Subnet and PortsPort 1433: SQL Server
The default port of Microsoft SQL Server.
Registry entry
| Port | Protocols | Registered name | IANA description | Assignee | Reference | Note |
|---|---|---|---|---|---|---|
| 1433 | tcp, udp | ms-sql-s | Microsoft-SQL-Server | n/a | n/a |
What it is used for
The default port of Microsoft SQL Server.
The risk
Exposed instances are attacked with password guessing.
What to do
Firewall it; allow only application servers; use strong accounts.
In the registry
Port 1433 is a user port (1024 to 49151), a range where applications register their own numbers. The registry lists one service for this number. Its main entry is ms-sql-s, "Microsoft-SQL-Server", registered for tcp, udp.
How to find out whether it is open on your computer
On your own computer or server, ask the operating system which programs are listening for connections, and look for port 1433 in the list. If a program you do not recognise listens on it, find out what it is before you close it. From outside, test only networks that you own or have permission to test: scanning other people's networks can be treated as an attack.
Is port 1433 safe to leave open?
It depends on what is listening and who can reach it. Open only what you need, restrict by address where possible, keep the software updated, and use encryption and strong authentication. The advice above applies to this port.
Does the registered name prove what runs on port 1433?
No. Programs can use any port. The registry tells you what the number was reserved for.
This is an independent guide. It is not connected with IANA, the IETF or any network equipment maker. Address and port data come from the IANA registries as fetched on 14 November 2026; RFC texts were read from rfc-editor.org. Check the originals for anything you rely on.