Connectivity problem : client with NAT 1-1

I have a PC in a 'Housing farm' with a Client Oracle 8.17, this PC has a NAT 1-1 (on Internet is seen as x.x.x.x, in internal 'housing farm' net as y.y.y.y). The Oracle 8.17 server (placed in my company) has a NAT 1-1 (on Internet a.a.a.a, in my company internal net b.b.b.b)

I am not able to have Client/server communicated ... and I have never had problems with other 'Housing farm' without NAT 1-1

The Client signals me ORA-12535 (Connect Timeout), on the Log of the Server Listener for every attempt I find a TNS-12502 series (No Connect_data Was Passed To The Listener).

Client TNSnames.ora and Server Listener.ora seems OK (see below), suggestions ?

======TNSnames.ora (client) ============== orcl =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = a.a.a.a (PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = orcl)

)
)

=======listener.ora (server) =============== LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = b.b.b.b )(PORT = 1521))
)
)
(DESCRIPTION =
(PROTOCOL_STACK =
(PRESENTATION = GIOP)
(SESSION = RAW)

)
(ADDRESS = (PROTOCOL = TCP)(HOST = b.b.b.b )(PORT = 2481))
)
)

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = D:\new817)
(PROGRAM = extproc)

)
(SID_DESC =
(GLOBAL_DBNAME = orcl)
(ORACLE_HOME = D:\new817)
(SID_NAME = orcl)

)
)

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