Router Advertisements

radvd (the service responsible for this functionality) is the router advertisement daemon for IPv6. It listens to router solicitations and sends router advertisements as described in “Neighbor Discovery for IP Version 6 (IPv6)” (RFC 4861). With these advertisements hosts can automatically configure their addresses and some other parameters. It also defines “Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)” (RFC6775). They also can choose a default router based on these advertisements.

Router Advertisements (Mode)

The mode selection contains some predefined settings for radvd, which influence a set of configuration options and are intended for specific implementation scenarios. They define the type of client deployment used in your network.

Router Only	Only advertise this router, clients are using static IPv6 addressses
Unmanaged	Clients will use Stateless Address Autoconfiguration (SLAAC), without other (non-address) information being provided.
Managed	Stateful configuration, address configuration provided by DHCPv6
Assisted	Stateful configuration, address configuration provided by DHCPv6, although advertised routes can also be used on Stateless Address Autoconfiguration setups (SLAAC).
Stateless	Clients will use Stateless Address Autoconfiguration (SLAAC)

A detailed overview of the radvd settings determined by the mode can be found below:

scope	Settings	Router Only	Unmanaged	Managed	Assisted	Stateless
Per interface	AdvManagedFlag			X	X
Per interface	AdvOtherConfigFlag			X	X	X
Per prefix	AdvOnLink		X	X	X	X
Per prefix	AdvAutonomous		X		X	X

Note

Technical details about the options can be found in the man page of radvd

General

Priority	The preference associated with the default router, as either “low”, “medium” (default), or “high”.
RA Interface	Interface to use prefix from.
Advertise Default Gateway	uses `AdvDefaultLifetime` to disable advertising as default router when unset.
Advertise Routes	Advertise more specific specific routes to the clients.

DNS

For supported clients, DNS settings can also be propagated by radvd as detailed in RFC 8106

DNS servers	Define which dns servers to publish to the clients, either the ones defined here or (when Use the DNS settings of the DHCPv6 server is set) the ones defined in the DHCPv6 server for this interface. (`RDNSS` in `radvd`)
Domain search list	Domain search list to push to the clients, when not specified the local domain name from this firewall is used. (`DNSSL` in `radvd`)

Intervals

The time between unsolicited multicast router advertisement can be configured, using the following settings, usually these are left default.

Minimum Interval	The minimum time allowed between sending unsolicited multicast router advertisements from the interface, in seconds. Must be no less than 3 seconds and no greater than 0.75 * “Maximum Interval”.
Maximum Interval	The maximum time allowed between sending unsolicited multicast router advertisements from the interface, in seconds. Must be no less than 4 seconds and no greater than 1800 seconds.