CIDR fixes IPv4 waste from old Class B blocks

Fri, 01 May 2026 12:56:18 +0000

Geoff Huston's CIDR Report has named and shamed inefficient networks for over two decades to curb routing bloat.

Classless Inter-Domain Routing (CIDR) remains the single most critical mechanism for preventing IPv4 exhaustion, a reality reinforced by rising address demand in 2026. By replacing the rigid Class A, B, and C structures of RFC 791 with flexible prefix lengths defined in RFC 1519, CIDR solved the twin crises of address scarcity and router table scalability. Readers will examine the historical transition from fixed-size blocks to the variable-length architecture that powers modern connectivity. We analyze how BGP4 mechanics use route aggregation to minimize the processing load on shared infrastructure, contrasting this with the inefficiencies of legacy models. Finally, we explore the operational influence of APNIC's reporting tools in driving behavioral changes among network operators who might otherwise ignore the collective cost of their routing announcements. (APNIC's the why and what of the cidr report))

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CIDR fixes IPv4 waste from old Class B blocks