IP Address
An IP address (internet
protocol address) is a numerical representation that uniquely
identifies a specific interface on the network.
Addresses in IPv4 are 32-bits long. This allows for a maximum of
4,294,967,296 (232) unique addresses. Addresses in IPv6 are
128-bits, which allows for 3.4 x 1038 (2128) unique
addresses.
The total usable
address pool of both versions is reduced by various reserved addresses and
other considerations.
IP addresses are
binary numbers but are typically expressed in decimal form (IPv4) or
hexadecimal form (IPv6) to make reading and using them easier for humans.
IP stands for Internet Protocol and describes a set of standards and requirements for creating and transmitting data packets, or datagrams, across networks. The Internet Protocol (IP) is part of the Internet layer of the Internet protocol suite. In the OSI model, IP would be considered part of the network layer. IP is traditionally used in conjunction with a higher-level protocol, most notably TCP. The IP standard is governed by RFC 791.
The Internet Protocol (IP)
How IP Works
IP is designed to
work over a dynamic network. This means that IP must work without a central
directory or monitor, and that it cannot rely upon specific links or nodes
existing. IP is a connectionless protocol that is datagram-oriented., so each
packet must contain the source IP address , destination IP address, and other
data in the header to be successfully delivered.
Combined, these
factors make IP an unreliable, best effort delivery protocol. Error correction
is handled by upper level protocols instead. These protocols include TCP, which
is a connection-oriented protocol, and UDP, which is a connectionless protocol.
Most internet
traffic is TCP/IP.
IP Versions
There are two
versions of IP in use today, IPv4 and IPv6. The original IPv4 protocol is still
used today on both the internet, and many corporate networks. However, the IPv4
protocol only allowed for 232 addresses. This, coupled with how
addresses were allocated, led to a situation where there would not be enough
unique addresses for all devices connected to the internet.
IPv6 was developed
by the Internet Engineering Task Force (IETF), and was formalized in 1998. This
upgrade substantially increased the available address space and allowed for 2128 addresses.
In addition, there were changes to improve the efficiency of IP packet headers,
as well as improvements to routing and security.
IPv4 Addresses
IPv4 addresses are actually 32-bit binary numbers, consisting of the two sub addresses (identifiers) mentioned above which, respectively, identify the network and the host to the network, with an imaginary boundary separating the two. An IP address is, as such, generally shown as 4 octets of numbers from 0-255 represented in decimal form instead of binary form.
For example, the address 168.212.226.204 represents the
32-bit binary number 10101000.11010100.11100010.11001100.
The binary number is
important because that will determine which class of network the IP address
belongs to.
An IPv4 address is typically expressed in dotted-decimal notation, with every eight bits (octet) represented by a number from one to 255, each separated by a dot. An example IPv4 address would look like this:
192.168.17.43
IPv4 addresses are
composed of two parts. The first numbers in the address specify the network,
while the latter numbers specify the specific host. A subnet mask specifies
which part of an address is the network part, and which part addresses the
specific host.
A packet with a
destination address that is not on the same network as the source address will
be forwarded, or routed, to the appropriate network. Once on the correct
network, the host part of the address determines which interface the packet
gets delivered to.
Subnet Masks
A single IP address
identifies both a network, and a unique interface on that network. A subnet
mask can also be written in dotted decimal notation and determines where the
network part of an IP address ends, and the host portion of the address begins.
When expressed in
binary, any bit set to one means the corresponding bit in the IP address is
part of the network address. All the bits set to zero mark the corresponding
bits in the IP address as part of the host address.
The bits marking the
subnet mask must be consecutive ones. Most subnet masks start with 255. and
continue on until the network mask ends. A Class C subnet mask would be
255.255.255.0.
IP Address Classes
|
Class
|
Leading
bits |
Size of network
numberbit field |
Size of rest
bit field |
Number
of networks |
Addresses
per network |
Total addresses
in class |
Start address
|
End address
|
|
Class A
|
0
|
8
|
24
|
128 (27)
|
16,777,216 (224)
|
2,147,483,648 (231)
|
0.0.0.0
|
127.255.255.255
|
|
Class B
|
10
|
16
|
16
|
16,384 (214)
|
65,536 (216)
|
1,073,741,824 (230)
|
128.0.0.0
|
191.255.255.255
|
|
Class C
|
110
|
24
|
8
|
2,097,152 (221)
|
256 (28)
|
536,870,912 (229)
|
192.0.0.0
|
223.255.255.255
|
|
Class D (multicast)
|
1110
|
not defined
|
not defined
|
not defined
|
not defined
|
268,435,456 (228)
|
224.0.0.0
|
239.255.255.255
|
|
Class E (reserved)
|
1111
|
not defined
|
not defined
|
not defined
|
not defined
|
268,435,456 (228)
|
240.0.0.0
|
255.255.255.255
|
Before variable length subnet masks allowed networks of any size to be configured, the IPv4 address space was broken into five classes.Before variable length subnet masks allowed networks of any size to be configured, the IPv4 address space was broken into five classes.
Class A
In a Class A
network, the first eight bits, or the first dotted decimal, is the network part
of the address, with the remaining part of the address being the host part of
the address. There are 128 possible Class A networks.
0.0.0.0 to 127.0.0.0
However, any address
that begins with 127. is considered a loopback address.
Example for a Class A IP
address:
2.134.213.2
Class B
In a Class B
network, the first 16 bits are the network part of the address. All Class B
networks have their first bit set to 1 and the second bit set to 0. In dotted
decimal notation, that makes 128.0.0.0 to 191.255.0.0 as Class B networks.
