If the tunnel is inspected (by setting IPV4_TUNNELING to True), the IPv4 connections inside the tunnel are identified. This shows the actual destination IPv4 address, but since the source IPv4 addresses are reused, they cannot be used to identify subscribers or correctly account traffic.
With the system configuration value TUNNELING_DSLITE_SUPPORT set to True (IPV4_TUNNELING must also be enabled), PacketLogic will look inside the tunnel and account each connection inside as an IPv6 connection, using the IPv6 source address as the source address for all connections. This allows identifying subscribers with the source address. The IPv4 destination IP address is used as destination of the connection. The destination address is converted to an IPv6 address using a standard prefix.