Port 4754 (gre-in-udp)

IANA assigns port 4754 to gre-in-udp: GRE-in-UDP Encapsulation.

Registered (user) port, 1024-49151 UDP

Port 4754 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

gre-in-udp UDP GRE-in-UDP Encapsulation IESG RFC 8086

Registry dates for this port: registered 2016-10-05.

Linux: UDP 4754

sudo ss -ulnp 'sport = :4754'

Linux / macOS: which process owns the port

sudo lsof -nP -i :4754

Windows (Command Prompt)

netstat -ano | findstr :4754

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 4754

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

nc -vzu -w 5 HOST 4754

ufw

sudo ufw deny 4754/udp

iptables

sudo iptables -A INPUT -p udp --dport 4754 -j DROP

nftables

sudo nft add rule inet filter input udp dport 4754 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 4754' -Direction Inbound -Protocol UDP -LocalPort 4754 -Action Block

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