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... Internet is currently faced with two major operational problems
(amoung others). The first is the eventual exhaustion of the IPv4
address space and the second is the ability to route packets between
the large number of individual networks ...
... networks that make up the Internet.
The first problem is simply one of supply. There are only 2^32 IPv4
addresses available. The lifetime of that space is proportional to
the efficiency of its allocation and utilization. The second problem
...
... LAN technologies, it became
obvious that this assumption was wrong and the separation of the
address space into three classes (Class A for a few huge networks ...
... network number (Class A, B, or C) into pieces, allowing a
higher utilization of address space, and thus promoting conservation
of the IPv4 address space. Because of the built-in notion of
...
... higher utilization of address space, and thus promoting conservation
of the IPv4 address space. Because of the built-in notion of
classful addresses, subnetting automatically induced a reduction in
...
... of the IPv4 address space. Because of the built-in notion of
classful addresses, subnetting automatically induced a reduction in
the routing requirements ...
...
Since 1993, the concept of classless (the "C" in CIDR) addresses have
been introduced to the Internet community. Addresses ...
... addresses have
been introduced to the Internet community. Addresses are
increasingly thought of as bitwise contiguous blocks of the entire
address space ...
... Addresses are
increasingly thought of as bitwise contiguous blocks of the entire
address space, rather than a class A,B,C network. For example, the
...
... class A,B,C network. For example, the
address block formerly known as a Class A network, would be referred
...
... prefix, meaning the first 8 bits of the
address define the network portion of the address. Sometimes the /8
...
... address define the network portion of the address. Sometimes the /8
will be expressed as a mask of 255.0.0.0 (in the same way a 16 bit
...
...
This scheme allows "supernetting" of addresses together into blocks
which can be advertised as a single routing entry. The practical
...
... routing entry. The practical
purpose of this effort is to allow service providers and address
registries to delegate realistic address spaces ...
... address
registries to delegate realistic address spaces to organizations and
be unfettered by the traditional network classes ...
... subnet mask written
in dotted decimal notation). The concept of "supernetting" allows
the remaining Internet address space to be allocated in smaller
blocks, thus allowing more networks and better efficiency. For a
...
... CIDR blocks are allocated in a way which promotes hierarchical
routing. A provider is typically given a large block of addresses to
redistribute to their customers. For example, if the provider ...
...
The good news is that CIDR is working. Address blocks are being
allocated and assigned in a hierarchical manner, and the CIDR'ization
...
... allocated and assigned in a hierarchical manner, and the CIDR'ization
of large portions of the address space which were assigned according
to the guidelines of RFC 1466(-> 2050) resulted in a significant drop of
...
... networks being connected.
(Registries are still allocating a few addresses not within CIDR
blocks, so a small third source does exist.) With increasing
...
... provider and retains the use of their CIDR block
addresses, holes appear in the blocks and specific routes are added
to the routing structure to accommodate these cases. Thus over time,
...
... routing structure to accommodate these cases. Thus over time,
CIDR will improve address utilization efficiency yet not help the
routing requirements ...
...
The IANA has historically managed the assignment of addresses to
Internet sites. During the earliest days of the IANA ...
... Internet sites. During the earliest days of the IANA, given a vast
address space, the requirements for assignments of network address
space ...
... address space, the requirements for assignments of network address
space were much less stringent than those required today.
Organizations were essentially assigned networks based on their
...
...
The upper half of the Class A address space (64.0.0.0 - 126.0.0.0)
(127.0.0.0 has traditionally been used by the Unix operating system
...
... unavailable) has been reserved
by the IANA for growth within the IPv4 address space. Of the lower
half of the address space, 22 were assigned pre-1982, 6 were assigned
...
... IANA for growth within the IPv4 address space. Of the lower
half of the address space, 22 were assigned pre-1982, 6 were assigned
between 1982 and 1987, 26 were assigned between 1988 and 1992, and 2
were assigned between 1993 and 1995. In May of 1995 four Class ...
... IANA. All
remaining Class A addresses have also been reserved for growth within
the IPv4 address space. The Class ...
... Class A addresses have also been reserved for growth within
the IPv4 address space. The Class A address space is 50% of the total
...
