UNDERSTANDING SUBNETTING

Understanding Subnetting

1.     A few more steps accomplish outside connection, including configuring a router, obtaining an ip address and actually making the connecting.

2.     IP numbers are not assigned to hosts, they are assigned to network interfaces on hosts.

3.     Subnetting is process of dividing single network address into multiple networks.

4.     Even though many computers on an IP network have a single network interface and a single IP number, a single computer can have more than one network interface.

5.     In the current (IPv4) implementation, IP numbers consist of 4 (8-bit) bytes for a total of 32 bits of available information.

6.     This system results in large numbers, even when they are represented in decimal notation. To make them easier to read and organize, they are written in what is called dotted quad format.

7.     Example the internal network IP address 192.168.1.1.  Each of the four groups of numbers can range from 0 to 255.

8.     Binary notation: If the bit is set to 1 it is counted, and if set to zero it is not counted.
The binary notation for 192.168.1.1 is;
11000000.10101000.00000001.00000001

9.     The dotted quad notation from this binary is:
(128+64).(128+32+8).(1).(1) = 192.168.1.1

Interpreting IP numbers

1.     IP numbers can have three possible meanings.

a.     The first of these is an address of a network, which is the number representing all the devices that are physically connected to each other.

b.     The second is the broadcast address of the network, which is the address that enables all devices on the network to be contacted.

c.      The last meaning is an actual interface address.

2.     Look at the Class C network for an example.

a.     192.168.3.0 is a Class C network number.

b.     192.168.3.42 is a host address on this network

c.      192.168.3.255 is the network broadcast address.

Before you subnet your Network

1.     First you need to decide the number of hosts on each of your subnets so you can determine how many IP addresses you need.

2.     Every IP network has two addresses that cannot be used – the network IP number itself and the broadcast address. Whenever you subnetwork the IP network you are creating additional addresses that are unusable

3.     Every IP network has two addresses that cannot be used — the network IP number itself and the broadcast address.

4.     Every time you subnet you are creating these two unusable addresses, so the more subnets you have, the more IP addresses you lose.

5.     Hence the point is, don’t subnet your network more than necessary.

6.     If you wanted to divide your Class C network into two subnetworks, you would change the first host bit to one and you would get a net mask of
11111111.11111111.11111111.10000000 or 255.255.255.128

7.     This would give you 126 possible IP numbers for each of your subnets because that you lose two IP address for each subnet.

8.     If you want to have four subnetworks, you need to change the first two host bits to ones and this would give you a netmask of 255.255.255.192 . You would have 62 IP addresses available hosts for your Class C networks.

9.     Now all you need to do is assign the appropriate numbers for the network, the broadcast address, and the IP addresses for each of the interfaces and you’re nearly done.

To create subnets for Class A and B networks, you follow the same procedure as that shown for Class C networks.