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IT Explained:What is an 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. The Internet Protocol (IP)
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Class | Leading bits | Size of network number bit 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 |
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 - 10.255.255.255172.16.0.0 - 172.31.255.255
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.
IPv6 addresses
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.domain can 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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