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Port 643 (sanity)

IANA assigns port 643 to sanity: SANity.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
sanity TCP SANity Peter Viscarola -
sanity UDP SANity Peter Viscarola -

Check what is listening on port 643

Linux: is anything listening on TCP 643?
sudo ss -tlnp 'sport = :643'
Linux: UDP 643
sudo ss -ulnp 'sport = :643'
Linux / macOS: which process owns the port
sudo lsof -nP -i :643
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':643 '
Windows (Command Prompt)
netstat -ano | findstr :643
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 643 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 643
From Windows
Test-NetConnection HOST -Port 643
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 643

Block port 643 in the firewall

ufw
sudo ufw deny 643/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 643 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 643 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 643' -Direction Inbound -Protocol TCP -LocalPort 643 -Action Block
ufw
sudo ufw deny 643/udp
iptables
sudo iptables -A INPUT -p udp --dport 643 -j DROP
nftables
sudo nft add rule inet filter input udp dport 643 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 643' -Direction Inbound -Protocol UDP -LocalPort 643 -Action Block

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