Routing behind the mobile station (MS) is a networking feature that enables a user device to act as a router for packets to IPv4 addresses that are not directly assigned to the MS but instead exist behind it. When routing behind the MS is enabled, the Gateway GPRS Support Node (GGSN) allows packets with a source IPv4 address (uplink) or a destination IPv4 address (downlink) that is different than the MS IP address. This feature is useful in scenarios where devices behind the MS need to communicate with external networks.