IPBulucu.orgNetwork & DNS Tools
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TCP Reachability Test

Open Port Checker & Port Forwarding Test

Check TCP reachability from the IPBulucu server for web, mail and administrative ports you are authorized to test.

Timeouts are inconclusive. This does not test UDP, identify the listening service or establish that a host is secure.

What are you checking?

For a NAS, camera or another application, find its configured TCP port. If the router translates external to internal ports, test the external port here.

Selecting a preset only fills the port. A test starts when you press Check Port.

For a remote server, enter its address instead. Your current connection may use a VPN or a different exit.

Port references: Minecraft · Microsoft RDS

Compare router WAN and public IPv4

Copy the WAN IPv4 from your router's Internet status page, then the public IPv4 from an IP lookup on the same connection. The LAN gateway (often 192.168.1.1) is not the WAN address.

Comparison runs in this tab. Entered addresses are not sent by this tool or saved. It cannot confirm CGNAT.

Find my public IPCheck a TCP port

Address ranges: RFC 6598 · RFC 1918

Port forwarding not working? Follow these checks

Work through the steps and retest only the relevant port after each change.

  1. 1. Check the local service

    Confirm that the application is running and listening on the intended TCP port. Try it from another device on your LAN. Service names beside port numbers are conventional labels.

  2. 2. Compare WAN and public IPv4 addresses

    Check the router WAN page. 100.64.0.0/10 is shared address space. A mismatch can indicate NAT or a different exit path; ask your provider to confirm CGNAT.

    Check your public IP →

  3. 3. Review forwarding and firewall rules

    The rule must point to the correct local device and TCP port. Its address may have changed. Allow only the required service instead of disabling the entire firewall.

  4. 4. Check the domain's destination

    Review A and AAAA records. DNS changes and different IPv4/IPv6 destinations can affect results. A timeout alone does not prove that a port is closed.

    Look up DNS records →

References · IETF · TCP (RFC 9293) · IETF · Shared address space (RFC 6598)

FAQ

Frequently Asked Questions

Questions about network tools and interpreting results.

A port scanner attempts to establish TCP socket handshakes with specific port numbers on a server or IP address to determine if associated services (HTTP, HTTPS, SSH, FTP, MySQL) are publicly reachable.