Cisco Packet Tracer
Cisco Packet tracer is not a requirement for passing CCENT or CCNA, but having the ability to practice pre-built simulations is essential for continuous learning.
If you are interested in obtaining this software you must be apart of the Cisco Networking Academy.
You can be apart of this group by being a instructor, student, or alumni.
Here is a link to the Cisco Networking Academy.
But if you get the chance to use it I recommend you practicing with the IOS on the switches/routers so the simulations will feel more familiar.
All Cisco certifications tests now involve simulations of some sort!