Aprsdigi is a specialized Amateur Packet Radio (AX.25) UI-frame digipeater for the Automatic Position Reporting Systems, APRS(tm). It uses the Linux kernel AX.25 network stack as well as the SOCK_PACKET facility to listen for packets on one or more radio interfaces (ports) and repeat those packets -- with several possible modifications -- on the same or other interfaces. Aprsdigi can also use the Internet to tunnel connections among other APRS digipeaters and nodes using IPv4 or IPv6 UDP unicast or multicast.