Given a scenario, troubleshoot wired and wireless networks with appropriate tools: CompTIA A+ Exam 220-901 sub-objective 4.4

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Detailed (and official) description of CompTIA A+ sub-objective 4.4:

4.4 Given a scenario, troubleshoot wired and wireless networks with appropriate tools.

Common symptoms
No connectivity
APIPA/link local address
Limited connectivity
Local connectivity
Intermittent connectivity
IP conflict
Slow transfer speeds
Low RF signal
SSID not found

Hardware tools
Cable tester
Loopback plug
Punch down tools
Tone generator and probe
Wire strippers
Crimper
Wireless locator

Command line tools
PING
IPCONFIG/IFCONFIG
TRACERT
NETSTAT
NBTSTAT
NET
NETDOM
NSLOOKUP

Welcome to ExamNotes by CertBlaster! Today we will look at wired and wireless networks and connectivity.

What are some of the more common connectivity issues? How can we address them?
Common Symptoms

No connectivity

Generally when we discuss connectivity, it is in wireless context. We will look at all aspects of the wireless connection from the SSID to channel selection.

APIPA/link local address

APIPA/ Link Local Addressing.is used to assign an IP address to a client. The Windows nodes on a network will self-assign non-routable addresses to themselves until server is able to provide an address.

Limited & Local Connectivity

Local connectivity and intermittent connectivity are all addressed with the same basic troubleshooting methods.
You will begin by trying to access a known good address on your local network this will help you determine whether your problem is with the physical network or the programs and protocols being used. Now if wired check the indicator status if the lights are on and flickering data is moving.
Next you’ll want to check neighboring computers for signs of the same problem. You need to determine whether you have a problem wilt one PC or 20. The troubleshooting methods are different.
If you are able to access some but not all of the available network resources, determine the accessibility and see if there is a pattern. Perhaps a bad network segment or device can be isolated as the point of failure.
Once you have narrowed down your problem to a specific area in your network, rule out issues with your internet service provider and its installed equipment.
Check the IP address assigned to the device. If it starts with 169.254.xxx.xxx you know it has an assigned an APIPA address and cannot communicate with the DHCP server.

To summarize:

1) Check lights on NIC and devices.
2) Test or swap out the cable.
3) Check switches and indicator lights on wireless connections.
4) Also on wireless connections Be aware of Radio power and frequency issues including line of sight
5) Start the next phase by deciding if you want to do the command line interfaces first or the programs. OK Command line it is. Open a command prompt .by clicking the icon or typing cmd in the search window.
6) We will use a few commands and varieties to diagnose the NIC and establish its relative location. First we check that the NIC its Drivers and the protocol stack are functioning properly. We’ will ping the localhost be name (ping localhost) and number (ping 127.0.0.1). Then a common internet address, most DNS servers will in all probability have looked up google recently. Its IP address is surprisingly simple. The IP address is 8.8.8.8. Ping that to validate connectivity.

IP Conflict

An IP Conflict occurs when two IP based machines use the same address. Duplicate addresses are not tolerated by the TCP/IP addressing scheme.

Other IP related issues

One interesting way to give your connection little poke is to use stock utilities like variations on the ipconfig utility. You can test the settings on your new DHCP server by using it to create Renew and Refresh the IPv4 and IPv6 addresses. Using this process the addressing can be systematically modified whenever necessary.

Slow transfer speeds

In a situation where your resources are impacted by the number of users on a segment or link. Your advertised connection speed is measured while no other devices are competing for the resources. You will find that as the number of users increases the comparative speed will decrease. You want to be aware of the number and type of connections in use by your device at any given time. Monitor and end any app that is using resources and not proving a useful service.

Low RF signal

When you encounter nominal RF signals it is very difficult for your devices to perform up to their optimal rates. As the power levels drop on the radio you will see a directly relational decrease in the performance. Observe the Linksys WAP for low/no power.

Windows screenshot of weak RF showing on same image as wireless open
Weak RF showing on same image as wireless open

SSID not found

In many cases it is advisable to hide your SSID from the prying eyes of the internet. If you think about it, you are providing would be attackers with 50% of the information necessary to access your wireless network. Here is a good look at Windows Wireless settings available from the Taskbar.

Windows screenshot of wireless open
Screenshot of wireless open

Check the warning that comes from your cable provider. Open season! If the connection has to be “Open” then you should not broadcast the address.

Hardware Tools

Here is a rundown on the tools and programs that will help you stay secure.
Loopback plug First we have a loopback plug. An indispensable item for checking a devices’ interfaces.

Cable tester

A good cable tester has the capacity to test the cable pairs used with RJ-45 cables/connectors for continuity and complete sequencing. It enables you to verify the electrical connections in a cable or other wires. See below close up.

photo of cable tester for CompTIA Aplus exam
Cable tester

Punch down tool

A punch down tool comes in quire handy when you are working is the tight spaces of a wiring closet. It has the capability of being able to generate enough force to secure your cable but also trim any excess.

photo of yellow punch down tool for aplus exam
Punch down tool

Tone generator and probe

This device is only effective when used as a pair, helps you trace wires through walls, plenums and other seemingly impossible spaces. The sending unit applies a uniform tone to the cable, which the receiver is capable of detecting.

Photo of yellow tone and probe
Tone and probe

Wire strippers

With a specialized notch for each relevant wire gauge, this device can cut through the insulation only while leaving the copper core of the wire intact.

Photo of yelloe and black wire stripper
Wire stripper

Crimper

A wire crimper is used to terminate (put the connectors on) network cables. The detailed close-up here shows that this crimper is designed for use on 8pair, (RJ-45) and 6 Pair, (RJ-11) cables.

photo of black and red cable crimper for exam objective 4.2
Cable crimper

Wireless locator

Hardware devices that are capable of scanning the environment and capturing details about the wireless frequencies in use, their strength range and channels. Along the same vein but at a lower technical level if you have ever used your wireless remote to find your car, here is the next Generation on that concept. Roughly the same size and shape to fit your keyring this device enables you to find your lost keys.

Command Line Tools

PING

This command line tool enables you to determine if you have a connection to another device on the network.

IPCONFIG/IFCONFIG

Ipconfig (ifconfig in Linux) displays the host’s IP configuration.

TRACERT

Tracert is used at the command line to display the path your data takes to a particular host on the network or internet. Traceroute is the Linux version of this command.
NETSTAT – at the command line NETSTAT is used to display the network statistics of your TCP traffic.

NBTSTAT

Designed to diagnose NetBIOS traffic, NBTSTAT is useful in troubleshooting NETBIOS name resolution problems.

NET

This one is like the Swiss army knife of command line networking utilities. When used at the command line there are a variety of switches available, enabling you to display network connections and even map networked resources as drives on your local machine.

NETDOM

NETDOM is a command line tool allowing administrators to manage Active directory domains and trusts.

NSLOOKUP

NSLOOKUP is a specialized command line Query tool. It is used to obtain any DNS information through the use of command modifiers and switches. It can return a great deal of DNS data.

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That’s all for Objective 4.4. Good luck on the test!

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