Command Reference for IPCONFIG MS-DOS

Ipconfig is a MS-DOS command-line tool used to display and manage the network settings of your computer. Ipconfig is available on Windows machines, and it displays the current network connection details and dhcp client settings.

Ipconfig is an external MS-DOS command, and is available on Windows 95, Windows 98, ME, NT, 2000, XP and Windows Vista Operating Systems. On Windows 9x machines, a graphical tools such as "winipconfig" or "winipcfg" may be used instead. On Linux machine, the if configcommand performs equivalent function.

C:\> ipconfig /?

USAGE:
    ipconfig [/? | /all | /renew [adapter] | /release [adapter] |
              /flushdns | /displaydns | /registerdns |
              /showclassid adapter |
              /setclassid adapter [classid] ]

where
    adapter         Connection name
                   (wildcard characters * and ? allowed, see examples)

    Options:
       /?           Display this help message
       /all         Display full configuration information.
       /release     Release the IP address for the specified adapter.
       /renew       Renew the IP address for the specified adapter.
       /flushdns    Purges the DNS Resolver cache.
       /registerdns Refreshes all DHCP leases and re-registers DNS names
       /displaydns  Display the contents of the DNS Resolver Cache.
       /showclassid Displays all the dhcp class IDs allowed for adapter.
       /setclassid  Modifies the dhcp class id.

The default is to display only the IP address, subnet mask and
default gateway for each adapter bound to TCP/IP.

For Release and Renew, if no adapter name is specified, then the IP address
leases for all adapters bound to TCP/IP will be released or renewed.

For Setclassid, if no ClassId is specified, then the ClassId is removed.

Examples:
    > ipconfig                   ... Show information.
    > ipconfig /all              ... Show detailed information
    > ipconfig /renew            ... renew all adapters
    > ipconfig /renew EL*        ... renew any connection that has its
                                     name starting with EL
    > ipconfig /release *Con*    ... release all matching connections,
                                     eg. "Local Area Connection 1" or
                                         "Local Area Connection 2"

C:\>ipconfig /all

Windows IP Configuration

        Host Name . . . . . . . . . . . . : topwebhosts
        Primary Dns Suffix  . . . . . . . :
        Node Type . . . . . . . . . . . . : Hybrid
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Wireless Network Connection:

        Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : Intel(R) PRO/Wireless LAN 2100 3B Mi
ni PCI Adapter
        Physical Address. . . . . . . . . : 00-0C-F1-65-5B-70
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 192.168.1.1
        Lease Obtained. . . . . . . . . . : Thursday, February 08, 2007 2:27:17
PM
        Lease Expires . . . . . . . . . . : Thursday, February 15, 2007 2:27:17
PM

Ethernet adapter Local Area Connection:

        Media State . . . . . . . . . . . : Media disconnected
        Description . . . . . . . . . . . : Intel(R) PRO/1000 MT Mobile Connecti
on
        Physical Address. . . . . . . . . : 00-0D-60-FB-4E-E9

To learn the names of ethernet adapters that you can optionally specify with "ipconfig" command, you may simply type ipconfig command by itself. The command output displays all adapters by name that are available on your computer: e.g. "Local Area Connection", "Wireless Network Connection".

Ipconfig command is most often used to diagnose network problem on a Windows machine. If you're using DHCP, you may try releasing and renewing IP address by performing "ipconfig /release" and "ipconfig /renew" commands shown below.

C:\> ipconfig /release
Windows IP Configuration

No operation can be performed on Local Area Connection while it has its media di
sconnected.

Ethernet adapter Wireless Network Connection:

        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 0.0.0.0
        Subnet Mask . . . . . . . . . . . : 0.0.0.0
        Default Gateway . . . . . . . . . :

Ethernet adapter Local Area Connection:

        Media State . . . . . . . . . . . : Media disconnected

C:\> ipconfig /renew

Windows IP Configuration

Ethernet adapter Wireless Network Connection:

        Connection-specific DNS Suffix  . :
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1

To workaround DNS caching issue, you may perform "ipconfig /flushdns" to clear DNS cache value on your computer. DNS uses TTL (Time-To-Live) value which let the intermediate name servers to cache DNS information. If you changed your DNS settings, and your computer doesn't see the change immediately, you may perform "ipconfig /flushdns" to clear the DNS cache.

C:\> ipconfig /flushdns

Windows IP Configuration

Successfully flushed the DNS Resolver Cache.

