The Future of IPv4

As mentioned earlier, allocation of blocks of IP addresses is the responsibility of the Internet Assigned Numbers Authority. IANA long ago delegated the job of allocating network prefixes to individual sites; they limited themselves to handing out /8 blocks (class A blocks) to the five regional registries, which are

• ARIN – North America

• RIPE – Europe, the Middle East and parts of Asia

• APNIC – East Asia and the Pacific

• AfriNIC – most of Africa

• LACNIC – Central and South America

In September 2015, ARIN ran out of its pool of IPv4 addresses. Most of ARIN’s customers are ISPs, which can now obtain new IPv4 addresses only by buying unused address blocks from other organizations.

A few months after the IANA pool ran out, Microsoft purchased 666,624 IP addresses (2604 Class-C blocks) in a Nortel bankruptcy auction for $7.5 million. By a year later, IP-address prices appeared to have retreated only slightly. It is possible that the market for IPv4 address blocks will continue to develop; alternatively, this turn of events may accelerate implementation of IPv6, which has 128-bit addresses.

An IPv4 address price in the range of $10 is unlikely to have much impact in residential Internet access, where annual connection fees are often $600. Large organizations use NAT (7.7 Network Address Translation) extensively, leading to the need for only a small number of globally visible addresses. The IPv4 address shortage does not even seem to have affected wireless networking. It does, however, lead to inefficient routing tables, as a site that once had a single /20 address block – and thus a single backbone forwarding-table entry – might now be spread over more than a hundred /27 blocks and concomitant forwarding entries.

DNS

IP addresses are hard to remember (nearly impossible in IPv6). The domain name system, or DNS , comes to the rescue by creating a way to convert hierarchical text names to IP addresses. Thus, for example, one can type www.luc.edu instead of 147.126.1.230. Virtually all Internet software uses the same basic library calls to convert DNS names to actual addresses.

One thing DNS makes possible is changing a website’s IP address while leaving the name alone. This allows moving a site to a new provider, for example, without requiring users to learn anything new. It is also possible to have several different DNS names resolve to the same IP address, and – through some modest trickery – have the http (web) server at that IP address handle the different DNS names as completely different websites.

DNS is hierarchical and distributed. In looking up cs.luc.edu four different DNS servers may be queried: for the so-called “DNS root zone”, for edu, for luc.edu and for cs.luc.edu. Searching a hierarchy can be cumbersome, so DNS search results are normally cached locally. If a name is not found in the cache, the lookup may take a couple seconds. The DNS hierarchy need have nothing to do with the IP-address hierarchy.