Port 1433: MSSQL
Port 1433 is the default listener for Microsoft SQL Server. Like all database ports, it should be reachable only from application servers, never from the open internet.
| Port number | 1433 |
|---|---|
| Service | Microsoft SQL Server |
| Protocol | TCP |
| Category | Databases |
| Default encryption | No |
How do I check whether port 1433 is open?
Port 1433 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 1433 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 1433 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':1433 ' | Lists the process bound to port 1433 on Linux. On macOS use lsof -nP -iTCP:1433 -sTCP:LISTEN, on Windows netstat -ano | findstr :1433 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 1433 used for?
Port 1433 is the default listener for Microsoft SQL Server. Like all database ports, it should be reachable only from application servers, never from the open internet.
Is port 1433 TCP or UDP?
Port 1433 (MSSQL) uses TCP.
Is port 1433 secure?
Port 1433 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 1433 on my firewall?
Only if you specifically need MSSQL. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.