Assign only the ULA prefix on the LAN interface.
uci set network.lan.ip6class="local"
uci commit network
service network restart
Announce IPv6 default route for clients using the ULA prefix.
uci set dhcp.lan.ra_default="1"
uci commit dhcp
service odhcpd restart
Prefer IPv6 over IPv4 behind NAT66 for the ULA prefix. Specify an unassigned prefix for ULA.
NET_ULA="$(uci get network.globals.ula_prefix)"
uci set network.globals.ula_prefix="d${NET_ULA:1}"
uci commit network
service network restart
Suppress warnings about missing GUA prefix.
uci set dhcp.odhcpd.loglevel="3"
uci commit dhcp
service odhcpd restart
Disable IPv6 source filter for setups using PBR, NAT or NPT.
uci set network.wan6.sourcefilter="0"
uci commit network
service network restart