Introduction
It will cover the basics of IP
addressing and subnetting.
- What is an IP Address?
- What are Classes?
- What is a Network Address?
- What are Subnet Masks and Subnet Addresses?
- How are Subnet Masks defined and used?
- How can all this be applied?
- What is CIDR?
- How can I get more information?
An IP (Internet Protocol) address is a
unique identifier for a node or host connection on an IP network. An
IP address is a 32 bit binary number usually represented as 4 decimal
values, each representing 8 bits, in the range 0 to 255 (known as
octets) separated by decimal points. This is known as "dotted
decimal" notation.
Example: 115.113.194.2
IP Addressing
Every IP address consists of two parts, one identifying the
network and one identifying the node. The Class of the address and
the subnet mask determine which part belongs to the network address
and which part belongs to the node address.
Address Classes
There are 5 different address classes. You can determine which
class any IP address is in by examining the first 4 bits of the IP
address.
Class
|
Start address
|
Finish address
|
A
|
0.0.0.0
|
126.255.255.255
|
B
|
128.0.0.0
|
191.255.255.255
|
C
|
192.0.0.0
|
223.255.255.255
|
D
|
224.0.0.0
|
239.255.255.255
|
E
|
240.0.0.0
|
255.255.255.255
|
IP address Classes
Addresses beginning with 01111111, or 127 decimal,
are reserved for loopback and for internal testing on a local
machine; [You can test this: you should always be able to ping
127.0.0.1, which points to yourself] Class D addresses are
reserved for multicasting; Class E addresses are reserved for future
use. They should not be used for host addresses.
In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 1115.113.0.0 specifies the network address for 115.113.220.200. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 115.113.255.255 specifies the example broadcast address. Note that this is true regardless of the length of the node section.
Private Subnets
There are three IP network addresses reserved for private
networks. The addresses 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 are also notated
10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16;
this notation will be explained later in this tutorial. They can be
used by anyone setting up internal IP networks, such as a lab or home
LAN behind a NAT or proxy server or a router. It is always safe to
use these because routers on the Internet by default will never
forward packets coming from these addresses.
Subnetting
Subnet Masking
Subnetting
Subnet Masking
Applying a subnet mask to an IP address allows you to identify the
network and node parts of the address. The network bits are
represented by the 1s in the mask, and
the node bits are represented by the 0s.
Performing a bitwise logical
AND operation between the IP address and the
subnet mask results in the Network Address or Number.
Default subnet masks:
- Class A - 255.0.0.0 - 11111111.00000000.00000000.00000000
- Class B - 255.255.0.0 - 11111111.11111111.00000000.00000000
- Class C - 255.255.255.0
- 11111111.11111111.11111111.00000000
We will break this network into 14 subnets of 14 nodes each. This
will limit us to 196 nodes on the network instead of the 254 we would
have without subnetting, but gives us the advantages of traffic
isolation and security. To accomplish this, we need to use a subnet
mask 4 bits long.
