Saturday, January 29, 2011

Subnetting

Subnetting
Simple Steps to perform Subnetting:

You have a class C  address of 192.168.100.0/24. You need 9 Subnets
-What is the IP plan of network numbers;
-broadcast numbers
-valid host numbers
-Subnet mask needed for this plan


Step1:
Determine how many H bits you need to borrow to create 9 valid subnets
2N-2 >= 9
 N=4, so you need to borrow 4 H bits and turn them into N bits

Start with 8bits                       HHHH HHHH
Borrow 4 bits                          NNNN HHHH
Step2: Determine the first valid subnet in binary
0001 HHHH               Cannot use subnet 0000 because it is invalid
0001 0000                   Subnet Number
0001 0001                   First Valid Host Number
.
.
.
.
.
0001 1110                   Last Valid Host number
0001 1111                   Broadcast address

Step 3: Convert Binary into Decimal

0001 0000=16
0001 0001=17
.
.
.
.
0001 1110=30
0001 1111=31

Step 4: Determine the second Valid subnet in binary

0010 HHHH               0010=2 in binary=second valid subnet
0010 0000                   Subnet work number
0010 0001                   First valid host number
.
.
.
.
.
0010 1110                   Last valid host number
0010 1111                   Broadcast number

Step 5 Convert binary into decimal

0010 0000=32             Subnetwork
0010 0001=33             First Valid host number
.
.
.
.
0010 1110=46             Last Valid Host number
0010 1111=47             Broadcast number

Step 6: Create an IP plan table

Valid subnet   Network Number   Range of Valid Hosts    Broadcast number
1                                  16                    17-30                           31
2                                  32                    33-46                           47
3                                  48                    49-62                           63



Step 7 Finish the IP plan table

Subnet 0                     192.168.100.0
                                    192.168.100.15

Subnet 1                     192.168.100.16
                                    192.168.100.31

Subnet 2                     192.168.100.32
                                    192.168.100.47

Subnet 3                     192.168.100.48
                                    192.168.100.63

Subnet 4                     192.168.100.64
                                    192.168.100.79

And the list goes on……


Step 8 Calculate the subnet mask

Default Subnet mask for Class C is 255.255.255.0

i.e 1111 1111.1111 1111.1111 1111.0000 0000
We have borrowed 4 bits. Therefore
1111 1111.1111 1111.1111 1111.1111 0000
i.e 255.255.255.240



Subnetting Class B is also very much similar to this, but we have to start with 16 Host bits
Eg

If N=4

Start with 16 H bits  HHHH HHHH.HHHH HHHH
Borrow 4 bits            NNNN HHHH.HHHH HHHH



No comments:

Post a Comment