IP Address

Internet Protocol Address (or IP Address) is an unique address that computing devices use to identify itself and communicate with other devices in the Internet Protocol network. Any device connected to the IP network must have an unique IP address within its network. An IP address is analogous to a street address or telephone number in that it is used to uniquely identify a network device to deliver mail message, or call ("view") a website.

Dotted Decimals

The traditional IP Addresses (IPv4) uses a 32-bit number to represent an IP address, and it defines both network and host address. Due to IPv4 addresses running out, a new version of the IP protocol (IPv6) has been invented to offer virtually limitless number of unique addresses. An IP address is written in "dotted decimal" notation, which is 4 sets of numbers separated by period each set representing 8-bit number ranging from (0-255). An example of IPv4 address is 216.3.128.12, which is the IP address assigned to topwebhosts.org.

An IPv4 address is divided into two parts: network and host address. The network address determines how many of the 32 bits are used for the network address, and remaining bits for the host address. The host address can further divided into subnetwork and host number.

Class A, B, C and CIDR networks

Traditionally IP network is classified as A, B or C network. The computers identified the class by the first 3 bits (A=000, B=100, C=110), while humans identify the class by first octet(8-bit) number. With scarcity of IP addresses, the class-based system has been replaced by Classless Inter-DomainRouting (CIDR) to more efficiently allocate IP addresses.

Class	Network Address	Number of Hosts	Netmask
CIDR	/4	240,435,456	240.0.0.0
CIDR	/5	134,217,728	248.0.0.0
CIDR	/6	67,108,864	252.0.0.0
CIDR	/7	33,554,432	254.0.0.0
A	/8 (1-126)	16,777,216	255.0.0.0
CIDR	/9	8,388,608	255.128.0.0
CIDR	/10	4,194,304	255.192.0.0
CIDR	/11	2,097,152	255.224.0.0
CIDR	/12	1,048,576	255.240.0.0
CIDR	/13	524,288	255.248.0.0
CIDR	/14	262,144	255.252.0.0
CIDR	/15	131,072	255.254.0.0
B	/16 (128-191)	65,534	255.255.0.0
CIDR	/17	32,768	255.255.128.0
CIDR	/18	16,384	255.255.192.0
CIDR	/19	8,192	255.255.224.0
CIDR	/20	4,096	255.255.240.0
CIDR	/21	2,048	255.255.248.0
CIDR	/22	1,024	255.255.252.0
CIDR	/23	512	255.255.254.0
C	/24 (192-223)	256	255.255.255.0
CIDR	/25	128	255.255.255.128
CIDR	/26	64	255.255.255.192
CIDR	/27	32	255.255.255.224
CIDR	/28	16	255.255.255.240
CIDR	/29	8	255.255.255.248
CIDR	/30	4	255.255.255.252

Note: (1) 127 Network Address reserved for loopback test. (2) Class D (224-247, Multicast) and Class E (248-255, Experimental) are not intended to be used in public operation. 

Public and Private IP Addresses 

In order to maintain uniqueness within global namespace, the IP addresses are publicly registered with the Network Information Center (NIC) to avoid address conflicts. Devices that need to be publicly identified such as web or mail servers must have a globally unique IP address, and they are assigned a public IP address. Devices that do not require public access may be assigned a private IP address, and make it uniquely identifiable within one organization. For example, a network printer may be assigned a private IP address to prevent the world from printing from it. To allow organizations to freely assign private IP addresses, the NIC has reserved certain address blocks for private use. A private network is a network that uses RFC 1918 IP address space. The following IP blocks are reserved for private IP addresses.

Class	Starting IP Address	Ending IP Address
A	10.0.0.0	10.255.255.255
B	172.16.0.0	172.31.255.255
C	192.168.0.0	192.168.255.255

In addition to above classful private addresses, 169.254.0.0 through 169.254.255.255 addresses are reserved for Zeroconf (or APIPA, Automatic Private IP Addressing) to automatically create the usable IP network without configuration.

What is loopback IP address? 

The loopback IP address is the address used to access itself. The IPv4 designated 127.0.0.1 as the loopback address with the 255.0.0.0 subnet mask. A loopback interface is also known as a virtual IP, which does not associate with hardware interface. On Linux systems, the loopback interface is commonly called lo or lo0. The corresponding hostname for this interface is called localhost.

The loopback address is used to test network software without physically installing a NetworkInterface Card (NIC), and without having to physically connect the machine to a TCP/IP network. A good example of this is to access the web server running on itself by using http://127.0.0.1 or http://localhost.