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Port 546 (DHCPv6 client)

DHCPv6 clients receive replies on UDP 546.

Well-known (system) port, 0-1023 UDP Network infrastructure Localhost or LAN only

Port 546 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

What port 546 is used for

DHCPv6 clients receive replies on UDP 546.

Security: should port 546 be open?

Localhost or LAN only. Allow on the local link for IPv6 address and DNS configuration.

IANA assignment

Service nameProtoDescriptionAssigneeReference
dhcpv6-client TCP DHCPv6 Client - -
dhcpv6-client UDP DHCPv6 Client IESG RFC 9915

Registry dates for this port: last modified 2018-05-21.

Check what is listening on port 546

Linux: UDP 546
sudo ss -ulnp 'sport = :546'
Linux / macOS: which process owns the port
sudo lsof -nP -i :546
Windows (Command Prompt)
netstat -ano | findstr :546
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 546

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 546

Block port 546 in the firewall

ufw
sudo ufw deny 546/udp
iptables
sudo iptables -A INPUT -p udp --dport 546 -j DROP
nftables
sudo nft add rule inet filter input udp dport 546 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 546' -Direction Inbound -Protocol UDP -LocalPort 546 -Action Block

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