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Port 637 (lanserver)

IANA assigns port 637 to lanserver.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
lanserver TCP lanserver Chris Larsson -
lanserver UDP lanserver Chris Larsson -

Check what is listening on port 637

Linux: is anything listening on TCP 637?
sudo ss -tlnp 'sport = :637'
Linux: UDP 637
sudo ss -ulnp 'sport = :637'
Linux / macOS: which process owns the port
sudo lsof -nP -i :637
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':637 '
Windows (Command Prompt)
netstat -ano | findstr :637
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 637 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 637
From Windows
Test-NetConnection HOST -Port 637
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 637

Block port 637 in the firewall

ufw
sudo ufw deny 637/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 637 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 637 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 637' -Direction Inbound -Protocol TCP -LocalPort 637 -Action Block
ufw
sudo ufw deny 637/udp
iptables
sudo iptables -A INPUT -p udp --dport 637 -j DROP
nftables
sudo nft add rule inet filter input udp dport 637 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 637' -Direction Inbound -Protocol UDP -LocalPort 637 -Action Block

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