How many times have we installed Oracle any version on windows or unix (when the IP address is not static) and then found that even though you can connect to Database on the server through sqlplus it is not accessible on other machines.
Personally there used to be a time in my previous organisation when most business and technical consultants installing oracle were clueless and ended up only talking to the database on their machine.
Oracle has a file called listner.ora in the directory $ORACLE_HOME\NETWORK\ADMIN
Here is the file from one of the installation
Notice that the server has the IP address 10.91.1.105 in this case. That's it ! Now how to check if your Oracle server is accepting connections? Simple my favourit utility is nmap. Just scan the ports on the server and the port (in our case the default 1521) will be open.
That's it !