Windows IP Configuration Tool (ipconfig)
The Windows IP Configuration tool (ipconfig) is the command-line equivalent of the accessory "Winipcfg" that was present in Windows 9X/Me. It is used to display the TCP/IP network configuration values. To open it, enter "ipconfig" in the command prompt. If you are connected directly to the Internet, you will obtain your IP address. (For a discussion of what an IP is, go here.) The figure below shows the result for a broadband connection where the IP is assigned automatically. Here the IP is your computer's temporary address on the Internet.
If you are on a local area network using a router, the information is different. You do not obtain the IP corresponding to the network's address on the Internet. (To obtain the IP that the Internet sees, go to a source such as
DSL Reports Whois.) The IP given is the
local address on the network. This information can be helpful in diagnosing network problems. Also listed is the "gateway" or router address on the local network. The figure below illustrates the result.
Switches for IPConfig
There are also a variety of switches for
ipconfig that add functions. These are invoked by entering "ipconfig /{
switch}". To obtain a list of switches, enter "ipconfig /?" or "ipconfig -?". These are shown in the figure below. The switches of most interest to everyday use are "
release" and "
renew". Note that IP addresses are typically assigned or "leased" for a period of time, often a day or more. It sometimes happens that IP addresses are no longer valid or are in conflict. Problems can often be solved by first releasing the IP address and then renewing it. Sometimes cable or DSL modems that seem to be disabled can be restored this way. If you travel and use broadband connections elsewhere, you will often find this procedure of releasing and renewing the IP address to be necessary.
For a detailed output of network parameters, you can use the command "ipconfig /all". Unless you are experienced with networks, however, this may be more than you want to know.
The switches "flushdns" and "displaydns" are are also sometimes useful in everyday use and they are discussed on
another page at a sister site.
Ping
Ping is an old Unix tool that has been around for a long time but many PC users are unfamiliar with the Windows version.
Ping sends out a packet to a designated internet host or network computer and measures its response time. The target computer will return (hopefully) a signal. It is a way of determining the quality of your connection to another site. You will also receive an IP address that corresponds to the user-friendly type of URL (see
this page for further discussion of IPs and URLs). To use ping, open a command window (or DOS in Windows 9X/Me) and type: ping <hostname>. For example, to ping Dell enter: ping dell.com Please note the use of a hostname, not a complete URL. The prefix "http://" is never used. Many sites also do not require "www" . By convention, 32 byte packets will be transmitted four times. You will receive a screen output that looks like:
The screen tells me that the IP for
dell.com is 143.166.83.230 (For the moment, at least. This can change.) It also tells me that the average round trip time for a packet was 69 milliseconds, which means I have a good connection to
dell.com. Long reply times of several hundred milliseconds are indicative of a slow connection. Note that some major sites such as
microsoft.com do not like being pinged and block pings. In that case you will get a "Request timed out" message.
In addition to being used on the Internet, Ping is often used to test connections on local networks. More details can be found in this
Microsoft article.
Tracert
Tracert (traceroute) is another old tool borrowed from Unix. The actual path between two computers on the Internet is not a straight line but consists of numerous segments or "hops" from one intermediate computer to another. Tracert shows each step of the path taken. It can be interesting to see just how convoluted it is. The times for each hop and the IP addresses for each intermediate computer are displayed. Tracert shows up to 30 hops. It is convenient for finding if there is one particular segment that is causing a slow or bad connection. A typical command might be "tracert dell.com".
Pathping
This command combines functions of Ping and Tracert. Pathping will first list the number of hops required to reach the address you are testing and then send multiple pings to each router between you and the destination. After that, it computes results based on the packets returned from each router. Because pathping displays the degree of packet loss at any given router or link, you can determine which routers or subnets might be having network problems. Note that the whole process may consume 5-10 minutes because many pings are being sent. There are switches to modify the process and these can be seen by entering "pathping /?" in the command prompt.
Netstat
Netstat displays the active TCP connections and ports on which the computer is listening, Ethernet statistics, the IP routing table, statistics for the IP, ICMP, TCP, and UDP protocols. It comes with a number of switches for displaying a variety of properties of the network and TCP connections.
(One tricky point: the switches must be prefixed with a minus, not a slash.) More detail is
at this page. One possible use for
Netstat is to determine if spyware or Trojans have established connections that you do not know about. The command "netstat -a" will display all your connections. The command "netstat -b" will show the executable files involved in creating a connection. A figure showing all the switches and syntax is given below.
Nslookup
This command helps diagnose the Domain Name System (DNS) infrastructure and comes with a number of sub-commands. These are mainly for systems administrators. The primary interest for average PC users is its use to find the computer name corresponding to a numeric IP. For example, if you want to know who is "216.109.112.135" , enter "nslookup 216.109.112.135" and you will find that it is (or was anyway) a Yahoo computer. My firewall keeps a log of the IPs involved in the attempts to probe my computer and I sometimes look a few up to see who they are. (There are also Whois search sites available on the Web as mentioned in the Ipconfig section.)
Netsh
The network services shell is a large suite of many tools. I discuss it in some depth on
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