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Port 3129 (netport-id)

IANA assigns port 3129 to netport-id: NetPort Discovery Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
netport-id TCP NetPort Discovery Port P T K Farrar -
netport-id UDP NetPort Discovery Port P T K Farrar -

Check what is listening on port 3129

Linux: is anything listening on TCP 3129?
sudo ss -tlnp 'sport = :3129'
Linux: UDP 3129
sudo ss -ulnp 'sport = :3129'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3129
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3129 '
Windows (Command Prompt)
netstat -ano | findstr :3129
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3129 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3129
From Windows
Test-NetConnection HOST -Port 3129
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3129

Block port 3129 in the firewall

ufw
sudo ufw deny 3129/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3129 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3129 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3129' -Direction Inbound -Protocol TCP -LocalPort 3129 -Action Block
ufw
sudo ufw deny 3129/udp
iptables
sudo iptables -A INPUT -p udp --dport 3129 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3129 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3129' -Direction Inbound -Protocol UDP -LocalPort 3129 -Action Block

Related ports

3127ctx-bridge3128Squid proxy3130icpv23131netbookmark

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