Port 8231 (hncp-udp-port)

IANA assigns port 8231 to hncp-udp-port: HNCP.

Registered (user) port, 1024-49151 UDP

Port 8231 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

IANA assignment

Service nameProtoDescriptionAssigneeReference

hncp-udp-port UDP HNCP IESG RFC 7788

Registry dates for this port: registered 2016-01-13.

Linux: UDP 8231

sudo ss -ulnp 'sport = :8231'

Linux / macOS: which process owns the port

sudo lsof -nP -i :8231

Windows (Command Prompt)

netstat -ano | findstr :8231

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 8231

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 8231

ufw

sudo ufw deny 8231/udp

iptables

sudo iptables -A INPUT -p udp --dport 8231 -j DROP

nftables

sudo nft add rule inet filter input udp dport 8231 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 8231' -Direction Inbound -Protocol UDP -LocalPort 8231 -Action Block

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