Port 546: DHCPv6 client
Port 546 is the DHCPv6 client port, over UDP. It is the IPv6 counterpart of port 68: a host receives DHCPv6 advertise and reply messages here, and sends its solicit and request messages to a server on port 547.
| Port number | 546 |
|---|---|
| Service | DHCPv6 client |
| Protocol | UDP |
| Category | Core services |
| Default encryption | No |
| IANA service name | dhcpv6-client |
| IANA transports | TCP, UDP |
| Used in practice | UDP |
Which ports are related to port 546?
The port a reader usually needs next is the encrypted or plaintext twin of this one, so those are listed first rather than buried in a generic list.
What commonly listens on port 546?
- dhclient -6, dhcpcd and systemd-networkd on Linux
- The DHCPv6 client built into Windows, macOS, iOS and Android
How do I check whether port 546 is open?
Port 546 is UDP, which changes the answer: there is no handshake to complete, so nothing outside the host can prove the port is open. Asking the host itself is the reliable route.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | sudo nmap -sU -p 546 example.com | UDP has no handshake, so there is nothing to complete. nmap infers the state from whether an ICMP port-unreachable comes back, needs root, and is slow and easy to misread. A silent port may be open, filtered, or simply not replying to a probe it does not recognise. |
| What is listening locally? | ss -ulnp | grep ':546 ' | Shows the UDP socket bound to port 546. This is the reliable way to answer the question, because you are asking the host itself rather than guessing from outside. |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
Does DHCPv6 use ports 67 and 68?
No. DHCPv6 uses UDP 546 for the client and UDP 547 for the server. Ports 67 and 68 are IPv4-only, so a firewall configured for IPv4 DHCP will not pass DHCPv6 traffic.
Why does DHCPv6 use multicast instead of broadcast?
IPv6 has no broadcast address. A DHCPv6 client sends to the All_DHCP_Relay_Agents_and_Servers multicast group ff02::1:2 on port 547 instead, which reaches servers on the link without waking every host.
What is port 546 used for?
Port 546 is the DHCPv6 client port, over UDP. It is the IPv6 counterpart of port 68: a host receives DHCPv6 advertise and reply messages here, and sends its solicit and request messages to a server on port 547.
Is port 546 TCP or UDP?
IANA assigns port 546 on TCP, UDP. In practice it carries UDP. As with the IPv4 DHCP ports, the TCP registration is unused. DHCPv6 is UDP only.
Is port 546 secure?
Port 546 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 546 on my firewall?
Only if you specifically need DHCPv6 client. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.