Can anybody tell me how important subnetting is to the 70-218? I am using the QUE training guide (ISBN 0-7897-2766-

 of which is over 1000 pages and I seem to be running into a lot of subnetting problems. And the fact is I suck at this right now. Can I just memorize tables and take a hit on what I don't know about it. I mean, I'm good at all the other topics. How difficult are the DNS problems. This book takes the details to a new level above the 70-215 test and I hear some people say on here that the 218 is "just a review". Hope to get some feedback. I always over prepare for these things and get near 900 on all my tests. Thanks in advance.