Port 5683 (CoAP)

Constrained Application Protocol for low-power IoT devices; 5684 is CoAP over DTLS.

Registered (user) port, 1024-49151 UDP IoT and devices Do not expose to the internet

Port 5683 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

What port 5683 is used for

Constrained Application Protocol for low-power IoT devices; 5684 is CoAP over DTLS.

Do not expose to the internet. Open CoAP devices are used for UDP reflection attacks; do not expose them.

Service nameProtoDescriptionAssigneeReference

coap TCP Constrained Application Protocol (CoAP) IESG RFC 8323

coap UDP Constrained Application Protocol IESG RFC 7252

Registry dates for this port: registered 2011-06-13, last modified 2013-07-25.

Linux: UDP 5683

sudo ss -ulnp 'sport = :5683'

Linux / macOS: which process owns the port

sudo lsof -nP -i :5683

Windows (Command Prompt)

netstat -ano | findstr :5683

Windows (PowerShell)

Get-NetUDPEndpoint -LocalPort 5683

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

nc -vzu -w 5 HOST 5683

ufw

sudo ufw deny 5683/udp

iptables

sudo iptables -A INPUT -p udp --dport 5683 -j DROP

nftables

sudo nft add rule inet filter input udp dport 5683 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 5683' -Direction Inbound -Protocol UDP -LocalPort 5683 -Action Block

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