IPv6 to the rescue – eh?

June 21, 2007

To me, IPv6 is one of the Internet’s real enigmas as the supposed replacement of the the Internet’s ubiquitous IPv4. We all know this has not happened.

The Internet Protocol (IPv4) is the principle protocol that lies behind the Internet and it originated before the Internet itself. In the late 1960s there was a need in a number of US universities to exchange data and an interest in developing the new network technologies, switching capabilities and protocols required to achieve this.

The result of this was the formation of the Advanced Research Project Agency a US government body who started developing a private network called ARPANET which metamorphosed into the Defense Advanced Research Projects Agency (DARPA). The initial contract to develop the network was won by Bolt, Beranek and Newman (BBN) which was eventually bought by Verizon and sold to two private equity companies in 2004 to be renamed BBN Technologies.

The early services required by the university consortium were file transfer, email and the ability to remotely log onto university computers. The first version of the protocol was called the Network Control Protocol (NCP) and saw the light of day in 1971.

In 1973, Vince Cerf, who worked on NCP (now Chief Internet Evangelist at Google), and Robert Kahn ( who previously worked on the Interface Message Processor [IMP]) kicked off a program to design a next generation networking protocol for the ARPANET. This activity resulted in the the standardisation through ARPANET Requests For Comments (RFCs) of TCP/IPv4 in 1981 (now IETF RFC 760).

IPv4 uses a 32-bit address structure which we see most commonly written in dot-decimal notation such as aaa.bbb.ccc.ddd representing a total of 4,294,967,296 unique addresses. Not all of these are available for public use as many addresses are reserved.

An excellent book that pragmatically and engagingly goes through the origins of the Internet in much detail is Where Wizards Stay Up Late – it’s well worth a read.

The perceived need for upgrading

The whole aim of the development of of IPv4 was to provide a schema to enable global computing by ensuring that computers could uniquely identify themselves through a common addressing scheme and are able to communicate in a standardised way.

No matter how you look at it, IPv4 must be one of the most successful standardisation efforts to have ever taken place if measured by its success and ubiquity today. Just how many servers, routers, switches, computers, phones, and fridges are there that contain an IPv4 protocol stack? I’m not too sure, but it’s certainly a big, big number!

In the early 1990s, as the Internet really started ‘taking off’ outside of university networks, it was generally thought that the IPv4 specification was beginning to run out of steam and would not be able to cope with the scale of the Internet as the visionaries foresaw. Although there were a number of deficiencies, the prime mover for a replacement to IPv4 came from the view that the address space of 32 bits was too restrictive and would completely run out within a few years. This was foreseen because it was envisioned, probably not wrongly, that nearly every future electronic device would need its own unique IP address and if this came to fruition the addressing space of IPv4 would be woefully inadequate.

Thus the IPv6 standardisation project was born. IPv6 packaged together a number of IPv4 enhancements that would enable the IP protocol to be serviceable for the 21st century.

Work was started 1992/3 and by 1996 a number of RFCs were released starting with RFC 2460. One of the most important RFCs to be released was RFC 1933 which specifically looked at the transition mechanisms of converting IPv4 networks to IPv6. This covered the ability of routers to run IPv4 and IPv6 stacks concurrently – “dual stack” – and the pragmatic ability to tunnel the IPv6 protocol over ‘legacy’ IPv4 based networks such as the Internet.

To quote RFC 1933:

This document specifies IPv4 compatibility mechanisms that can be implemented by IPv6 hosts and routers. These mechanisms include providing complete implementations of both versions of the Internet Protocol (IPv4 and IPv6), and tunnelling IPv6 packets over IPv4 routing infrastructures. They are designed to allow IPv6 nodes to maintain complete compatibility with IPv4, which should greatly simplify the deployment of IPv6 in the Internet, and facilitate the eventual transition of the entire Internet to IPv6.

The IPv6 specification contained a number of areas of enhancement:

Address space: Back in the early 1990s there was a great deal of concern about the lack of availability of public IP addresses. With the widespread uptake of IP rather than ATM as the basis of enterprise private networks as discussed in a previous post The demise of ATM, most enterprises had gone ahead and implemented their networks with any old IP address they cared to use. This didn’t matter at the time because those networks were not connected to the public Internet so it did’nt matter whether other computers or routers had selected the same addresses.

It first became a serious problem when two divisions of a company tried to interconnect within their private network and found that both divisions had selected the same default IP addresses and could not connect. This was further compounded when those companies wanted to connect to the Internet and found that their privately selected IP addresses could not be used in the public space as they had been allocated to other companies.

The answer to this problem was to increase the IP protocol addressing space to accommodate all the private networks coming onto the public network. Combined with the vision that every electronic device could contain an IP stack, IPv6 increased the address space to 128 bits rather than IPv4′s 32 bits.

Headers: Headers in IPv4 (headers precede data in the packet flow and contain routing and other information about the data) were already becoming unwieldy so the addition of extra data in the headers necessitated by IPv6 would not help things by increasing a minimum 20byte header to 80 bytes. IPv6 headers are simplified by enabling headers to be chained together and only used when needed. IPv4 has a total of 10 fields, while IPv6 has only 6 and no options.

