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Q & A IP & Network · September 11, 2026

What is the difference between /30 and /31?

/30 has 4 addresses (2 usable) — classic point-to-point link with 2 hosts, 1 network, 1 broadcast. /31 (RFC 3021, 2000) redefines the semantics: only 2 addresses, both are usable, no network / broadcast — a modern point-to-point link with zero waste. Most modern routers support /31 for backbone links to conserve address space.

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CIDR Subnet Math Explained: /24, /16, /8, and Everything Between
CIDR notation is how modern networks are described: an IP address plus a slash and a number counting the network-prefix bits. Everything left of the boundary is the network; everything right is the host. The math is simpler than the notation makes it look.
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How do I split a /24 into four subnets? How many hosts fit in a /16? Is /32 a valid subnet? What does /24 mean in an IP address? What is the difference between a public and private IP?