One of my networking classes included the basics of troubleshooting a network connection. It included basic command line tools that really were very easy to use and understand. Most of the students thought they were fun to use.

Knowing these commands before having to deal with the frustration of a network connection problem is not a bad idea. A working connection shows you what is supposed to happen. If you see something different, you will know something is up. When problems strike, at the least you can get an idea of what is going on.

Step 0: Check the Cords & Power

The first thing you should always do is check to make sure everything is plugged in: your computer, router, device, etc. Many laptops have a button to turn off the wireless connection; the icon looks like a signal tower. When in doubt, read the manual (which you can often download from the manufacturer’s website). Bear in mind, we all forget this step at some point, so do not feel too silly when it happens to you.

Step 1: Ping Yourself

You want to test that your machine is working properly. To do this, you want to ping yourself. You use the loop-back address (127.0.0.1) to do this. Pinging the loop-back address tests to make sure software on your computer is working properly. Typically, if something is not working at this stage, you may just need to restart your computer.

ping
http://www.ghacks.net/2011/05/12/network-troubleshooting-basics-the-ping-command/

Step 2: Ping Your Router (AKA: the Default Gateway)

The next step would be to ping your router. You can find your router’s IP address with ipconfig as well (it should be on the bottom of the unit and listed in the manual too). Remember that ipconfig lists your router as the “Default Gateway.” It is very likely to be 192.168.1.1 or a similar number.

This is done to test if your router is responding. If it is not, and you have already checked to make sure it is on, then it may need to be turned off and turned on. Every once in a while it may need a refresh. If the problem continues, contact you ISP for assistance to see if they can help.

Note: Routers, like anything else in the IT world, will someday fail. There is a chance that this has happened. Your ISP help desk should be able to help you determine this. If the router is one of theirs, they will likely send you out a new one.

Step 3: Ping Yourself with Your IP Address

We want to test to make sure everything is working correctly between your router and your computer. To do this, ping your IP address. It is listed in the ipconfig command at the same time the router IP number is. If this works, you can be pretty confident that a problem is outside your home (or maybe small office) network.

Step 4: Ping and Tracert Outside Your Network

From here, you want to test something outside your network. In a medium or larger network setting, a server on another branch of the network will do. For a home network, the Internet is often your only option. Since chances are the problem is that one or more websites are (or seem) down, this is a logical thing to check.

You can use a few different tools. First try the ping command because it is the fastest. It will only tell you if the site is working or not. For more detailed information, use tracert and pathping. They can give a better idea of what is going on. For instance, if you can reach your router, but no further, the node that connects you to the Internet may be down: an ISP issue. If you can reach only a couple (one or two) steps past your router, then it still is probably an ISP issue. Your Internet is down. If you can reach a lot further, the site may be having issues (see is Facebook down, ways to check if a website is really down, for pointers) There even is a chance that other sites, either from the same proximity or even hosting service, are having the same problem. If it is an e-commerce site, there may be a number to call, but there probably is not much to do besides wait. At least you know where the problem is.

Parting Thought

On a parting note, one other benefit of trying these commands out on a nice day like today is that it creates a positive mental association with the tools. That might change with enough problems, but they are worthy of a good first impression. Having the skills to deal with a problem ahead of time is always a good idea.

The Ipconfig Command Basics

The ipconfig command gets its name from the acronym IP (Internet Protocol) and a shortened term for configure. Understanding this served as a mnemonic device for me when I was first learning networking. It is used to display and configure your connection to the Internet. This tutorial will focus on the display and what that means.

Deciphering the Information

To get to ipconfig, we have to get to the command line.

• Click Start, click Run, type in “cmd” & hit enter.
• Type in ipconfig & hit enter. (you can use ipconfig /all for detailed information)

You will get a screen that looks like this.

To find your router’s IP number, look next to “Default Gateway” (listed last). For a mnemonic, think of the router as your gateway to the Internet or another network. To find your computers’ IP number, look next to “IP Address”. Do not worry about the other information like the subnet mask.

In this case, the computer number is 192.168.1.4 while 192.168.1.1 is the router number. It is common for 192.168.1.1 or 192.168.0.1 to be the router’s IP address. There are a few reasons for this, which were covered in a previous article.

Ping Your Router (Default Gate)

We are using the ipconfig command so that we can get the IP number of the router. As discussed at the end of the last article on the ping command, we want to ping our router. If we can ping it, then it should be working properly.

To do this, type in ping and the router (default gateway) number as shown.

Some Possible Problems

Consider a case where the connection to the Internet seems down. If you cannot ping the router, or the ipconfig command says the default gateway is 0.0.0.0, then the problem may be in the router. The first thing to check is whether the router is on and everything is plugged in. The next thing to try would be to either restart the computer or to try and ping the router from another computer. From here, you may want to call your ISP’s help line and let them know what you have tried. An experienced user may restart the router; I have found that mine needs this from time to time. For a beginner, it is better to get some help. You will learn from the experience.

There is a possibility that your router may be failing. That has happened to me once before. Fortunately, a friend helped me troubleshoot the device, so stay in touch with networking pals. The culprit may likely have been heat from a lack of proper ventilation. Be sure your router has proper air flow. While they may run warm, if they are hot to the touch, it may be bad for the device (check your manual or consult your manufacturer).

ipconfig Command Line Options

Ipconfig has several command line options that you can utilize. You can display all of them with the command ipconfig /?. Here is a short selection of the most common uses.

