Cisco certification candidates, particularly CCNA candidates,
must master binary math. This includes basic conversions,
such as binary-to-decimal and decimal-to-binary, 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.
Hex-to-decimal 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 #12933, is the owner of The Bryant Advantage,
home of free CCNA and CCNP tutorials, The Ultimate CCNA Study
Package, and Ultimate CCNP Study Packages. For a FREE copy
of his latest e-books, “How To Pass The CCNA” and
“How To Pass The CCNP”, visit the website and download
your free copies. You can also get FREE CCNA and CCNP exam
questions every day! Pass the CCNA exam with The Bryant Advantage!
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