Cisco CCNA Certification: The Joy Of Hex
by: Chris Bryant, CCIE #12933
Cisco certification candidates, particularly CCNA candidates, must master
binary math. This includes basic conversions, such as binarytodecimal and
decimaltobinary, as well as more advanced scenarios involving subnetting and
VLSM.
There’s another conversion that might rear its ugly head on your Cisco
exam, though, and that involves hexadecimal numbering.
Newcomers to hexadecimal numbering are often confused as to how a letter of
the alphabet can possibly represent a number. Worse, they may be intimidated
– after all, there must be some incredibly complicated formula involved with
representing the decimal 11 with the letter “b”, right?
Wrong.
The numbering system we use every day, decimal, concerns itself with units
of ten. Although we rarely stop to think of it this way, if you read a decimal
number from right to left, the number indicates how many units of one, ten, and
one hundred we have. That is, the number “15” is five units of one and one
unit of ten. The number “289” is nine units of one, eight units of ten, and
two units of one hundred. Simple enough!
Hex numbers are read much the same way, except the units here are units of
16. The number “15” in hex is read as having five units of one and one unit
of sixteen. The number “289” in hex is nine units of one, eight units of
sixteen, and two units of 256 (16 x 16).
Since hex uses units of sixteen, how can we possibly represent a value of
10, 11, 12, 13, 14, or 15? We do so with letters. The decimal “10” is
represented in hex with the letter “a”; the decimal 11 with “b”; the
decimal “12” with “c”, “13” with “d”, “14” with “e”,
and finally, “15” with “f”. (CCNA candidates will remember that a MAC
address of “ffff.ffff.ffff” is a Layer 2 broadcast.)
Practice Your Conversions For Exam Success
Now that you know where the letters fall into place in the hexadecimal
numbering world, you’ll have little trouble converting hex to decimal and
decimal to hex – if you practice.
How would you convert the decimal 27 to hex? You can see that there is one
unit of 16 in this decimal; that leaves 11 units of one. This is represented in
hex with “1b” – one unit of sixteen, 11 units of one.
Converting the decimal 322 to hex is no problem. There is one unit of 256;
that leaves 66. There are four units of 16 in 66; that leaves 2, or two units
of one. The hex equivalent of the decimal 322 is the hex figure 142 – one
unit of 256, four units of 32, and 2 units of 2.
Hextodecimal conversions are even simpler. Given the hex number 144, what
is the decimal equivalent? We have one unit of 256, four units of 16, and four
units of 4. This gives us the decimal figure 324.
What about the hex figure c2? We now know that the letter “c” represents
the decimal number “12”. This means we have 12 units of 16, and two units
of 2. This gives us the decimal figure 194.
Tips For Exam Day
Practice your binary and hexadecimal conversions over and over again before
you take your CCNA exams. Binary math questions come in many different forms;
make sure you have practiced all of them before exam day. The number one reason
CCNA candidates fail their exam is that they’re not prepared for the
different types of binary math questions they’re going to be asked, and that
they aren’t ready for hexadecimal questions at all.
You don’t have time to learn how to do in on exam day. You’ve got to be
ready before you go into the exam room, and the only way to be ready is a lot
of practice.
Finally, make sure you read the question carefully. You’ve got hex,
decimal, and binary numbers to concern yourself with on your CCNA exams. Make
sure you give Cisco the answer in the format they’re looking for.
About The Author
Chris Bryant, CCIE (TM) #12933, has been active in the Cisco
certification community for years. He has written several books that
have helped CCNA candidates around the world achieve the coveted CCNA
certification, including several concentrating on binary math
conversions and subnetting questions that the average CCNA candidate
will need to answer on their CCNA exams.
He is the owner of The Bryant Advantage (http://www.thebryantadvantage.com)
where he teaches affordable worldclass CCNA courses via the Internet.
He’s proud to have helped CCNA candidates around the world achieve
their career goals. Mr. Bryant’s books and courses are sold on his
site, on eBay, and on several other major Cisco certification sites.

