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Port 5681 (ncxcp)

IANA assigns port 5681 to ncxcp: Net-coneX Control Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ncxcp TCP Net-coneX Control Protocol Ryan Werber -
ncxcp UDP Net-coneX Control Protocol Ryan Werber -

Registry dates for this port: registered 2006-06.

Check what is listening on port 5681

Linux: is anything listening on TCP 5681?
sudo ss -tlnp 'sport = :5681'
Linux: UDP 5681
sudo ss -ulnp 'sport = :5681'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5681
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5681 '
Windows (Command Prompt)
netstat -ano | findstr :5681
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5681 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5681
From Windows
Test-NetConnection HOST -Port 5681
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5681

Block port 5681 in the firewall

ufw
sudo ufw deny 5681/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5681 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5681 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5681' -Direction Inbound -Protocol TCP -LocalPort 5681 -Action Block
ufw
sudo ufw deny 5681/udp
iptables
sudo iptables -A INPUT -p udp --dport 5681 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5681 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5681' -Direction Inbound -Protocol UDP -LocalPort 5681 -Action Block

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