To Find Client IP Address From Server.

We can use PLSQL package UTL_INADDR.
There is two procedure 1. GET_HOST_NAME or 2. GET_HOST_ADDRESS for find out local or remote HOST name or IP address.
UTL_INADDR
We can use below query to findout CLIENT IP ADDRESS.
select sid,machine,UTL_INADDR.GET_HOST_ADDRESS (machine)
from v$session
where type = 'USER' and username is not null
order by sid;
If you are getting below error message then modify above code little bit.
ERROR at line 1:ORA-29257: host xxxxxxxxxxxxxxxxxx unknown
ORA-06512: at "SYS.UTL_INADDR", line 19
ORA-06512: at "SYS.UTL_INADDR", line 40
ORA-06512: at line 1
Modified code
select sid, machine,
UTL_INADDR.get_host_address (substr(machine,instr(machine,'\')+1)) ip
from v$session
where type='USER' and username is not null
order by sid;