into my linux server (Ubuntu 8) I have top open the port 123 for ntp. I have write this into /etc/iptables.rules::INPUT ACCEPT [7496:9080183] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [4393:322232] [0:0] -A INPUT -p udp -m udp --sport 8100 -j ACCEPT [0:0] -A INPUT -p udp -m udp --dport 8100 -j ACCEPT [0:0] -I INPUT -p udp --dport 123 -j ACCEPT [0:0] -I OUTPUT -p udp --sport 123 -j ACCEPT COMMIT
Sep 14, 2009 · As you may know there are currently two ways of performing a time sync between the local computer and remote time servers: 1.) over UDP port 123 (SNTP) =to prefer UDP Port 123 may use a defined protocol to communicate depending on the application. A protocol is a set of formalized rules that explains how data is communicated over a network. Think of it as the language spoken between computers to help them communicate more efficiently. Aug 27, 2019 · TCP/UDP: Remote Procedure Call (RPC) 1057, 1831: sunrpc: Portmap (sunrpc) 113: TCP: Identification Protocol: 1413: ident — 119: TCP: Network News Transfer Protocol (NNTP) 3977: nntp: Apps that read newsgroups. 123: UDP: Network Time Protocol (NTP) 1305: ntp: Date & Time preferences, network time server synchronization, Apple TV network time udp 53, udp 123, udp 514, udp 1194,udp 3386, udp 3480, udp 10000-30000, tcp 110, tcp 53 and tcp 443. This port information can be useful if you have a special network configuration with a firewall device upstream of the Ooma Hub or Telo Base Station that restricts application ports on the inside or “private side” of your network for : 20 Implementations send and receive timestamps using the User Datagram Protocol (UDP) on port number 123.   They can also use broadcasting or multicasting , where clients passively listen to time updates after an initial round-trip calibrating exchange. 
Re: Opening UDP port 123 Thanks for the info. At this point, I don't think it's a problem with the firewall blocking any ports, as this hasn't been a problem in the past and at some point the time does get corrected.
This is because all NTP servers need access to User Datagram Protocol (UDP) port 123, and as long as the Windows Time service is running on the Windows Server 2003 operating system, port 123 remains reserved by Windows Time. Network Ports Used by Windows Time Service Sep 09, 2015 · In Windows Server 2008 R2 environment, inbound UDP communication may be blocked when the connection to the network is interrupted and then restored. Inbound TCP and ICMP communications may also be blocked in this situation. This problem occurs if the inbound UDP communication is enabled by Windows Firewall. Jul 21, 2016 · Hi. We test the connection with tcp port using the command: telnet IpAdress tcpPort. for instance: telnet 10.10.1.20 8080. but, how can I do to test the connection with an udp port.
Jul 20, 2020 · Service Name and Transport Protocol Port Number Registry Last Updated 2020-07-20 Expert(s) TCP/UDP: Joe Touch; Eliot Lear, Allison Mankin, Markku Kojo, Kumiko Ono, Martin Stiemerling, Lars Eggert, Alexey Melnikov, Wes Eddy, Alexander Zimmermann, Brian Trammell, and Jana Iyengar SCTP: Allison Mankin and Michael Tuexen DCCP: Eddie Kohler and Yoshifumi Nishida
123. NTP UDP Network Time Protocol. 137-139. NetBIOS TCP and UDP TCP/IP legacy support for the outdated NetBOIS protocol. 143. IMAP TCP Internet Message Access