--ra-param=<interface>,[mtu:<integer>|<interface>|off,][high,|low,]<ra-interval>[,<router lifetime>]
Set non-default values for router advertisements sent via an
interface. The priority field for the router may be altered from the
default of medium with eg
--ra-param=eth0,high.
The interval between router advertisements may be set (in seconds) with
--ra-param=eth0,60.
The lifetime of the route may be changed or set to zero, which allows
a router to advertise prefixes but not a route via itself.
--ra-param=eth0,0,0
(A value of zero for the interval means the default value.) All four parameters may be set at once.
--ra-param=eth0,mtu:1280,low,60,1200
The interface field may include a wildcard.
The mtu: parameter may be an arbitrary interface name, in which case the MTU value for that interface is used. This is useful
for (eg) advertising the MTU of a WAN interface on the other interfaces of a router.