What is port 123?

Port 123 is a well-known port used by NTP over UDP. Network Time Protocol - clock synchronization. A port is like an apartment number at an IP address: it tells incoming traffic which service on the device it belongs to. See the full common ports reference for how this fits with other services.

How to forward port 123

  1. Give the device running NTP a fixed local IP (a static IP or a DHCP reservation) so its address never changes.
  2. Open your router's admin page and find Port Forwarding.
  3. Create a rule forwarding UDP port 123 to that device's local IP.
  4. Save, then test from outside your network.

Walk through it in full with how to set up port forwarding, and plan a stable address with the DHCP pool planner.

Is opening port 123 safe?

Forwarding any port exposes a service to the internet, so only open port 123 if you need it, point it at a single device, and keep that device updated. Read is port forwarding safe? before you open anything.