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.
|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 127.0.0.1 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, 184.108.40.206 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; 255.255.255.255) 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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