Variable Length Subnet Mask
Variable Length of Subnet Mask ( VLSM ) is a subnet mask with variable length. It was first documented in 1985 in RFC 950 and introduced in 1993 as Classless Inter-Domain Routing (CIDR) on the Internet ( RFC 1518 , RFC 1519 , replaced by RFC 4632 in 2006 ).
VLSM is an extended subnetting . This procedure allows a more efficient use of subnets with the background of "wasting" fewer resources. This is realized by assigning unique subnet masks to the previously established subnet ( subnet ).
Multiple, nested division of the address range creates a nested system of address blocks, each of which has a minimum size. This is sufficient in order to be able to supply the respective assigned subnets with a sufficient number of IP addresses .
The advantages are a more effective use of address ranges, the reduction in size of the routing tables by aggregating routes and an increased number of possible subnets.
A subnet 10.1.1.0/24 is reserved from the address block 10.1.0.0/16 for addressing point-to-point networks. The subnet 10.1.1.0/30, the second 10.1.1.4/30 etc. are then taken from this for the first point-to-point network.
- VLSM (CIDR) Subnet Calculator (Engl.)
- VLSM, exercise generator
- CIDR calculator, German, calculates all subnets
- RFC 950 : Internet Standard Subnetting Procedure (1985)
- RFC 1518 : An Architecture for IP Address Allocation with CIDR (1993)
- RFC 1519 : Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy (1993; status: historical)
- RFC 4632 : Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan