Full form: Fixed Length Subnet Masking
Also known as: Fixed Length Subnet Masking
Quick Definition
Using the same subnet mask length for all subnets in a network.
FLSM uses a single subnet mask size for all subnets derived from a major network. Every subnet has the same number of host addresses regardless of actual need. This is simpler to design but wasteful — a point-to-point WAN link gets the same large subnet as a building LAN. FLSM is typically only seen in networks using classful routing protocols such as RIPv1.
FLSM is associated with classful routing protocols (RIPv1) that do not carry subnet mask information. Modern networks use VLSM.
FLSM uses a single subnet mask size for all subnets derived from a major network. Every subnet has the same number of host addresses regardless of actual need. This is simpler to design but wasteful — a point-to-point WAN link gets the same large subnet as a building LAN. FLSM is typically only seen in networks using classful routing protocols such as RIPv1.
FLSM is associated with classful routing protocols (RIPv1) that do not carry subnet mask information. Modern networks use VLSM.
FLSM falls under the IP Addressing domain of the 200-301 exam. Understanding it in context with related terms like vlsm and cidr is essential for answering scenario-based questions correctly.