Port 1434: MSSQL Browser
Port 1434 is the SQL Server Browser service, which listens for UDP requests and reports back which dynamic TCP port a named SQL Server instance is actually using. It exists because named instances do not use the fixed port 1433.
| Port number | 1434 |
|---|---|
| Service | Microsoft SQL Server Browser service |
| Protocol | UDP |
| Category | Databases |
| Default encryption | No |
How do I check whether port 1434 is open?
Port 1434 is UDP, which changes the answer: there is no handshake to complete, so nothing outside the host can prove the port is open. Asking the host itself is the reliable route.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | sudo nmap -sU -p 1434 example.com | UDP has no handshake, so there is nothing to complete. nmap infers the state from whether an ICMP port-unreachable comes back, needs root, and is slow and easy to misread. A silent port may be open, filtered, or simply not replying to a probe it does not recognise. |
| What is listening locally? | ss -ulnp | grep ':1434 ' | Shows the UDP socket bound to port 1434. This is the reliable way to answer the question, because you are asking the host itself rather than guessing from outside. |
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 1434 used for?
Port 1434 is the SQL Server Browser service, which listens for UDP requests and reports back which dynamic TCP port a named SQL Server instance is actually using. It exists because named instances do not use the fixed port 1433.
Is port 1434 TCP or UDP?
Port 1434 (MSSQL Browser) uses UDP.
Is port 1434 secure?
Port 1434 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 1434 on my firewall?
Only if you specifically need MSSQL Browser. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.