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IP Addressing
IP (Internet Protocol) address is a unique identifier for the node or host connection on an IP network. It is a 32 bit binary number represented as 4 decimal values, where each value representing 8 bits in the range of 0 to 255, separated by decimal points. This is called as “dotted decimal” notation.
For example, 140.179.220.200 in binary format it can be written as 10001100.10110011.11011100.11001000
Every IP address consists of two parts, one for identifying the network and one for identifying the node. The subnet mask and the class of the address determines which part belongs to the network address and which part belongs to the node address.
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Address Classes:
There are five different address classes which can determine the class by examining the first 4 bits of an IP address. They are:
Class A addresses begin with 0xxx, or 1 to 126 decimal.
Class B addresses begin with 10xx, or 128 to 191 decimal.
Class C addresses begin with 110x, or 192 to 223 decimal.
Class D addresses begin with 1110, or 224 to 239 decimal.
Class E addresses begin with 1111, or 240 to 254 decimal.
For loopback and for internal testing on a local machine, addresses that are beginning with 01111111, or 127 decimal, are reserved.
For example, you can test that you should always be able to ping 127.0.0.1, which is pointed to yourself.
Similarly, Class D addresses are reserved for multicasting and Class E addresses are reserved for the future use. And they should not be used for host addresses.
The Class determines as follows, by default, IP address belongs to the network (caps N) and the part that belongs to the node (small n).
Class A — NNNNNNNN.nnnnnnnn.nnnnnnnn.nnnnnnnn
Class B — NNNNNNNN.NNNNNNNN.nnnnnnnn.nnnnnnnn
Class C – NNNNNNNN.NNNNNNNN.NNNNNNNN.nnnnnnnn
For example, 140.179.220.200 is a Class B address. So, by default, the network part (Network Address) is the first two octets (140.179.x.x) and the node part is the last 2 octets (x.x.220.200).
For specifying the network address for a given IP address, the node section is set to all “0”s.
For example, 140.179.0.0 will specify the network address for IP address 140.179.220.200.
If the node section is set to all “1”s, it specifies a broadcast that is sent to all the hosts on the network.
And 140.179.255.255 will be specified as an example broadcast address and this will be true regardless of the length of the node section.
Private Subnets:
For private networks, there are three IP network addresses. They are 10.0.0.0, Subnet Mask 255.0.0.0, 172.16.0.0, Subnet Mask 255.240.0.0 and 192.168.0.0, Subnet Mask 255.255.0.0.
These addresses can also be notated as 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
These can be used by anyone by setting up the internal IP networks, like lab or home LAN behind a NAT or proxy server or a router. Using these is always safe because the routers on the Internet will never forward packets coming from these addresses by default.
Subnetting
Subnetting an IP Network can be done for various reasons, including organization, use of different types of physical media like Ethernet, FDDI, WAN etc., preservation of address space, and security. But the most common reason is to control the network traffic. In an Ethernet network, all the nodes on a segment can see all the packets that are transmitted by all other nodes on that segment. Due to heavy traffic loads or due to collisions and the resulting retransmissions, the performance will be affected. To reduce the amount of traffic that each segment must receive, a router can be used to connect IP networks.
Subnet Masking:
To identify the network and the node parts of the address, we can apply the subnet mask to an IP address. In the mask, the network bits are represented by 1s, and the node bits are represented by 0s. The Network Address or Number can be obtained by performing a bitwise logical AND operation between the IP address and the subnet mask.
For example, by using our test IP address and the default Class B subnet mask, gives
10000011.10110011.11110000.11001000 140.179.240.200 Class B IP Address
11111111.11111111.00000000.00000000 255.255.000.000 Default Class B Subnet Mask
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10001100.10110011.00000000.00000000 140.179.000.000 Network Address
Default subnet masks:
Class A – 255.0.0.0 – 11111111.00000000.00000000.00000000
Class B – 255.255.0.0 – 11111111.1111111.00000000.0000000
Class C – 255.255.255.0 – 11111111.11111111.11111111.00000000