> 1- using TCP Stack or TELNET i can't validate if the server is a FirebirdSQL
> server even if the (3050) TCP port is active;

To do so you should read the protocoll implementation to try an
Server-Connect.

> 2- using try/except block, (FBClient/GDS32) can HALT my application

On what condition an connect does hang.

On my experience there is an immidiate error message if there is no
Server on port 3050.

The error does come after an delay if the target host is unreachable.

There also is an error if I try to connect to an differnet port with
other software listening on (e.g. SMTP).

Elmar