| The adoption of a new addressing
scheme such as IPv6 requires time to design and implement. The
growth of the internet required interim solutions in order to
survive the demand for growth; this mandates
the implementation of new IP addressing strategies. This section
summarizes these strategies, their relative merits, and the issues
surrounding address assignment on the Internet.
Addressing strategies are of direct
and fundamental relevance to routing architecture. One of the basic
functions of routing architecture and routers is to accommodate
addresses for all the traffic that they direct. With the explosive
growth of the Internet, the sheer number of addresses and the
evolution of new addressing strategies have presented new challenges
for routing architecture. Throughout this chapter, we will note
particular routing rules and issues as they pertain to IP
addressing.
Since the 1980s, several solutions
have been developed to slow the depletion of IP addresses and to
reduce the number of Internet route table entries by enabling more
hierarchical layers in an IP address. The solutions discussed in
this chapter are as follows:
--- RFC
950 (1985); 1812 (1995). Developed to add another level of
hierarchy to an IP address. This additional level allows for
extending the number of network addresses derived from a single IP
address. (Discussed in Introduction to Cisco Router
Configuration, ISBN: 1-57870-076-0, by Cisco Press.)
Variable-Length Subnet Masks ---
RFC
1009 (1987). Developed to allow the network designer to utilize
multiple address schemes within a given class of address. This
strategy can be used only when it is supported by the routing
protocol, such as OSPF and EIGRP.
Address Allocation for Private
Internets --- RFC 1918
(1996). Developed for organizations that do not need much access to
the Internet. The only reason to have a NIC-assigned IP address is
to interconnect to the Internet. Any and all companies can use the
privately assigned IP addresses within the organization, rather than
using a NIC-assigned IP address unnecessarily.
Network Address Translation
--- RFC
1631 (1994). Developed for those companies that use private
addressing or use non-NIC-assigned IP addresses. This strategy
enables an organization to access the Internet with a NIC- assigned
address without having to reassign the private or
"illegal" addresses that are already in place.
Classless Inter-Domain Routing (CIDR)
--- RFCs
1518 and 1519 (1993). This is another method used for and developed
for ISPs. This strategy suggests that the remaining IP addresses be
allocated to ISPs in contiguous blocks, with geography being a
consideration.
These solutions will be discussed
later in the chapter.
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