Cisco CCNA Exam Tutorial: Why Do We Use RFC 1918 Private Address Ranges?Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 or Go To our Certification Articles Section
When you're studying to pass the CCNA, you're introduced
to "private addresses", the address ranges formally
referred to as RFC 1918 Private Addresses. (RFC stands for
Request For Comment; to see a typical RFC, just put that term
in your favorite search engine.)
There are three ranges of 1918 Private Addresses, one in
each major network class.
Class A: 10.0.0.0 /8
Class B: 172.16.0.0 /12
Class C: 192.168.0.0 /16
Be careful - these masks are not the classful network masks
you're familiar with!
The need for private address ranges arose when we started
running out of IP addresses! (A lot of us never thought that
would happen, but a lot of us used to think we’d never
need storage units bigger than floppy disks, too.) You can
imagine that as networks began to be installed in offices
and schools worldwide, the finite number of IP addresses became
a restrictive factor.
Many devices that were using these precious IP addresses
did not need to communicate with any device outside its own
local area network (LAN). Therefore, these devices could be
assigned an IP address that could be used on another device
in another LAN - but these devices would not be able to communicate
across the Internet.
It was decided to create network address ranges that would
be used exclusively for such devices. That's why when you
go from one local area network to another, you'll usually
see hosts with IP addresses from the above three ranges.
Of course, as time went on, more and more of these devices
did need to reach hosts across the Internet. That's where
NAT - Network Address Translation - comes into play. But that
is a subject for another tutorial.
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
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