• ipconfig /release – Releases all IPv4 addresses (requires DHCP)
• ipconfig /renew – Renews all IPv4 addresses (requires DHCP)
• ipconfig /flushdns – Flushes the DNS cache

Linux & Mac Use Ifconfig & Route -n

For those running Linux or are on a Mac, the commands to use are ifconfig and route -n. Is ifconfig identical to ipconfig? No. The ifconfig command will show you your computer’s IP number and other information. You just type in the command, ifconfig, into the terminal to find out information about how your computer connects to the Internet. To get your router’s IP number, you use the route command with a -n (netstat -r should work too). Both are shown in the screen shots. Make sure you use lowercase letter; the commands are case sensitive. (Side Note: Linux also has a iwconfig command for wireless specific tweaking (e.g. frequency).)

Just a note about the Mac ifconfig command. We are using it to view network settings, which is fine. In doing research for this article, I read that it is not advised to use this to change settings. From what I read, it works, but with possible complications.

Closing

We use ipconfig to find the router’s IP number. Once you have that, you can ping the router to test if it is responsive. The problem with the ping command is that, while it is fast, is doesn’t give you a lot of information. For that, we use the tracert command, which will be covered next.

It is probably a good idea to test if IPv6 is already available on the operating system. An easy option to find out is the ipconfig command which displays network information in a command line window. To run the command press Windows-R, type cmd and hit enter. This opens the Windows command prompt. Now use the command ipconfig to find out if IPv6 is available on the computer. Please note that the following screenshot is showing ipconfig on Windows 7.

If you do not see an entry IPv6 Address in the listing it is not enabled and needs to be installed. The easiest way to install the IPv6 protocol under Windows XP is from the command prompt. Enter the following commands separately and press return after each of them:

• netsh
• interface
• ipv6
• install

This installs IPv6 under Windows XP. It is also possible to install the protocol under the network settings options of the Control Panel. Right-click on the appropriate network adapter and select Preferences from the selection. Now select Install on the screen and then Protocol from the available options. Locate Microsoft TCP/IP Version 6, a click on OK installs the selected protocol.

1. Open Network Connections
2. Right-click any local area connection, and then click Properties.
3. Click Install.
4. In the Select Network Component Type dialog box, click Protocol, and then click Add.
5. In the Select Network Protocol dialog box, click Microsoft TCP/IP version 6, and then click OK.
6. Click Close to save changes to your network connection.

You can check again with the ipconfig command to make sure that the IPv6 protocol was installed successfully on the operating system.

Users naturally feel safer using that mode, but that should not be the case. Why? Because there are means to find out which sites have been accessed in private browsing mode.

You see, one feature of the Windows operating system is a DNS cache, that stores domain name and IP links. Without going into to much details, the DNS cache records information about every website that the user opens in a web browser in Windows.

Curious Windows users just need to list the contents of the DNS cache to find out what websites a user has been visiting in private browsing mode. It may require some additional comparisons to find the private browsing mode websites, but that requires just some manual work and can be neglected.

Here is how you can display the contents of the DNS cache:

• Open a command prompt in Windows. The easiest way to do that is to press Windows-R, type cmd and the enter key.
• Now type the command ipconfig /displaydns in the command prompt and hit enter.
• This displays all websites that have been stored in the DNS cache. Please note that this includes everything, which means websites in all web browsers, regardless of whether they have been opened automatically (e.g. by a script on the site) or manually by the user.

Chance is the list is to large for the command line cache. You can use the command ipconfig /displaydns > dns.txt to save the output in the text document dns.txt. It is then possible to open the document in a text editor, to see all records. Opening it in a text editor has other advantages, like being able to search through the records.

Windows offers an option to flush the DNS cache so that all records are deleted from the cache. This is done with the command ipconfig /flushdns.

Some programs (like CCleaner) offer options to delete the DNS Cache. It is also possible to write a simple batch file to delete it on shutdown. Let me know if you like an example script that does that.

Windows users who regularly work in private browsing mode should consider clearing their system’s DNS cache frequently to protect their privacy.

Win IP Config is a program for Windows that makes some of these tools available in a graphical user interface. The interface uses tabs to divide the information and functionality, available are the tabs host info, IP info, interfaces, routes (filtered), netstat and report.

Win IP Config will for instance display in depth information about the network adapters including their gateway, IP, DHCP (DHCP server and lease time) or DNS.

The networking software will also display the current routes and an output of the netstat command in its tabs. Those information alone are valuable and quickly accessible.

Win IP Config provides access to controls in the header as well. Those can be used for instance to renew the IP address or add a new one, to add or delete routes or to display detailed IP statistics including header and address errors plus other problems related to that.

The report tab basically displays all the collected information in an easily readable format. It is possible to export the report as a text document for further processing.

Win IP Config is a handy program for users who prefer to work with a graphical user interface instead of the command line. It does not totally replace the command line as it does not provide access to commands like traceroute or ping.

The program can be downloaded from the developers website. It has not been updated in a while but worked without complications on our 64-bit Windows 7 Professional test system. (via 4Sysops)

Users who try to flush the dns cache might receive the error message “Windows IP Configuration Could not flush the DNS Resolver Cache: Function failed during execution” if the DNS Client service is deactivated.

The solution to fix this error message is to enable the DNS Client service again in the Services configuration menu. I’m not sure if it makes that much sense to flush the cache if the DNS Client is disabled as it should mean that Windows is not resolving and storing DNS at all. Experts who might to weight in are encouraged to do so.

You can start the service by typing [Windows R], [services.msc] [enter]. Locate the DNS Client service, right-click it and select properties from the menu.

You need to set the service to manual or automatic before you are able to start the service.