Is my port open?
Check from 28 locations.
Test if a specific TCP or UDP port is open and accepting connections from 28 servers across 16 countries.
Test if a specific TCP or UDP port is open and reachable from 28 worldwide locations.
Note: All checks are public. To keep your checks private, create a free account.
Global Network Diagnostics
Run a check to see your service from around the world.
- Tested from 28 monitoring locations worldwide
- Results in seconds, not minutes
- Shareable result links for your team
- No account or signup required
What is a Port Check?
Every network service runs on a numbered port — a logical endpoint that allows your operating system to route incoming connections to the correct application. Web servers listen on port 80 (HTTP) and 443 (HTTPS), SSH daemons on port 22, and databases on their own dedicated ports. When you run a port check, you test whether that endpoint is reachable from the outside world.
TCP vs UDP
TCP (Transmission Control Protocol) is connection-oriented. To check a TCP port, a tool initiates a three-way handshake (SYN → SYN-ACK → ACK). If the remote server completes the handshake, the port is open. If it sends back a RST (reset) packet, the port is closed. If there is no response at all, the port is likely filtered — blocked by a firewall before the packet ever reaches the service.
UDP (User Datagram Protocol) is connectionless and harder to test definitively. A UDP port check sends a datagram and waits for a response or an ICMP "port unreachable" message. Silence can mean the port is open and the service is running, or it may mean a firewall is silently dropping packets.
Port States Explained
- Open — A service is actively listening on this port and accepted the connection. Your application is reachable.
- Closed — The host responded but no service is listening. The port is accessible but not in use.
- Filtered — A firewall, security group, or ACL is blocking the connection. No response was received within the timeout window.
Common Reasons to Check a Port
- Verify a newly deployed service is accessible after configuring firewall rules
- Troubleshoot why users cannot connect to a database or API endpoint
- Confirm a VPN or hosting provider is not blocking specific ports
- Test whether a service is reachable globally or only from certain regions
- Validate that a security configuration correctly blocks unauthorized ports
How it works
- Enter a hostname or IP address and port number
- Select TCP or UDP protocol
- Our 28 monitoring nodes each attempt a connection
- Results show open, closed, or filtered status per location
Need advanced diagnostics?
The full Emercom Tools application includes traceroute, MTR with ASN lookup, and port connectivity tests with detailed timing information.
Open Emercom ToolsCommon Ports Reference
Use this table as a quick reference when checking the most frequently used TCP and UDP ports for common services.
| Port | Service | Protocol | Description |
|---|---|---|---|
| 21 | FTP | TCP | File Transfer Protocol — control channel for file transfers |
| 22 | SSH | TCP | Secure Shell — encrypted remote login and command execution |
| 25 | SMTP | TCP | Email sending — server-to-server mail transfer |
| 53 | DNS | TCP/UDP | Domain Name System — hostname to IP address resolution |
| 80 | HTTP | TCP | Web traffic — unencrypted hypertext transfer |
| 443 | HTTPS | TCP | Secure web traffic — TLS-encrypted hypertext transfer |
| 3306 | MySQL | TCP | MySQL database server connections |
| 5432 | PostgreSQL | TCP | PostgreSQL database server connections |
| 6379 | Redis | TCP | Redis in-memory data store and cache |
| 8080 | HTTP Alt | TCP | Alternative HTTP port — common for dev servers and proxies |
| 8443 | HTTPS Alt | TCP | Alternative HTTPS port — common for application servers |
| 27017 | MongoDB | TCP | MongoDB document database server connections |
Why Check Ports From Multiple Locations?
A port that appears open from your office may be completely unreachable to users in other regions. Testing from a single location gives you an incomplete picture.
Geo-Blocking
Some organizations and cloud providers apply geo-based firewall rules that block traffic from specific countries or regions. A port may be accessible from the US but blocked from Asia or Europe.
ISP-Level Port Blocking
Internet service providers in certain countries block specific ports by default — port 25 (SMTP) is commonly blocked by residential ISPs worldwide to prevent spam. Testing from multiple ISPs surfaces these restrictions.
Asymmetric Firewall Rules
Firewall rules often allow connections from known office or VPN IP ranges while blocking everything else. What works from your laptop may be silently dropped for external users and customers.
CDN and Load Balancer Routing
CDN edge nodes and anycast load balancers route traffic differently depending on the source region. A port may be open on some edge nodes but misconfigured or unavailable on others, causing intermittent failures for users in specific locations.
Related Tools
Port availability is just one piece of network diagnostics. Use these complementary tools for a complete picture.
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