Port 3128 (Squid proxy)

Default port of the Squid HTTP proxy; also used by many other forward proxies.

Registered (user) port, 1024-49151 TCP Proxies and Tor Do not expose to the internet

What port 3128 is used for

Default port of the Squid HTTP proxy; also used by many other forward proxies.

Security: should port 3128 be open?

Do not expose to the internet. An open proxy is abused for spam, fraud and attacks that appear to come from your IP. Allow only your own clients (http_access) and require auth if remote.

IANA assignment

Service nameProtoDescriptionAssigneeReference

ndl-aas TCP Active API Server Port Martin Norman -

ndl-aas UDP Active API Server Port Martin Norman -

Check what is listening on port 3128

Linux: is anything listening on TCP 3128?

sudo ss -tlnp 'sport = :3128'

Linux / macOS: which process owns the port

sudo lsof -nP -i :3128

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':3128 '

Windows (Command Prompt)

netstat -ano | findstr :3128

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3128 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 3128

From Windows

Test-NetConnection HOST -Port 3128

Block port 3128 in the firewall

ufw

sudo ufw deny 3128/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 3128 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 3128 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 3128' -Direction Inbound -Protocol TCP -LocalPort 3128 -Action Block

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.