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CCNA:
Cisco Certified Network Associate Study Guide
A hub forwards all
packets to all ports while a switch learns to associate MAC addresses
with ports to make more efficient one-to-one connections. This is one
of the less arcane facts you'll learn from this study guide. Here's a
more arcane one: The available cable ends for Cisco routers are EITA/TIA-232,
EIA/TIA-449, V.35(for CSU/DSU), X.21(for X.25) and EIA-530. Pay close
attention because you will be tested. An example multi-choice question
asks, "What Cisco layer provides segmentation of contention networks?".
Your choices are Access, Physical, Network, Distribution, Core, Transport,
Data link.
This study guide highlights
the differences between internetworking as a theoretical study and its
implementation in the real world. This is the activity for which Cisco
sells routers, hubs and switches. Reading this guide to is to glimpse
the elephant on whose back rests the virtual world. It's fascinating and
hermetic. It contains the spells the Net wizards use to abolish distance.
Like all magic, it
is both precise and arbitrary. While 10Base2 can support a bus up to 185m
long with 30 hosts 10Base5 can run to 500m and 208 users. But not 501m
or 209 hosts because then the magic won't work. This is an excellent study
guide for those who find hardcore technology capable of handling millions
of events in tiny slivers of a second with utter reliability for months
on end utterly fascinating.
Read the section on
how the spanning tree protocol prevents network loops forming. By the
way, did you know IEEE 802.1d STP supported by Cisco is incompatible with
inventor DEC's version? You will. --Steve Patient
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