Why a New IP?

The IP addressing system described in Hour 4, “The Internet Layer,” has served the Internet community for nearly a generation, and those who developed it are justifiably proud of how far TCP/IP has come. But the Internet community has one big problem: The world might run out of addresses. This looming address crisis might seem surprising, because the 32-bit address field of the current IP format can provide over three billion possible host IDs. But it is important to remember how many of these three billion addresses are actually unusable.

A network ID is typically assigned to an organization, and that organization controls the host IDs associated with its own network. Recall from Hour 4 that IP addresses were originally intended to fall within address classes determined by the value of the first octet in the address field. The address classes and their associated address ranges are shown in Table 13.1, which also shows the number of possible networks within an address class and the number of possible hosts on each network. A Class B address can support 65,534 hosts. Many Class B organizations, however, do not have 65,534 nodes and, therefore, assign only a fraction of the available addresses. The 127 Class A networks can support 16,777,214 addresses, many of which also go unused. It is worth noting as well that the 16,510 Class A and B networks are reportedly all taken. The Class C networks that remain face a limitation of only 254 possible addresses. (Refer to Hour 4 and Hour 5, “Subnetting and CIDR,” for more on the anatomy of IP addresses.)

Fortunately, the use of Network Address Translation (NAT) has reduced the need for Internet-ready addresses, and the CIDR classless address system described in Hour 5 has found homes for many of the lost addresses. At the same time, however, other recent developments, such as the rise of mobile networking, have placed renewed pressure on the address space.

Internet philosophers have discussed a transition to a new addressing system for some time. And, because the system was due for an overhaul anyway, they also proposed additional enhancements to IP to add new features and integrate new technologies. This new system eventually crystallized into IP version 6 (IPv6), which is sometimes called IPng for IP next generation. The current IPv6 specification is RFC 2460, which appeared in December 1998. (Several other preliminary RFCs set the stage for RFC 2460, and newer RFCs continue to discuss issues relating to IPv6.)

The IP address format in IPv6 calls for 128-bit addresses. Part of the reason for this larger address space is supposedly to support one billion networks. As you learn later in this hour, this large address size is also spacious enough to accommodate some compatibility between IPv4 addresses and IPv6 addresses.

Some of the goals for IPv6 are as follows:

• Expanded addressing capabilities— Not only does IPv6 provide more addresses, it also provides other improvements to IP addressing. For instance, IPv6 supports more hierarchical addressing levels. IPv6 also improves address auto-configuration capabilities and provides better support for anycast addressing, which enables an incoming datagram to arrive at the “nearest” or “best” destination given a group of possible targets.

• Simpler header format— Some of the IPv4 header fields have been eliminated. Other fields have become optional.

• Improved support for extensions and options— IPv6 includes some header information in optional extension headers. This approach increases the range of possible information fields without wasting space in the main header. In most cases, these extension headers are not processed by routers; this further streamlines the transmission process.

• Flow labeling— IPv6 datagrams can be marked for a specific flow level. A flow level is a class of datagrams that requires specialized handling methods. For instance, the flow level for a real-time service might be different from the flow level of an email message. The flow level setting can be useful for ensuring a minimum quality of service for the transmission.

• Improved authentication and privacy— IPv6 extensions support authentication, confidentiality, and data integrity techniques.

As of this writing, IPv6 has been ready for nearly 10 years, yet very few networks have actually implemented it as a complete system. Part of the problem is that this change to the next generation requires a transition in which both IPv4 and IPv6 are simultaneously supported, and as long as IPv4 is working, admins have no compelling reason to stop using it. As of now, all major operating systems and most routers offer IPv6 support. Most organizations, however, do not expend the overhead to actively maintain both systems (although an IPv6 stack might be running by default).

Even if an organization wants to implement a native IPv6 network at the local level, they might run into problems finding an Internet service provider that offers native IPv6 support. Internet IPv6 service is often available through IPv6 tunnel brokers. A tunnel broker encapsulates IPv6 packets within an IPv4 tunnel. This approach does indeed provide IPv6 connectivity at the end points, but supporting IPv6 through an IPv4 tunnel reduces the effect of the advanced routing and quality of service features built into IPv6.

An Internet draft currently available through the IETF outlines a path to full IPv6 implementation by January 2012. According to the plan, at the end of this transition, Internet providers must offer IPv6 services (and should provide native IPv6 services), organizations must provide IPv6 connectivity for Internet-facing servers, and organizations should support internal IPv6 connectivity. The draft is set to expire on August 2008; presumably an updated version will be available by the time this book reaches print.

IPv6 networking is already starting to appear more frequently in OS documentation and training curricula. If the transition outlined in the current Internet draft is successful, the next edition of this book will probably be the IPv6 edition, and the topic of IPv6 will inhabit Hour 4 instead of Hour 13. In the meantime, this hour outlines some important IPv6 concepts.