CIDR provides numerous advantages over the “classful” addressing scheme, whether or not subnetting is used:

• Efficient Address Space Allocation:

  i. Instead of allocating addresses in fixed-size blocks of low granularity, under CIDR addresses are allocated in sizes of any binary multiple.

  ii. So, a company that needs 5,000 addresses can be assigned a block of 8,190 instead of 65,534. Or, to think of it another way, the equivalent of a single Class B network can be shared amongst 8 companies that each need 8,190 or fewer IP addresses.

• Elimination of Class Imbalances:

  i. There are no more class A, B and C networks, so there is no problem with some portions of the address space being widely used while others are neglected.

• Efficient Routing Entries:

  i. CIDR's multiple-level hierarchical structure allows a small number of routing entries to represent a large number of networks.

  ii. Network descriptions can be “aggregated” and represented by a single entry.

  iii. Since CIDR is hierarchical, the detail of lower-level, smaller networks can be hidden from routers that move traffic between large groups of networks.

• No Separate Subnetting Method:

  i. CIDR implements the concepts of subnetting within the internet itself.

  ii. An organization can use the same method used on the Internet to subdivide its internal network into subnets of arbitrary complexity without needing a separate subnetting mechanism.