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Cisco CCNA Certification Exam Tutorial: Prefix Notation |
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When you're preparing to pass the CCNA exam and earn this
coveted Cisco certification, you've got to be totally prepared
for the many kinds of binary and subnetting questions Cisco
may throw at you. You also have to be familiar with the different
manners in which a subnet mask can be expressed, and that’s
where your knowledge of prefix notation comes in. Prefix notation
is an alternate way to express the value of a subnet mask,
as opposed to the more familiar dotted decimal format. Not
only will you see prefix notation in Cisco documentation,
but you’ll probably see it on your CCNA exam. Consider
the following two values:
255.255.255.0
/24
Believe it or not, those two values are exactly the same.
The first mask is written out in the more familiar dotted
decimal format, and you know by looking at those first three
octets that every bit is set to "1", since the maximum
value of such an octet is 255.
The second value represents the exact same mask, only this
value is expressed in prefix notation. This particular value
would be pronounced "slash twenty-four", and the
24 represents the number of consecutive ones that are set
in the subnet mask.
Those of us who hate to type numbers are particularly appreciative
of this, since it means you'll have to type a lot less numbers
to represent a subnet mask. In addition, it's a lot easier
to discuss masks in prefix notation than dotted decimal. ("I
thought about using a two-fifty-five two-fifty-five two-fifty-five
zero mask ,but then decided to use a two-fifty-five two-fifty-five
two-fifty-five one-twenty-eight mask...")
Be sure you're comfortable with prefix notation before taking
your CCNA exam. As with Cisco documentation, you'll most likely
see masks expressed in both dotted decimal and prefix notation,
and you've got to be ready to use the both as well!
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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