|One Byte at a Time: Internet Addressing
by Peter H. Salus
The source of all knowledge where the Internet is concerned is the set of Requests for Comments (RFCs). Because there are now well over 2,700 RFCs, however, only a few people track history, evolution, and outright paradigm shift.
Each node on the Internet-router or end system (often called "host" or "server") has a unique identifier attached to it; this identifier is its address . Any packet sent between nodes must use the destination address to tell the intervening routers where it should go.
In RFC 1 (April 1969), Steve Crocker laid out a scheme that allotted five bits to address space: enough for 32 addresses. By September 1969, when Interface Message Processor (IMP) No. 1 was installed in Kleinrock's lab at UCLA, this number had grown to six bits (63 addresses). By 1972, it had become apparent that this number would be insufficient, and the address space was enlarged to eight bits (255 addresses). In fact, the Advanced Research Projects Agency Network (ARPANET) hit only 63 hosts in January 1976. This number was, however, already a lot in terms of the HOSTS.TXT tables that were distributed to every site. By August 1983, there were 213 hosts, and the eight-bit address barrier was being pushed.
Cerf's original version of TCP (RFC 675; December 1974) and Postel's of IP (RFC 760; January 1980) increased this "address space" to 32 bits, but the structure of the ARPANET was "flat," that is, the hierarchical distributed name-to-address database we are familiar with only came about with Mills' conceptualization of the Domain Name System (DNS) (RFC 799; September 1981), and its implementation by Paul Mockapetris (RFCs 882 and 883; November 1983).
In August 1990 during the Vancouver Internet Engineering Task Force (IETF) meeting, Frank Solensky, Phill Gross, and Sue Hares projected that the current rate of assignment would exhaust the Class B space by March 1994.
Even with this palliative, it was predicted in 1994 that, using the current allocation statistics, the Internet will exhaust the IPv4 address space between 2005 and 2011. With five more years of experience, which has also brought greater uncertainty as to gross numbers, we can push these dates out a bit, but exhaustion will come eventually.
Another factor that has slowed down the address depletion rate is the use of Network Address Translation (NAT). NAT devices allows an organization to have one external ("public") address and many private (net 10 is often used) addresses internally. Since the internal addresses are not "seen" from the outside, they do not need to be globally unique. This approach has downsides (some protocols weren't designed with NATs in mind), but from the address depletion point of view, it is a win. RFC 1597 describes "Address Allocation for Private Internets."
If you are interested in current Internet addressing, an excellent book is available: TCP/IP Addressing , by Buck Graham, AP Professional, 1997. Graham does an excellent job on addressing, routing, and the various bizarreness involved in optimal routing, efficient use of address space, and making network management less onerous. This book is, however, not intended to be for elementary instruction; Graham primarily speaks to the professional market.
IPng aka IPv6
Unfortunately, as Bradner and Mankin stated in their recommendation: "Some people pointed out that this type of projection makes an assumption of no paradigm shifts in IP usage. If someone were to develop a new 'killer application,' (for example, cable-TV set top boxes), the resultant rise in the demand for IP addresses could make this an over-estimate of the time available."
IPv6 provides for 128-bit addressing. This number is gigantic: larger than the estimated total number of molecules in the universe.
There has been much discussion about various kinds of transition mechanisms, and some of these may be less painful (more automated) than we might at first think. Remember, this pain is not because of the innate difficulty, but veering a ship that carries fewer than 250 passengers is far easier than veering a ship that carries 60 million. Some members of the community think that the pain may not justify the gain. The author is not one of them. It has been nearly 20 years since TCP/IP was made official, yet there are still UUCP networks.
In the author's opinion, IPv6 will be here in a few years, if not sooner.