Is it possible to determine client's IP address?
To get it from SQL, you need to use Firebird 2.0 (own address), or Firebird 2.1 (anyone's):
If you use Firebird 2.0 or higher, use the RDB_GET$Context function with ('SYSTEM', 'CLIENT_ADDRESS') parameters.
If you use Firebird 2.1 or higher, you can get address of any client by selecting from the monitoring tables.
With Firebird 1.x you can try to get the information from TCP/IP stack, using netstat or lsof commands from the command-prompt. Just search for Firebird's port (3050 or gds_db).