Port 3128: Squid
Port 3128 is the traditional default port for the Squid caching proxy, widely used to filter, cache, and log outbound web traffic for a network. It is a long-standing convention rather than an IANA assignment.
| Port number | 3128 |
|---|---|
| Service | Squid caching proxy |
| Protocol | TCP |
| Category | Proxy & tunneling |
| Default encryption | No |
How do I check whether port 3128 is open?
Port 3128 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 3128 | 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 3128 | 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 ':3128 ' | Lists the process bound to port 3128 on Linux. On macOS use lsof -nP -iTCP:3128 -sTCP:LISTEN, on Windows netstat -ano | findstr :3128 |
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 3128 used for?
Port 3128 is the traditional default port for the Squid caching proxy, widely used to filter, cache, and log outbound web traffic for a network. It is a long-standing convention rather than an IANA assignment.
Is port 3128 TCP or UDP?
Port 3128 (Squid) uses TCP.
Is port 3128 secure?
Port 3128 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 3128 on my firewall?
Only if you specifically need Squid. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.