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CompTIA A+ Certification All-in-One Exam Guide

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Figure 19-54 Windows 7 red X error notification icon

If you encounter this problem, first check the obvious. Run ipconfig from

the command line. Do you see an APIPA/zeroconf address, like

169.254.15.22? That’s a clear sign of a disconnect between the system and

the DHCP server. Is the cable unplugged at the system? At the wall outlet?

Then go for the less obvious: Is the NIC disabled in Device Manager? If

these checks don’t solve the problem, take a peek on the other side of the

cable. If you’re not connected to a running switch, you’re going to get the

disconnect errors.

TIP If you’re in macOS or Linux, you can use the ifconfig or ip commands

to get the same information that ipconfig gives you in Windows.

Intermittent connectivity is often the same issue but typically is harder to

figure out. Either way, read the next section to see how to get serious about

testing for these pesky connectivity problems.

EXAM TIP The CompTIA A+ 1001 exam objectives list APIPA/link local

address as a common symptom of wired and wireless network problems, but

that’s only half true. Certainly, getting an APIPA address rather than an

accurate network address points to a disconnect between the workstation and

the DHCP server that could be caused by many factors. But every computer

gets a link-local address these days. That’s just the way IPv6 works.

For the exam, though, CompTIA equates link-local addresses with APIPA

and will likely lump the two together in a troubleshooting scenario. You

know better, but don’t miss the exam question by overthinking.

Diagnosing Physical Problems

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