux systems are built to be servers, so attackers would attempt to use a compromised system that way, even if that system was set up to be a desktop.