Variable-Length Subnet Masking (VLSM) is a subnetting technique that allows network administrators to allocate IP addresses more efficiently by using different subnet masks for different network segments.
This enables the creation of subnets of varying sizes based on the specific needs and number of hosts in each subnet, reducing the waste of IP addresses and better utilizing the available IP space. VLSM is particularly useful in scenarios where different subnets require a different number of IP addresses, as it allows for a more precise allocation of IP addresses without wasting resources. This technique requires more advanced planning, design, and administration than the traditional Fixed Length Subnet Masking (FLSM) approach, but it provides greater flexibility and efficiency in IP address allocation.
VLSM is supported by various routing protocols such as OSPF, EIGRP, BGP, RIPv2, and IS-IS.