IP Addressing

It is a numeric identifier assigned to each machine on an IP network. It designates the specific location of a device on the network. An IP address is a software address, not a hardware address—the latter is hard-coded on a network interface card (NIC) and used for finding hosts on a local network. IP addressing was designed to allow hosts on one network to communicate with a host on a different network.

IP Terminology

Bit A bit is one digit, either a 1 or a 0.
Byte A byte is 7 or 8 bits, depending on whether parity is used.
Octet An octet, made up of 8 bits, is just an ordinary 8-bit binary number.
Network address This is the designation used in routing to send packets to a remote network.
Broadcast address The address used by applications and hosts to send information to all nodes on a network is called the broadcast address.

The Hierarchical IP Addressing Scheme

An IP address consists of 32 bits of information. These bits are divided into four sections, referred to as octets or bytes, each containing 1 byte (8 bits). You can depict an IP address using one of three methods: Dotted-decimal,

Class A: Network . Host . Host . Host
Class B: Network . Network . Host . Host
Class C: Network . Network . Network . Host
Class D: Multicast
Class E: Research
  • Network Address Range: Class A

    The designers of the IP address scheme said that the first bit of the first byte in a Class A network address must always be off, or 0. This means a Class A address must be between 0 and 127 in the first byte, inclusive.
  • Network Address Range: Class B

    Class B network is defined when the first byte is configured from 128 to 191.
  • Network Address Range: Class C

    An IP address that starts at 192 and goes to 223,
  • Network Address Ranges: Classes D and E

    The addresses between 224 to 255 are reserved for Class D and E networks. Class D (224–239) is used for multicast addresses and Class E (240–255) for scientific purposes,
  • Network Addresses: Special Purpose

    Some IP addresses are reserved for special purposes, so network administrators can’t ever assign these addresses to nodes.

Address Function

Network Reserved for loopback tests. Designates the local node and allows that node to send a test packet to itself without generating network traffic.

Node address of all 0s Interpreted to mean “network address” or any hoston specified network.

Node address of all 1s Interpreted to mean “all nodes” on the specified network; for example, means “all nodes” on network 128.2 (Class B address).

Entire IP address set to all 0s Used by Cisco routers to designate the default route. Could also mean “any network.” Entire IP address set to all 1s (same as Broadcast to all nodes on the current network; sometimes called an “all 1s broadcast” or limited broadcast.

Private IP Addresses

The people who created the IP addressing scheme also created what we call private IP addresses. These addresses can be used on a private network, but they’re not routable through the Internet.

This is designed for the purpose of creating a measure of well-needed security, but it also conveniently saves valuable IP address space. If every host on every network had to have real routable IP addresses, we would have run out of IP addresses to hand out years ago. But by using private IP addresses, ISPs, corporations, and home users only need a relatively tiny group of bona fide IP addresses to connect their networks to the Internet. This is economical because they can use private IP addresses on their inside networks and get along just fine.

To accomplish this task, the ISP and the corporation—the end user, no matter who they are—need to use something called Network Address Translation (NAT)

Address Class Reserved Address Space

Class A 10 . 0 . 0 . 0  through 10 . 255 . 255 . 255

Class B 172 . 16 . 0 . 0  through 172 . 31 . 255 . 255

Class C 192 . 168 . 0 . 0 through 192 . 168 . 255 . 255

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