Question : subnetting

what is subnetting?how is it done?suppose 198.53.202.0 is a network address and we want 4 subnets.find the following

1)number of bits required for subnetting
2)standard sunbnet mask
3)custom subnet mask
4)starting host id
5)last host id for each subnet.

i have my network exam coming up so please explain me the solutions i m currently refering furozan and tannenbaum

Answer : subnetting

All classes of IP networks can be divided into smaller networks called subnetworks or subnets. And the process is called subnetting.

Well before going to the answers, first you should know the IP Address Classes. There are 3 IP classes. Class A, Class B & Class C. These are also called commercial classes.

In Class A address, the first octet is the network portion, so the Class A address of 10.1.25.1, has a major network address of 10. Octets 2,3 & 4 or say next 24 bits are the hosts. Class A addresses can be used for more than 65536 hosts.

In Class B, the first two octet is network portion. Now, 172.16.122.204 is a Class B IP address where 172 & 16 are the major network address & octets 3 & 4 are hosts.
Range between 256 to 65536 hosts.

In Class C, the first 3 octets are network portion & the last one is hosts. So 193.18.9.40 here 193.18.9 is for network portion & 40 is host. In Class C there can hosts less than 254.

Now, to solve ur problem, the first duty is to classify in which class you IP is, from First Octet Rule, as follows...

ADDRESS CLASS          FIRST OCTET in DECIMAL             HIGH-ORDER BITS
--------------------         ------------------------------             ---------------------
Class A                       1-126                                           0
Class B                       128-191                                       10
Class C                       192-223                                       110

So, form the above chart we can say that the IP 198.53.202.0 is a Class C address, as we can see the first octet lies between 192-223.

So, in Class C address the last octet is for host. So 198.53.202.1, 198.53.202.2, 198.53.202.3, 198.53.202.4 can be said subnets of 198.53.202.0.

Here your answers...

1) 64
2) 255.255.255.0 [as this is the default subnet musk for Class C address] #
3) 255.255.255.192 *
4) Starting host ID is "0" followed by 64, 128 & 192 *
5) 192 *

*Explained:~ Using a subnet mask of 255.255.255.192, your 198.53.202.0 network then becomes the four networks 198.53.202.0, 198.53.202.64, 198.53.202.128 and 198.53.202.192. These four networks would have as valid host addresses, as required in your question.

# Standard Subnet Musks are as follows...

Class A - 255.0.0.0 [As last 3 octets are hosts]
Class B - 255.255.0.0 [As last 2 octets are hosts]
Class C - 255.255.255.0 [As last octet is for hosts]

So, as your address is a Class C address the standard subnet musk is 255.255.255.0

Hope now u can understand it well...
Milan