There are 16,384 possible Class B networks.
Example for a Class B IP
address:
135.58.24.17
Class C
In a Class C network,
the first two bits are set to 1, and the third bit is set to 0. That makes the
first 24 bits of the address the network address and the remainder as the host
address. Class C network addresses range from 192.0.0.0 to 223.255.255.0. There
are over 2 million possible Class C networks.
Example for a Class C IP
address:
192.168.178.1
Class D
Class D addresses are used for multicasting applications. Unlike the previous classes, the Class D is not
used for "normal" networking operations. Class D addresses
have their first three bits set to “1” and their fourth bit set to “0”. Class D
addresses are 32-bit network addresses, meaning that all the values within the
range of 224.0.0.0 – 239.255.255.255 are used to uniquely identify multicast
groups. There are no host addresses within the Class D address space, since all
the hosts within a group share the group’s IP address for receiver purposes.
Example for a Class D IP
address:
227.21.6.173
Class E
Class E networks are
defined by having the first four network address bits as 1. That encompasses
addresses from 240.0.0.0 to 255.255.255.255. While this class is reserved, its
usage was never defined. As a result, most network implementations discard these
addresses as illegal or undefined. The exception is 255.255.255.255, which is
used as a broadcast address.
Example for a Class D IP
address:
243.164.89.28
Overview: IP address classes
and bit-wise representations
Class A
0. 0. 0. 0 = 00000000.00000000.00000000.00000000
127.255.255.255 = 01111111.11111111.11111111.11111111
0nnnnnnn.HHHHHHHH.HHHHHHHH.HHHHHHHH
Class B
128. 0. 0. 0 = 10000000.00000000.00000000.00000000
191.255.255.255 = 10111111.11111111.11111111.11111111
10nnnnnn.nnnnnnnn.HHHHHHHH.HHHHHHHH
Class C
192. 0. 0. 0 = 11000000.00000000.00000000.00000000
223.255.255.255 = 11011111.11111111.11111111.11111111
110nnnnn.nnnnnnnn.nnnnnnnn.HHHHHHHH
Class D
224. 0. 0. 0 = 11100000.00000000.00000000.00000000
239.255.255.255 = 11101111.11111111.11111111.11111111
1110XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX
Class E
240. 0. 0. 0 = 11110000.00000000.00000000.00000000
255.255.255.255 = 11111111.11111111.11111111.11111111
1111XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX
Private Addresses
Within the address
space, certain networks are reserved for private networks. Packets from these
networks are not routed across the public internet. This provides a way for private
networks to use internal IP addresses without interfering with other
networks.The private networks are
10.0.0.1 - 10.255.255.255
172.16.0.0 - 172.32.255.255
192.168.0.0 - 192.168.255.255
Special Addresses
Certain IPv4
addresses are set aside for specific uses:
|
127.0.0.0
|
Loopback address (the host’s own interface)
|
|
224.0.0.0
|
IP Multicast
|
|
255.255.255.255
|
Broadcast (sent to all interfaces on network)
|
IPv4 Address Exhaustion
The original IPv4
specification was designed for the DARPA network that would eventually become
the internet. Originally a test network, no one contemplated how many addresses
might be needed in the future. At the time, the 232 addresses (4.3 billion) were
certainly considered sufficient. However, over time, it became apparent that as
currently implemented, the IPv4 address space would not be big enough for a
worldwide internet with numerous connected devices per person. The last
top-level address blocks were allocated in 2011.
To avoid the seemingly reoccurring issue in technology, where a
specification’s limitation seems more than sufficient at the time, but
inevitably becomes too small, the designers of IPv6 created an enormous address
space for IPv6. The address size was increased from 32 bits in IPv4 to 128 bits
in IPv6.
The IPv6 has a theoretical limit of 3.4 x 1038 addresses.
That’s over 340 undecillion addresses, which is reportedly enough addresses
to assign one to every single atom on the surface of the earth.
IPv6 addresses are
represented by eight sets of four hexadecimal digits, and each set of numbers
is separated by a colon. An example IPv6 address would look like this:
2DAB:FFFF:0000:3EAE:01AA:00FF:DD72:2C4A
IPv6 Address
Abbreviation
With IPv6 addresses
being so long, there are conventions to allow for their abbreviation. First,
leading zeros from any one group of numbers may be eliminated. For example,
:0033: can be written as :33:
Second, any
consecutive sections of zeros can be represented by a double colon. This may be
done only once in any address. The number of sections removed using this
abbreviation can be determined as the number required to bring the address back
up to eight sections. For example, 2DAB::DD72:2C4A would need to have five
sections of zeroes added back in place of the double colon.
(2DAB:0000:0000:0000:0000:0000:DD72:2C4A)
The loopback address
0000:0000:0000:0000:0000:0000:0000:0001
may be abbreviated as ::1.
IPv6 Private Addresses
Like in IPv4 certain
address blocks are reserved for private networks. These addresses are not
routed over the public internet. In IPv6, private addresses are called Unique
Local Addresses (ULA). Addresses from the FC00:: /7 block are ignored and not
routed by default.
Name Resolution
In both IPv4 and IPv6, remembering the IP address of every device is not possible, except on the smallest of networks. Name resolution provides a way to lookup an IP address from an easier to use name.
On the internet, name resolution is handled by the Domain Name
System (DNS). With DNS, a name in the format host.domaincan be used in place of the destination’s
IP address. When the connection is initiated, the source host will request the
IP address of the destination host from a DNS server. The DNS server will reply
with the destination’s IP address. This IP address will then be used for all
communications sent to that name.
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