Variable Length Subnet Mask (VLSM)
Basic subneting: refers to a fixed mask in addition to natural mask (i.e. class A, B etc).
- I.e. only a single mask (eg:: 255.255.255.0) can be used for all networks covered by the natural mask.
VLSM: Multiple different masks possible in a single class address space.
- Eg: 255.255.255.0 and 255.255.254.0 could be used to subnet a single class B address space.
- Allows more efficient use of address space.