Recall that the default Class C subnet mask is
Recall that the default Class C subnet mask is
255.255.255.0 (11111111.11111111.11111111.00000000 binary)
Extending this by 4 bits yields a mask of
255.255.255.240 (11111111.11111111.11111111.11110000 binary)
This gives us 16 possible network numbers, 2 of which cannot be used:
| Subnet bits | Network Number | Node Addresses | Broadcast Address |
| 0000 | 200.133.175.0 | Reserved | None |
| 0001 | 200.133.175.16 | .17 thru .30 | 200.133.175.31 |
| 0010 | 200.133.175.32 | .33 thru .46 | 200.133.175.47 |
| 0011 | 200.133.175.48 | .49 thru .62 | 200.133.175.63 |
| 0100 | 200.133.175.64 | .65 thru .78 | 200.133.175.79 |
| 0101 | 200.133.175.80 | .81 thru .94 | 200.133.175.95 |
| 0110 | 200.133.175.96 | .97 thru .110 | 200.133.175.111 |
| 0111 | 200.133.175.112 | .113 thru .126 | 200.133.175.127 |
| 1000 | 200.133.175.128 | .129 thru .142 | 200.133.175.143 |
| 1001 | 200.133.175.144 | .145 thru .158 | 200.133.175.159 |
| 1010 | 200.133.175.160 | .161 thru .174 | 200.133.175.175 |
| 1011 | 200.133.175.176 | .177 thru .190 | 200.133.175.191 |
| 1100 | 200.133.175.192 | .193 thru .206 | 200.133.175.207 |
| 1101 | 200.133.175.208 | .209 thru .222 | 200.133.175.223 |
| 1110 | 200.133.175.224 | .225 thru .238 | 200.133.175.239 |
| 1111 | 200.133.175.240 | Reserved |
None
|
CIDR -- Classless InterDomain Routing
CIDR -- Classless
InterDomain Routing. CIDR was invented several
years ago to keep the internet from running out of IP addresses. The
"classful" system of allocating IP addresses can be very
wasteful; anyone who could reasonably show a need for more that 254
host addresses was given a Class B address block of 65533 host
addresses. Even more wasteful were companies and organizations that
were allocated Class A address blocks, which contain over 16 Million
host addresses! Only a tiny percentage of the allocated Class A and
Class B address space has ever been actually assigned to a host
computer on the Internet.
People realized that addresses could be conserved if the class
system was eliminated. By accurately allocating only the amount of
address space that was actually needed, the address space crisis
could be avoided for many years. This was first proposed in 1992 as a
scheme called Supernetting. Under supernetting, the classful
subnet masks are extended so that a network address and subnet mask
could, for example, specify multiple Class C subnets with one
address. For example, If I needed about 1000 addresses, I could
supernet 4 Class C networks together:
192.60.128.0 (11000000.00111100.10000000.00000000) Class C subnet address 192.60.129.0 (11000000.00111100.10000001.00000000) Class C subnet address 192.60.130.0 (11000000.00111100.10000010.00000000) Class C subnet address 192.60.131.0 (11000000.00111100.10000011.00000000) Class C subnet address -------------------------------------------------------- 192.60.128.0 (11000000.00111100.10000000.00000000) Supernetted Subnet address 255.255.252.0 (11111111.11111111.11111100.00000000) Subnet Mask 192.60.131.255 (11000000.00111100.10000011.11111111) Broadcast address
In this example, the subnet 192.60.128.0 includes all the addresses
from 192.60.128.0 to 192.60.131.255. As you can see in the binary
representation of the subnet mask, the Network portion of the address
is 22 bits long, and the host portion is 10 bits long.
Under CIDR, the subnet mask notation is reduced to a simplified
shorthand. Instead of spelling out the bits of the subnet mask, it is
simply listed as the number of 1s bits that start the mask. In the
above example, instead of writing the address and subnet mask as 192.60.128.0, Subnet Mask 255.255.252.0 the network address would be written simply as: 192.60.128.0/22 which indicates starting address of the network, and number of 1s
bits (22) in the network portion of the address. If you look at the
subnet mask in binary (11111111.11111111.11111100.00000000),
you can easily see how this notation works.
The use of a CIDR notated address is the same as for a Classful
address. Classful addresses can easily be written in CIDR notation
(Class A = /8, Class B = /16, and Class C = /24)
It is currently almost impossible for an individual or company to
be allocated their own IP address blocks. You will simply be told to
get them from your ISP. The reason for this is the ever-growing size
of the internet routing table. Just 10 years ago, there were less
than 5000 network routes in the entire Internet. Today, there are
over 100,000. Using CIDR, the biggest ISPs are allocated large chunks
of address space (usually with a subnet mask of /19 or even smaller);
the ISP's customers (often other, smaller ISPs) are then allocated
networks from the big ISP's pool. That way, all the big ISP's
customers (and their customers, and so on) are accessible via 1
network route on the Internet.
Your IP Address Information
Thanks for Reading
