HP-UX LAN Administrator's Guide (July 2003)

DRAFT COPY Network Addressing
CIDR - Classless Inter-Domain Routing
Chapter 6 137
CIDR - Classless Inter-Domain Routing
As the Internet has evolved and grown in recent years, it has become clear that it is facing
several serious problems. These include:
• Exhaustion of the Class B network address space. One fundamental cause of the problem
is the lack of a network class of a size that is appropriate for a mid-sized organization.
Class-C, with a maximum of 254 host addresses, is too small, while Class-B, which allows
up to 65534 addresses, is too large to be densely populated. The result is inefficient
utilization of Class-B network numbers.
• Routing Information overload. The size and rate of growth of the routing tables in
Internet routers is beyond the ability of current software (and people) to effectively
manage.
Classless Inter-Domain Routing (CIDR) attempts to deal with these problems by defining a
mechanism to slow the growth of routing tables and reduce the need to allocate new IP
network numbers.