IP scanner PRTG – IP check, traffic & PING

IPv4 addresses are actually 32-bit binary numbers, consisting of the two subaddresses (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

Before variable length subnet masks (introduced with RFC-1519 in 1993) allowed networks of almost any size to be configured regardless of the actual address, the IPv4 address space was broken into five classes as follows:

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 - 10.255.255.255

172.16.0.0 - 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.