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IPv4 Addressing

Updated: February 13, 2009

Applies To: Windows 7, Windows Server 2008 R2

For Internet Protocol version 4 (IPv4), each TCP/IP host is identified by a logical IP address. The IP address is a Network layer address and has no dependence on the Data-Link layer address (such as a MAC address of a network adapter). A unique IP address is required for each host and network component that communicates using TCP/IP. This address can be assigned manually or by using Dynamic Host Configuration Protocol (DHCP).

Each IP address includes a network ID and a host ID.

  • The network ID (also known as a network address) identifies the systems that are located on the same physical network bounded by IP routers. All systems on the same physical network must have the same network ID. The network ID must be unique to the network.

  • The host ID (also known as a host address) identifies a workstation, server, router, or other TCP/IP host within a network. The host address must be unique to the network ID.

An IP address consists of 32 bits. Instead of expressing IPv4 addresses 32 bits at a time using binary notation (Base2), it is standard practice to segment the 32 bits of an IPv4 address into four 8-bit fields called octets. Each octet is converted to a decimal number (base 10) from 0–255 and separated by a period (a dot). This format is called dotted decimal notation. The following table provides an example of an IP address in binary and dotted decimal formats.

IP address in binary and dotted decimal formats

 

Binary Format Dotted Decimal Notation

11000000 10101000 00000011 00011000

192.168.3.24

For example, the IPv4 address of 11000000101010000000001100011000 is:

  • Segmented into 8-bit blocks: 11000000 10101000 00000011 00011000

  • Each block is converted to decimal: 192 168 3 24

  • The adjacent octets are separated by a period: 192.168.3.24

The notation w.x.y.z is used when referring to a generalized IP address, and is shown the following figure.

IP address

IP Address

The Internet standards define the following types of IPv4 addresses:

  • Unicast. Assigned to a single network interface located on a specific subnet on the network and used for one-to-one communications.

  • Multicast. Assigned to one or more network interfaces located on various subnets on the network and used for one-to-many communications.

  • Broadcast. Assigned to all network interfaces located on a subnet on the network and used for one-to-everyone-on-a-subnet communications.

The IPv4 unicast address identifies an interface’s location on the network in the same way a street address identifies a house on a city block. Just as a street address must identify a unique residence, an IPv4 unicast address must be globally unique to the network and have a uniform format.

Each IPv4 unicast address includes a network ID and a host ID.

  • The network ID (also known as a network address) is the fixed portion of an IPv4 unicast address that identifies the set of interfaces that are located on the same physical or logical network segment as bounded by IPv4 routers. A network segment on TCP/IP networks is also known as a subnet. All systems on the same physical or logical subnet must use the same network ID and the network ID must be unique to the entire TCP/IP network.

  • The host ID (also known as a host address) is the variable portion of an IPv4 unicast address that is used to identify a network node’s interface on a subnet. The host ID must be unique to the network ID.

If the network ID is unique to the TCP/IP network and the host ID is unique to the network ID, then the entire IPv4 unicast address consisting of the network ID and host ID is unique to the entire TCP/IP network.

IPv4 multicast addresses are used for single-packet, one-to-many delivery. On an IPv4 multicast-enabled intranet, an IPv4 packet addressed to an IPv4 multicast address is forwarded by routers to the subnets on which there are hosts listening to the traffic sent to the IPv4 multicast address. IPv4 multicast provides an efficient one-to-many delivery service for many types of communication.

IPv4 multicast addresses are defined by the class D Internet address class: 224.0.0.0/4. IPv4 multicast addresses range from 224.0.0.0 through 239.255.255.255. IPv4 multicast addresses for the 224.0.0.0/24 address prefix (224.0.0.0 through 224.0.0.255) are reserved for local subnet multicast traffic.

IPv4 uses a set of broadcast addresses to provide a one-to-everyone-on-the-subnet delivery service. Packets sent to IPv4 broadcast addresses are processed by all the interfaces on the subnet. The following are the different types of IPv4 broadcast addresses:

  • Network broadcast. Formed by setting all the host bits to 1 for a classful address prefix. An example of a network broadcast address for the classful network ID 131.107.0.0/16 is 131.107.255.255. Network broadcasts are used to send packets to all interfaces of a classful network. IPv4 routers do not forward network broadcast packets.

  • Subnet broadcast. Formed by setting all the host bits to 1 for a classless address prefix. An example of a network broadcast address for the classless network ID 131.107.26.0/24 is 131.107.26.255. Subnet broadcasts are used to send packets to all hosts of a classless network. IPv4 routers do not forward subnet broadcast packets. For a classful address prefix, there is no subnet broadcast address, only a network broadcast address. For a classless address prefix, there is no network broadcast address, only a subnet broadcast address.

  • All-subnets-directed broadcast. Formed by setting all the original classful network ID host bits to 1 for a classless address prefix. A packet addressed to the all-subnets-directed broadcast was defined to reach all hosts on all of the subnets of a subnetted class-based network ID. An example of an all-subnets-directed broadcast address for the subnetted network ID 131.107.26.0/24 is 131.107.255.255. The all-subnets-directed broadcast is the network broadcast address of the original classful network ID. IPv4 routers can forward all-subnets-directed broadcast packets, but the use of the all-subnets-directed broadcast address is deprecated in RFC 1812.

  • Limited broadcast. Formed by setting all 32 bits of the IPv4 address to 1 (255.255.255.255). The limited broadcast address is used for one-to-everyone delivery on the local subnet when the local network ID is unknown. IPv4 nodes typically only use the limited broadcast address during an automated configuration process such as Bootstrap Protocol (BOOTP) or DHCP. For example, with DHCP, a DHCP client must use the limited broadcast address for all traffic sent until the DHCP server acknowledges the use of the offered IPv4 address configuration. IPv4 routers do not forward limited broadcast packets.

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