To set the runtime status of the net.ipv6.conf.default.accept_ra_defrtr kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_ra_defrtr=0
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_ra_defrtr = 0