Open port checker

The port is closed although forwarding is set up

• Your ISP may use CGNAT: the router’s WAN address is in 100.64.0.0/10 or differs from what My IP shows. Incoming connections then need a public IP from the ISP.
• The service is not running, or listens on 127.0.0.1 only.
• The Windows firewall or a router rule (on MikroTik, the forward chain) drops the packets.
• The ISP blocks the port, most often 25, 135–139 and 445.

TCP only

This checks TCP. A UDP port cannot be reliably checked from outside: a closed UDP port and one that simply did not reply look the same. For SIP servers, use the SIP check.