VLSM - Variable Length Subnet Mask

VLSM 
Variable length subnet mask is a technique that allows a network administrator to divide an IP address space into subnets of different sizes.


Subnetting
Allows you to create multiple logical networks that exist within a single class network.


Reasons why we subnet

• It helps the preservation of address space in order not to waste address
• It used for security
• It helps to control network traffic due to collision of packets transmitted by other nodes on the same segment

Legend

Δ	= Bit value
Sm	= Subnet Mask
UIP	= Usable IP
NA	= Notable Address

   
       32
       - n   

where n = bits

VLSM Table