| A relatively recent addition to the IP
address architecture is CIDR (pronounced "Cider").
CIDR was born of the crisis that accompanied the Internet's
explosive growth during the early 1990s.
As early as 1992, the IETF became
concerned with the Internet's capability to continue to scale upward
in response to demand for Internet use. Their specific concerns were
as follows:
- Exhaustion of the remaining,
unassigned IPv4 network addresses. The Class B space was in
particular danger of depletion.
- The rapid, and substantial,
increase in the size of the Internet's routing tables as a
result of its growth.
All the indications were that the
Internet's rapid growth would continue, as more commercial
organizations came online. In fact, some members of the IETF even
predicted a "Date of Doom". This date, March 1994, was the
projected date of the depletion of the Class B address space. Absent
any other mechanism for addressing, the Internet's scalability would
be seriously compromised. More ominously, the Internet's routing
mechanisms might collapse under the weight of their ever-growing
routing tables before the "Date of Doom".
The Internet was becoming a victim of
its own success. The IETF decided that, to avoid the collapse of the
Internet, both short- and long-term solutions would be needed. In
the long term, the only viable solution was a completely new IP,
with greatly expanded address space and address architectures.
Ultimately, this solution became known as IPng (Internet Protocol:
The Next Generation) or, more formally, as IP Version 6 (IPv6).
The more pressing, short-term needs
were to slow down the rate of depletion of the remaining unassigned
addresses. The answer was to eliminate the inefficient classes of
addresses in favor of a more flexible addressing architecture. The
result was CIDR.
In September 1993, the plans for CIDR
were released in RFCs 1517, 1518, 1519, and 1520. CIDR had three key
features that were invaluable in staving off depletion of the IPv4
address space. These features are the following:
- The replacement of classful
addressing by classless
- Enhanced route aggregation
- Supernetting
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