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Port 21801 (sal)

IANA assigns port 21801 to sal: Safe AutoLogon.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference
sal TCP Safe AutoLogon WM Software Inc. -

Registry dates for this port: registered 2022-07-05, last modified 2022-07-06.

Check what is listening on port 21801

Linux: is anything listening on TCP 21801?
sudo ss -tlnp 'sport = :21801'
Linux / macOS: which process owns the port
sudo lsof -nP -i :21801
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':21801 '
Windows (Command Prompt)
netstat -ano | findstr :21801
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 21801 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 21801
From Windows
Test-NetConnection HOST -Port 21801

Block port 21801 in the firewall

ufw
sudo ufw deny 21801/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 21801 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 21801 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 21801' -Direction Inbound -Protocol TCP -LocalPort 21801 -Action Block

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