... outlined in RFC 1466(-> 2050). 61.65% of the Class B address space is
currently allocated. The class B address space ...
... address space is
currently allocated. The class B address space is 25% of the total
IPv4 address space.
...
... 1466(-> 2050) the allocation of Class C
address space has skyrocketed since 1993. 27.82% of the Class C
address space ...
... address space has skyrocketed since 1993. 27.82% of the Class C
address space is currently allocated. The class C address space is
...
... address space is currently allocated. The class C address space is
12.5% of the total IPv4 address space.
...
...
Of the remaing 12.5% of the address space, the lower 6.25% is
allocated for multicast applications (mbone, OSPF ...
...
The weighted total shows that 40.99% of the total IPv4 address space
is allocated and the remainder is reserved for future growth. It
should be noted that careful extrapolations of the current trends
...
... is allocated and the remainder is reserved for future growth. It
should be noted that careful extrapolations of the current trends
suggest that the address space will be exhausted early in the next
century.
...
...
Current Internet sites have received their address assignments in
various ways and steps. Some sites, through a little (or in some
cases no) work, could donate unused IP ...
... Internet service providers were given blocks of the Class B
address space to distribute to customers. This space was often
provided to clients ...
... Many organizations have either merged or are associated with parent
organizations which produce situations with large inefficiencies in
address assignment.
...
...
Many organizations have requested addresses based on their need to
run TCP/IP on internal machines which have no interest in connecting
...
... Internet. Most vendors manuals have instructed (and
provided copies of the application forms), sites to request IP
address assignments.
...
... application layer gateways or
network address translators, and will never announce their internal
networks.
...
... assignments which may be currently unused, the Internet community
would like to encourage you to return those addresses to the IANA or
your provider ...
... Specifically those sites who have networks which are unused are
encouraged to return those addresses. Similarly to those sites who
are using a small percentage of their address space and who could
...
... encouraged to return those addresses. Similarly to those sites who
are using a small percentage of their address space and who could
relatively easily remove network ...
... Internet, or for security reasons will always be isolated,
consider returning the address assignments to the IANA or your
provider ...
... Many providers are currently advertising non-CIDR routes which
encompass a large block of addresses, ie any Class A (0/1) or Class B
...
... (128/2) space. Some customers who are only using a percentage of
their address space (assuming they are subnetting using contiguous
bits) may be willing to allow usage of the upper portion of their
...
... bits) may be willing to allow usage of the upper portion of their
assigned address space by their providers other customers.
...
... For example, large organization S has been assigned the class A block
of addresses 10.0.0.0. and is currently using provider P for their
connection ...
... allow P to attach a huge number of small customers without the need
to advertise more routes or request additional address blocks from
the IANA or their upstream ...
... Additionally, providers are encouraged to release all unused networks
which fall outside of their normal address blocks back to the IANA or
the appropriate registry ...
... CIDR'ized blocks, should be encouraged to renumber and release their
previous addresses back to the provider or the IANA.
...
... addresses are returned to the IANA, or any other
address registry, which fits into another registry or providers
...
... registry, which fits into another registry or providers
block, the addresses should be turned over to the appropriate
authority. This will help maximize the availability of addresses ...
... addresses should be turned over to the appropriate
authority. This will help maximize the availability of addresses and
minimize routing table loads.
...
... How to Return a Block of Address Space to the IANA ...
...
Each registry will have its own forms and addresses. Please contact
the appropriate registry directly.
...
... IANA. This may not seem significant but those 4
networks represent over 1.5% of the total IPv4 address capacity.
...
... Gerich, E., "Guidelines for Management of the IP Address Space", RFC 1466(-> 2050), May 1993. ...
... Rekhter, Y., and T. Li, "An Architecture for IP Address Allocation with CIDR", RFC 1518hist, September 1993. ...
... Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC 1519(-> 4632), September 1993. ...
... Rekhter, Y., Moskowitz, R., Karrenberg, D., and de Groot, G., "Address Allocation for Private Internets", RFC 1597(-> 1918), March 1994. ...
... Huitema, C., "The H Ratio for Address Assignment Efficiency", RFC 1715, November 1994. ...
... Author's Address ...