This read-write enumeration configures whether reverse tunneling is preferred, set(1), or not, notSet(2), for the modem's mobile-IP data sessions. An admin enables reverse tunneling when packets from the mobile node need to be routed back through the home agent rather than sent directly, often required by networks that filter or reject topologically incorrect source addresses. For example, in a network where routers along the path drop packets whose source address doesn't match the local subnet, an admin would set this to set(1) to force traffic back through the home agent tunnel.