Configuration: Managing an IP network is pretty much of a manual exercise with few tools to automate the activity beyond tools such as DCHP (the automatic allocation of IP addresses for computers). Network administrators seem to spend most of the day manually entering IP addresses into fields in network management interfaces which really does not make much use of their skills.

IPv6 has incorporated enhancements to enable a ‘fully automatic’ mode where the protocol can assign an address to itself without human intervention. The IPv6 protocol will send out a request to enquire whether any other device has the same address. If it receives a positive reply it will add a random offset and ask again until it receives no rely. IPv6 can also identify nearby routers and automatically identify if a local DHCP server ID available.

Quality of Service: IPv6 has embedded enhancements to enable the prioritisation of certain classes of traffic by assigning a value to a packet in the field labelled Drop Priority.

Security: IPv6 incorporates IP-Sec to provide authentication and encryption to improve the security of packet transmission and is handled by the Encapsulating Security Payload (ESP).

Multicast: Multicast addresses are group addresses so that packets can be sent to a group rather than an individual. IPv4 handles this very inefficiently while IPv6 has implemented the concept of a multicast address into its core.

So why aren’t we all using IPv6?

The short answer to this question is that IPv4 is a victim of its own success. The task of migrating the Internet to IPv6, even taking into to account the available migration options of dual stack hosting and tunnelling, is just too challenging.

As we all know, the Internet is made up of thousands of independently managed networks each looking to commercially thrive or often just to survive. There is no body overseeing how the Internet is run except for specific technical aspects such as Domain Name Server (DNS) management or the standards body, IETF. (Picture credit: The logo of Linux IPv6 Development Project)

No matter how much individual evangelists push for the upgrade, getting the world to do so is pretty much an impossible task unless everyone sees that there is a distinct commercial and technical benefit for them to do so.

This is the core issue and as the benefits of upgrading to IPv6 have been seriously eroded by the advent of other standards efforts that address each of the IPv6 enhancements on a stand-alone basis. The two principle are NAT and MPLS.

Network address translation (NAT): To overcome the limitation in the number of available public addresses, NAT was implemented. This means that many users / computers in a private network are able to access the public Internet using a single public IP address. Each user is assigned a transient dynamic session IP address when they access the Internet and the NAT software manages the translation between the the public IP address and the dynamic address used within the private network.

NAT effectively addressed the concern that the Internet may run out of address space. It could be argued that NAT is just a short term solution that came at a big cost to users. The principle downside is that external connections are unable to set up long term relationships with an individual user or computer that is behind a NAT wall as they have not been assigned their own unique IP address. Users of the internal dynamically assigned IP addresses can change at any time.

This particularly affects applications that contain addresses so that traffic can always be sent to a specific individual or computer – VoIP is probably the main victim.

It’s interesting to note that the capability to uniquely identify individual computers was the main principle behind the development of IPv4 so it quite easy to see why there is often strong views expressed about NAT!

MPLS and related QoS standards: The advent of MPLS covered in The rise and maturity of MPLS and MPLS and the limitations of the Internet addressed many of the needs of the IP community to be able to address Quality of Service issues by separating high-priority service traffic from low-priority traffic.

Round up

Don’t break what works. IP networks take a considerable amount of skill and hard work to keep alive. They always seem to be ‘living on the edge’ and break down when a network administrator gets distracted. Leave well alone is the mantra by many operational groups.

The benefits of upgrading to IPv6 have been considerably eroded by the advent of NAT and MPLS. Combine this with the lack of an overall management body who could force through a universal upgrade and the innate inertia of carriers and ISPs probably means that IPv6 will never achieve such a dominant position as its progenitor IPv4.

According to one overview of IPv6, which gets to the heart of the subject, “Although IPv6 is taking its sweet time to conquer the world, it’s now showing up in more and more places, so you may actually run into it one of these days.”

This is not to say that IPv6 is dead, rather it is being marginalised by only being run in closed networks (albeit some rather large networks). There is real benefit to the Internet being upgraded to IPv6 as every individual and every device connected to it could be assigned its own unique address as envisioned by the Founders of the Internet. The inability to do this severely constrains services and applications which are not able to clearly identify an individual on an on-going basis as is inherent in a telephone number. This clearly reflects badly on the Internet.

IPv6 is a victim of the success of the Internet and the ubiquity of IPv4 and will probably never replace IPv4 in the Internet in the foreseeable future (Maybe I should never say never!). I was once asked by a Cisco Fellow how IPv6 could be rolled out, after shrugging my shoulders and laughing I suggested that it needed a Bill Gates of the Internet to force through the change. That suggestion did not go down too well. Funnily enough, now that IPv6 is incorporated into Vista we could see the day when this happens. The only fly in the ointment is that Vista has the same problems and challenges as IPv6 in replacing XP – users are finally tiring of never-ending upgrades with little practical benefit.

Interesting times.


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