Step 2: Network+ - CompTIA Network+ Certified Professional
certification goes a step above A+.
With Network+ you show proficiency with a variety of networking technologies.
This does not go in depth about operating systems,
but does look at ways of moving the data around.
For anyone who will be maintaining the physical plant of a network,
this knowledge is a must.
"Network+ Study Guide (3rd Edition)"
will give you good coverage of the material on the test.
If you are experienced with network technology, a quick gloss of the material should be enough.
If you are new to computer networks, study, study, and then study some more.
There are a lot of different technologies to know about here,
and you need to at the least be able to identify many of them.