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Port 511 (passgo)

IANA assigns port 511 to passgo: PassGo.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
passgo TCP PassGo John Rainford -
passgo UDP PassGo John Rainford -

Check what is listening on port 511

Linux: is anything listening on TCP 511?
sudo ss -tlnp 'sport = :511'
Linux: UDP 511
sudo ss -ulnp 'sport = :511'
Linux / macOS: which process owns the port
sudo lsof -nP -i :511
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':511 '
Windows (Command Prompt)
netstat -ano | findstr :511
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 511 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 511
From Windows
Test-NetConnection HOST -Port 511
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 511

Block port 511 in the firewall

ufw
sudo ufw deny 511/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 511 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 511 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 511' -Direction Inbound -Protocol TCP -LocalPort 511 -Action Block
ufw
sudo ufw deny 511/udp
iptables
sudo iptables -A INPUT -p udp --dport 511 -j DROP
nftables
sudo nft add rule inet filter input udp dport 511 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 511' -Direction Inbound -Protocol UDP -LocalPort 511 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.