Both protocol versions are used in the Internet, and a
slow migration toward IPv6 is in progress.
The main role of IP is to uniquely identify devices at the
Internet layer in the TCP/IP reference model and Layer 3
in the OSI model. IPv4 uses 32-bit addresses, which
means it can theoretically support 2 (just over 4
billion) unique addresses. It is a connectionless protocol,
IP data packets are forwarded individually, the delivery
of packets is best effort, and there is no retransmission or
data recovery functionality specified in the protocol
definition. In case of lost or corrupt packets,
retransmission and data recovery are left to be
implemented by the higher-layer protocols. Since the
physical medium and transmission are handled by the
data link layer, all those specifications are abstracted
from the Internet layer, and IP operates independently of
the medium that is carrying the data.
IP addresses are similar to physical addresses of homes
and businesses. The same way the address of a house
uniquely identifies it so that packages and other mail can
be delivered, the IP address uniquely identifies all the
devices connected to the Internet so that data packages
can be exchanged and delivered. For easier readability
for humans, IPv4 addresses are split into four octets,
with each decimal value separated by a dot—in a format
known as dotted decimal notation. Each octet is made up
of 8 bits, and each bit can have a value of 1 or 0. For
example, an IP address would take the following form in
the IP header: 11000000101010000011000001000001.
It is very easy to make mistakes when representing IP
addresses this way. The four-octet dotted decimal
notation for the same address becomes 192.168.48.65,
which is much easier to remember and keep track of.
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