In the default stateless operation mode, the DHCPv6 server on the modem's eRouter distributes additional configuration (e.g. DNS servers) only, while Router Advertisement distributes the /64 prefix (within the delegated /56 or /57 prefix), which devices construct their IPv6 addresses from. In the stateful operation mode, IPv6 addresses are distributed using DHCPv6 as well. Android does not support stateful DHCPv6 and will not be able to obtain an IPv6 address using this configuration, therefore the device will fall back to IPv4.