IP
Addressing:
In computer
networking, an IP address (internet protocol address) is a unique number that
devices use in order to identify and communicate to each other on a network
utilizing the Internet Protocol standard. IP addresses (more accurately, Ipv4
addresses) are 32 bit integers, usually represented in the familiar dot-based
notation. The dot-based notation is a decimal representation for each byte of
IP address. For example, an IP address with a hex value of 0x800A080B is
represented as 128.10.8.11.
Any participating
device including routers, computers, time-servers, printers, Internet fax
machines, and nowadays Internet telephones must have its own globally unique
communicable address.
Since IP
addresses are not easy to remember, the domain name system provides the ability
to map domain name (e.g. indianrail.gov.in) to an IP address (203.197.236.135).IPv4
uses 32-bit (4 byte) addresses, which limits the address space to about 4.2
billion possible unique addresses. However, many are reserved for special
purpose such as private networks (about 18 million addresses). This reduces the
number of addresses that can be allocated as public internet addresses and as
the number of addresses available is consumed, an IPv4 address shortage appears
to be inevitable in the long run.
The internet
as the name suggests, is a network of networks. Thus to uniquely identify a
host on the internet, one needs to know the network’s id and the host id in the
network. Thus an IP address consist of two components 1) Network ID and 2) Host
ID. The network id is the number assigned to a network in the internet. Host id
represents the id assigned to a host in the network.
IP Address
Classification:
The most
familiar example of a single address actually having different addresses for
network and host is telephone number. For example, telephone number of Matrix Educare
is 2530.9378. First four digits 2530, identifies a BSNL exchange and the next
four digits identifies the particular telephone in the exchange. In IP
addresses, the assignment of bits to network id and the host id depends upon
the “class” of the address.
Class A:
IP address
is suitable when the Internet consists of a small number of networks but each
network is consists of large number of hosts. The m.s.b (i.e., bit 31) of the
address is 0 and the next 7 bits represent the network address, leaving 24 bits
to address a host in the network. The range of class A addresses is from
1.0.0.0 to 127.255.255.255.
Class B:
IP addresses
allow for 16, 382 networks each having up to 65,536 hosts. The two most significant
bits of class B IP address are 1 and 0. Addresses range from 128.0.0.0 till
191.255.255.255.
Class C:
IP addresses
allow for 2 million networks each having up to 254 hosts. The three most significant
bits of class C IP address are 1, 1 and 0.
Class D:
IP addresses
with four most significant bits as 1110, called Class D. IP addresses are
reserved for multicast addresses. They range from 224.0.0.0 to 239.255.255.255.
Class E:
IP addresses with five most significant bits
as 11110, sometimes called class E IP address are reserved for future use.
The address
127.0.0.1 Network id is left out because it is designated for loop-back and
cannot be assigned to a network.
Special IP Addresses:
A few IP Addresses has special meanings:
- The address 0.0.0.0 (i.e. all 0-s in binary) always means “this
host”.
- If the higher 12 bits are all 0-s then it means a host on
this network where the host id is given by the lower 20 bits.
- The address 255.255.255.255 (i.e., all 1-s in binary) is
reserved for broadcast on this network.
- Any address 127.X.X.X (X can be anything) is a loopback
address.
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