Firebird remote interface vs direct file access for firebird databases

The scenario it can happen when using firebird classic (see the end of the article) You skip the remote interface (tcp/ip) and access the database directly by typing

isql-fb database path

here is my setup when i try to use the database directly or without password the server is not using the remote interface (There is no remote server/interface in the show version command)

sudo isql-fb /var/lib/firebird/2.5/data/rubyonfire.fdb
Database:  /var/lib/firebird/2.5/data/rubyonfire.fdb

SQL> show version;
ISQL Version: LI-V2.5.2.26466 Firebird 2.5
Server version:
Firebird/linux AMD64 (access method), version "LI-V2.5.2.26466 Firebird 2.5"
on disk structure version 11.2
quit;

check if the server is up with telnet localhost 3050 and then force the tcp ip method to connect using the remote interface use locahost:path 

SQL>connect "localhost:/var/lib/firebird/2.5/data/rubyonfire.fdb" user 'SYSDBA' password '********';

SQL> show version;
ISQL Version: LI-V2.5.2.26466 Firebird 2.5
Server version:
Firebird/linux AMD64 (access method), version "LI-V2.5.2.26466 Firebird 2.5"
Firebird/linux AMD64 (remote server), version "LI-V2.5.2.26466 Firebird 2.5/tcp /P12"
Firebird/linux AMD64 (remote interface), version "LI-V2.5.2.26466 Firebird 2.5/tcp )/P12"
on disk structure version 11.2