CIDR

• Eg: allocate class Cs from 194.0.0.0 thru 195.255.255.255 for hosts in Europe (higher order 7 bits the same).

  • Allows one routing entry for Europe

• Allow other routing entries too. Eg: 194.0.160 + mask of 255.255.240.0

  • When an address matches multiple entries (eg 194.0.22.1), choose the one which had the longest mask (“longest-prefix match”)

• Routing decisions independent of class

• Slows down router table growth.

  • If hosts renumbered, router sizes would drastically reduce.

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