Open port check
Checks the common ports on your own IP address and tells you which are open from the outside. It deliberately runs only against your own address and cannot be pointed at another server.
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What the open port check measures
The open port check tries to connect from the outside to 22 commonly used ports on your own IP address and tells you which are open. The ports are 21, 22, 25, 53, 80, 110, 143, 443, 445, 587, 993, 995, 1194, 1723, 3306, 3389, 5432, 6379, 8080, 8443, 8291 and 27017: file transfer, SSH, mail, DNS, web, Windows file sharing, VPN, databases, remote desktop and MikroTik's management port. Each attempt is given 2.5 seconds, six at a time, from the IPVIEW origin nearest you.
It runs only against the address your visit arrived from and cannot be pointed at another server; leave the box empty and the page checks you. That is a deliberate limit: answering is my port open from outside without turning this server into a scanner. For a single port on another host there is Check one port, which is logged for exactly that reason.
How to read the result
Each port is open, closed or filtered. Open: the connection was made and something is listening, reachable from the whole internet. Closed: the far end refused, which proves the packet arrived at your address and nothing listens there. Filtered: no connection and no refusal, usually because nothing came back within 2.5 seconds and a firewall dropped the packet; it measures the path, not the port.
Nothing open is not the same fact as nothing answering, and the banner keeps them apart. All 22 closed means your address was reached and is shut. All 22 filtered means the packets were dropped before they reached your machine, the normal result from an Iranian mobile carrier or any connection behind the carrier's NAT, where one public address is shared by many subscribers; nothing about your machine was established.
When it is useful
You have set up port forwarding on a router or opened a port in a server's firewall and want to know whether it is really reachable from outside before telling anyone to connect. An open 22 or 3389 that you did not intend is the other finding worth running this for.
Before exposing a database or a management interface, to confirm 3306, 5432, 6379, 27017 and 8291 are not already open to the world. If the port you care about is not among the 22, Check one port tests any port on any host; WHOIS and Reverse DNS answer the other questions about an address.
Common questions
Why can I only check my own IP address?
Because a tool that scanned other people's servers on request would be a scanner, and this site does not run one. The address checked is the one your visit arrived from. Check one port tests a single port on another host and is logged.
What does filtered mean?
No reply within 2.5 seconds: neither a connection nor a refusal. A firewall or a carrier's NAT dropped the packet before it reached you. When every port is filtered, nothing about your ports has been established.
Why does the check say nothing is open when I forwarded the port?
If the port shows closed, the forward is not reaching a listening service; check it is running and bound to the right interface. If it shows filtered, you are most likely behind a carrier-grade NAT, where inbound connections never reach your router; ask your provider for a public address.
Limits. The DNS, WHOIS and SSL tools allow up to 20 requests a minute per IP address. Ping, traceroute and MTR send real packets to their target, so they allow 6 a minute.
The port check runs only against your own IP address. That is deliberate: the question people actually have, "is this port reachable from outside?", is answered by it, while this server cannot be used to scan anyone else's network.
Private and reserved addresses. These are refused by the tools that really connect to their target: the SSL check, ping, traceroute, MTR and the port check. The DNS tools have no such limit, because they only ask a nameserver a question and never connect to the address itself.