CIDR vs VLSM: When to Use Which

CIDR (Classless Inter-Domain Routing) and VLSM (Variable Length Subnet Masking) are two sides of the same coin.

CIDR — summarise routes

CIDR lets you combine several networks into one route. Four contiguous /24s become a single /22.

VLSM — right-size each subnet

VLSM lets each subnet be exactly as big as it needs to be: a 60-host LAN gets a /26, while a 2-host WAN link gets a /30 (or /31).

Design with our VLSM Calculator and summarise with the Supernet tool.