The Oracle server isn't "bound" to an IP address. The listener can "listen" on any number of IP addresses.
With Net8 Assistant or Net Manager (according to your version) you can configure the "Listening Locations" and add as many IP address/port combinations as you like. (Using lsnrctl you can RELOAD the listener configuration without stopping anything).
Doing it without the GUI: In listener.ora you have multiple (ADDRESS = . . . . . . ) lines.
Unless you are using a names server, all the clients will need to have both addresses configured in their tnsnames.ora (multiple (ADDRESS = . . . ) or Net Assistant/Manager again).