2nd October 2019


What is on port 123?

NTP is a widely deployed time synchronization service listening on UDP port 123. The attacker spoofs source IPs and sends a small query to a vulnerable NTP server, which generates a large reply of response data to the spoofed addresses.

What is NTP protocol?

Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware.

What is the port for NTP?

OpenNTPD also uses high-numbered source ports so if it is able to synchronize but ntpd is not, it is very probable that the incoming UDP port 123 is blocked. If you're going to run ntpd , you need to fix your network/firewall/NAT so that ntpd can have full unrestricted access to UDP port 123 in both directions.
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