2.3 IP Address Issues and Solutions
2.3.3 Slowing IP address depletion
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:

  • Subnet Masking --- 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.