Troubleshooting IP Configuration

Windows 7 retains the same command-line tools of its predecessors for troubleshooting IP configurations. The most basic tools are the Ping and Ipconfig utilities which help you determine your system’s IP configuration and test connectivity. There are more advanced network tools such as, Tracert or Pathping, Nslookup for DNS related issues, etc.  These help you troubleshoot advanced network related issues but this article will only cover the basic command-line tools which are adequate for the Windows 7 average users.

The Ping command-line tool is in general used to test the network connectivity of a computer by sending a message to a target computer while it expects a reply! The Ping also measures the time the message takes to hit the other computer and returns back which is known as the round-trip time. Technically, Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to a target computer and waiting for an ICMP response. In the process it measures the time from transmission to reception (round-trip time) but most importantly it records packet losses when there are problems with the connection.

As most modern Internet devices such as, routers, firewalls and hosts block this protocol as a preventive measure against denial of service attacks, you can still use the tool to test if your IP protocol is working fine by typing the command ping 127.0.0.1 or ping ‘your computer IP address’ from a command prompt. If you can ping your computer’s IP address then you can try to ping another computer’s or the default gateway’s IP address. If your network has an internal DNS server or has ICS or WAP configured then you can ping computers by their host names such as, ping computer1.  Remember, that IPv6 can resolve your own computer name when no DNS services are implemented in your network. A good practice when troubleshooting IP configuration is to use the ping command with the -t option. Since, the default behavior of the tool is to perform just three pings to a target IP address, with the -t option (ex: ping computer1 -t) it runs for ever and hence, you can monitor the connectivity or configuration during troubleshooting tasks. To stop the ping output then press Ctrl+c. To see the full list of the ping command options, type ping /? from a command prompt.

You can also use the Ipconfig tool for troubleshooting. In fact, you can gather all the information you need by typing ipconfig /all from a command prompt before starting troubleshooting. Viewing your system IP configuration from the ipconfig /all command output, helps you determine whether your computer is obtaining its IP address from DHCP services correctly and completely such as, gateway and DNS server IP addresses. For instance, if you find that your computer is getting an APIPA IP address (169.254.0.1 to 169.254.255.254) then it may indicate that you have a connection problem if you’re supposed to get an IP address from a DHCP server. Using the IP addresses of the default gateway and DNS server listed in the ipconfig /all output, you can then use the ping command tool to test your connectivity to these hosts.  Remember, that the ping packets may not reach a host if the host’s has a firewall rule set to block ICMP packets (ping).

Ipconfig is also useful when refreshing your system’s IP configuration. The command options /release and /renew allows you to release the old configuration and obtain a new one. Although, the ipconfig /renew command should be enough to release and obtain a new IP configuration in one step, many times this fails and you end up using ipconfig /release to just release your configuration and then obtain a new one using the ipconfig /renew command. Obtaining a new IP configuration may not register your computer with the DNS servers immediately and hence, you may need to execute ipconfig /registerdns so that your new configuration is registered right away. While troubleshooting IP configurations you may change a couple of settings that may remain stored in the computer’s cache. Computers cache DNS names for some time as to speed up the resolution process. However, the cached information may be incorrect due to some modifications done during troubleshooting. Therefore, with every change you make rather than waiting for the cached information to expire, type the ipconfig /flushdns command to flush the DNS cache. To see the full list of the ipconfig command options, type ipconfig /? from an elevated command prompt.

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