Port 9091: Transmission
Port 9091 is the default web interface port for the Transmission BitTorrent client, letting you add and manage torrents from a browser. It is a convention set by the Transmission project rather than an IANA assignment.
| Port number | 9091 |
|---|---|
| Service | Transmission BitTorrent client web UI |
| Protocol | TCP |
| Category | File transfer |
| Default encryption | No |
How do I check whether port 9091 is open?
Port 9091 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 9091 | 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 9091 | 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 ':9091 ' | Lists the process bound to port 9091 on Linux. On macOS use lsof -nP -iTCP:9091 -sTCP:LISTEN, on Windows netstat -ano | findstr :9091 |
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 9091 used for?
Port 9091 is the default web interface port for the Transmission BitTorrent client, letting you add and manage torrents from a browser. It is a convention set by the Transmission project rather than an IANA assignment.
Is port 9091 TCP or UDP?
Port 9091 (Transmission) uses TCP.
Is port 9091 secure?
Port 9091 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 9091 on my firewall?
Only if you specifically need Transmission. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.