Hand out IPv6 with router advertisements#

You will end up with the router advertising an IPv6 prefix on a network, so devices there configure themselves. This is how IPv6 addressing normally works — there is no IPv6 equivalent of "the DHCP server hands out addresses" as the default path.

Read IPv6: what is configurable and where it is observable first.

Before you start#

The operator role and a licence.
A prefix on the interface — usually from the prefix your provider delegates (Network → IPv6 → Prefix delegation), or a static address on Network → IPv6 → Addressing.
ICMPv6 accepted in the firewall. Router advertisements are ICMPv6. A router that drops them advertises nothing.

Step 1 — Advertise a prefix#

Network → IPv6 → Router advertisements → Advertise on an interface.

Field	What to enter
Interface	the network's interface, such as the LAN
Prefixes	`::/64` — the /64 the interface holds, which follows a delegated prefix when it changes. Or a prefix of your own, such as `2001:db8:1::/64`
DNS servers	up to three; the router's own address on the interface if it answers DNS
Search domains	optional: the domain devices append to short names

Step 2 — Decide about the two DHCPv6 switches#

These are the ones people get wrong, because their names describe the protocol rather than the effect.

Switch	Tells devices
Addresses from DHCPv6	get your address from DHCPv6, not from the prefix
Other settings from DHCPv6	build your own address, and get other settings — DNS servers, domains — from DHCPv6

Neither, with a prefix and a DNS server: devices build their own addresses and use the DNS server from the advertisement. That is the simplest arrangement and the one to start from. Addresses from DHCPv6 without a DHCPv6 server leaves devices waiting for an address that never arrives; the server is on DHCP — IPv6.

Start advertising, then Apply changes in the Commit Bar, where the change reads Send router advertisements on eth0 — Prefix ::/64, DNS server ….

Step 3 — Accept ICMPv6#

All of ICMPv6, not just echo, as an input rule in the IPv6 family on Firewall: neighbour discovery and path MTU discovery live there. This rule is in the ruleset the installer writes, so on most boxes it is already present. A default-drop ruleset.

Check it worked#

From a device on the network:

bash

ip -6 addr show
ip -6 route show

An address built from the advertised prefix, and a default route via the router's link-local address, is the whole answer. On the router, Network → IPv6 → Status lists the devices that answered in its neighbour table.

Changing and stopping it#

Select the interface's row to change what is advertised. Router lifetime 0 keeps the prefixes and tells devices to stop using this router as their gateway; Disabled keeps the settings and sends nothing; Stop advertising, pressed twice, removes them. Devices keep their addresses until the prefix's lifetime runs out.