Xastir's default Server Port for communicating with other processes over the network is Port 2023. Xastir listens for both TCP and UDP connections.
The server port is configured using the "Enable Server Ports" option available on the Interface Menu.
This menu option enables and disables TCP and UDP listening sockets at port 2023. You may connect other APRS(tm) clients to the TCP port in order to send/receive APRS(tm) data. Once they authenticate, they'll be able to send data to Xastir. Without authentication, they'll be able to receive every bit of TNC and INET data that Xastir receives. Note that ANY user with the proper credentials can come in on the TCP or UDP ports if they are enabled. The only one of these two ports currently that can send to RF is the UDP Server port. The TCP port cannot.
"user WE7U-13 pass XXXX vers XASTIR 1.3.3"
Connect another APRS(tm) client to that port and it should authenticate and be able to send to any server that Xastir is connected to, as well as receive packets from all ports/servers Xastir is hooked to.
You should also have a binary called "xastir_udp_client" which can send packets into the UDP listening port. Invoke it like this:
xastir_udp_client localhost 2023 <callsign> <passcode> "APRS Packet Goes Here"
Currently that will inject the packet into Xastir's decoding routines and send it to any TCP-connected clients. It will also igate it to the INET if you have igating enabled. It will send the packet out the RF ports as third-party packets only if you add the "-to_rf" flag after the passcode like this:
xastir_udp_client localhost 2023 <callsign> <passcode> -to_rf "APRS Packet"
The UDP client is useful for generating and injecting APRS packets from external scripts. It can also be used to fetch the callsign of the remote xastir server by using the -identify flag:
xastir_udp_client localhost 2023 <callsign> <passcode> -identify