In reply to Raja.

Hi Raja,
Confidence can be difficult, particularly on your first Cisco exam. First off, given your question, I'd suggest that you consider taking the two-exam path to CCNA by passing the ICND1 exam and then the ICND2 exam. That lets you break the material in half, with less volume to study for.

Second, practice applying your knowledge. That means: lots of repetition doing labs, lots of practice questions, lots of paper exercises, and any other review exercises that you can find. And when you answer a practice question and don't confidently know the answer, stop, research, and figure out the details until you are confident in the answer.

Finally, when working through that final preparation, engage at the Cisco Learning Network. Look around for posts of people asking how they gained confidence, what they did that worked to help them pass, and so on. There are lots of prior posts in which people state what they did that worked for them.

On configuration, pick the top 10-12 topics that can be configured, and practice them on paper in your spare moments, until you can do those in your sleep.

And of course, practice sub netting and the related math until it's automatic.

That sounds like a lot, and it is. But if you can get the right answer on sub netting math every time, configure the major topics correctly and quickly every time, and you fill in lots of holes in your knowledge by using lots of practice questions, then your confidence should grow.

Hope this helps!
Wendell