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Port 638 (mcns-sec)

IANA assigns port 638 to mcns-sec.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
mcns-sec TCP mcns-sec Kaz Ozawa -
mcns-sec UDP mcns-sec Kaz Ozawa -

Check what is listening on port 638

Linux: is anything listening on TCP 638?
sudo ss -tlnp 'sport = :638'
Linux: UDP 638
sudo ss -ulnp 'sport = :638'
Linux / macOS: which process owns the port
sudo lsof -nP -i :638
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':638 '
Windows (Command Prompt)
netstat -ano | findstr :638
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 638 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 638
From Windows
Test-NetConnection HOST -Port 638
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 638

Block port 638 in the firewall

ufw
sudo ufw deny 638/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 638 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 638 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 638' -Direction Inbound -Protocol TCP -LocalPort 638 -Action Block
ufw
sudo ufw deny 638/udp
iptables
sudo iptables -A INPUT -p udp --dport 638 -j DROP
nftables
sudo nft add rule inet filter input udp dport 638 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 638' -Direction Inbound -Protocol UDP -LocalPort 638 -Action Block

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