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Exposing 9 Myths About IPv6

Geoff Huston

This is a special two-part series article providing a distinct and critical perspective on Internet Protocol Version 6 (IPv6) and the underlying realities of its deployment. The first part gives a closer look at how IPv6 came about. This part exposes the myths.

Good as all this is, these attributes alone have not been enough so far to propel IPv6 into broad-scale deployment, and consequently there has been considerable enthusiasm to discover additional reasons to deploy IPv6. Unfortunately, most of these reasons fall into the category of myth, and in looking at IPv6 it is probably a good idea, as well as fair sport, to expose some of these myths as well.

1. "IPv6 Is More Secure"

A common claim is that IPv6 is more "secure" than IPv4. It is more accurate to indicate that IPv6 is no more or less secure than IPv4. Both IPv4 and IPv6 offer the potential to undertake secure transactions across the network, and both protocols are potentially highly capable in attempting to undertake highly secure transactions. Yes, the IPv6 specification includes as mandatory support for Authentication and Encapsulating Security Payload extension headers, but no, there is no "mandatory to use" sticker associated with these extension headers, and, like IPv4 IP Security (IPSec), it is left to the application and the user to determine whether to deploy security measures at the network transport level. So, to claim that IPv6 is somehow implicitly superior to IPv4 is an overly enthusiastic claim that falls into the category of "IPv6 myth."

Now I should qualify this, because there is a distinction between the protocol and its environment of deployment. In the case of IPv4, this protocol capability is compromised in many environments in the face of various forms of deployed active middleware such as NAT. It's too early to tell with IPv6, but the line of argument is that NAT-based active middleware has been deployed as a means of address extension, and in a IPv6 world such devices are no longer necessary, and will not be deployed. So perhaps one could say that IPv6 enables a path toward widespread peer-to-peer authentication and transport security at the protocol level, but whether the deployment models faithfully follow along such a path remains an open question.

2. "IPv6 Is Required for Mobility"

It is also claimed that only IPv6 supports mobility. If one is talking about a world of tens of billions of mobile devices, then the larger IPv6 address fields are entirely appropriate for such large-scale deployments. IPv6 includes a developing concept of stateless autoconfiguration and Neighbor Discovery mechanisms.

But if the claim is more about the technology to support mobility than the number of mobile devices, then this claim also falls short. The key issue with mobility is that mobility at a network layer requires the network to separate the functions of providing a unique identity for each connected device, and identifying the location within the network for each device.

As a device "moves" within the network its identity remains constant while its location is changing. IPv4 overloaded the semantics of an address to include both identity and locality within an address, and IPv6 did not alter this architectural decision. In this respect, IPv4 and IPv6 offer the same levels of support for mobility. Both protocols require an additional header field to support a decoupled network identity, commonly referred to as the "home address," and then concentrate on the manner of the way in which the home agent maintains a trustable and accurate copy of the mobile node or current location of the network. This topic remains the subject of activity within the IETF in both IPv4 and IPv6.

3. "IPv6 Is Better for Wireless Networks"

Mobility is often associated with wireless, and again there has been the claim that somehow IPv6 is better suited for wireless environments than IPv4. Again this is well in the realm of myth.

Wireless environments differ from wireline environments in numerous ways. One of the more critical differences is that a wireless environment may experience bursts of significant levels of bit error corruption, which in turn will lead to periods of non-congestion-based packet loss within the network. A TCP transport session is prone to interpreting such packet loss as being the outcome of network level congestion. The TCP response is not only retransmission of the corrupted packets, but also an unnecessary reduction of the sending rate at the same time. Neither IPv4 nor IPv6 have explicit signaling mechanisms to detect corruption-based packet loss, and in this respect the protocols are similarly equipped, or ill-equipped as in this case, to optimize the carriage efficiency and performance of a wireless communications subnet.

4. "IPv6 Offers Better QoS"

Another consistent assertion is that IPv6 offers "bundled" support for differentiated Quality of Service (QoS), whereas IPv4 does not. The justification for this claim often points to the 20-bit flow label in the IPv6 header as some kind of instant solution to QoS. This claim conveniently omits to note that the flow identification field in the IPv6 header still has no practical application in large-scale network environments. Both IPv4 and IPv6 support an 8-bit traffic class field, which includes the same 6-bit field for differentiated service code points, and both protocols offer the same fields to an Integrated Services packet classifier. From this perspective, QoS deployment issues are neither helped nor hindered by the use of IPv4 or IPv6. Here, again, it is a case of nothing has changed.

5. "Only IPv6 Supports Auto-Configuration"

Another common claim is that only IPv6 offers "plug-and-play" autoconfiguration. Again this is an overenthusiastic statement, given the widespread use of the Dynamic Host Configuration Protocol (DHCP) in IPv4 networks these days. Both protocol environments support some level of "plug-and-play" auto-configuration capability, and in this respect the situation is pretty much the same for both IPv4 and IPv6.

6. "IPv6 Solves Routing Scaling"

It would be good if IPv6 included some novel approach that solved, or even mitigated to some extent, the routing scaling issues. Unfortunately, this is simply not the case, and the same techniques of address aggregation using provider hierarchies apply as much to IPv6 as they do to IPv4. The complexity of routing is an expression of the product of the topology of the network, the policies used by routing entities, and the dynamic behavior of the network — not the protocol being routed. The larger address space does little to improve on capability to structure the address space in order to decrease the routing load. In this respect IPv6 does not make IP routing any easier, nor any more scalable.

7. "IPv6 Provides Better Support for Rapid Prefix Renumbering"

If provider-based addressing is to remain an aspect of the deployed IPv6 network, then one way to undertake provider switching for multihomed end networks is to allow rapid renumbering of a network common prefix. Again, it has been claimed that IPv6 offers the capability to undertake rapid renumbering within a network to switch to a new common address prefix. Again IPv6 performs no differently from IPv4 in this regard. As long as "rapid" refers to a period of hours or days, then yes, IPv4 and IPv6 both support "rapid" local renumbering. For a shorter time frame for "rapid," such as a few seconds or even a few milliseconds, this is not really the case.

8. "IPv6 Provides Better Support for Multihomed Sites"

This leads on to the more general claim that IPv6 supports multi-homing and dynamic provider selection. Again this is an optimistic claim, and the reality is a little more tempered. Multihoming is relatively easy if you are allowed to globally announce the network address prefix without recourse to any form of provider-based address aggregation. But this is a case of achieving a local objective at a common cost of the scalability of the entire global routing system, and this is not a supportable cost. The objective here is to support some form of multihoming of local networks where any incremental routing load is strictly limited in its radius of propagation. This remains an active area of consideration for the IETF and clear answers, in IPv4 or IPv6, are not available at present. So at best this claim is premature, and more likely the claim will again fall into the category of myth rather than firm reality.

9. "IPv4 Has Run Out of Addresses"

Again, this is in the category of myth rather than reality. Of the total IPv4 space, some 6 percent is reserved and another 6 percent is used for multicast. Forty-one percent of the space has already been allocated, and the remaining 37 percent (or some 1.5 billion addresses) is yet to be allocated. Prior to 1994, some 36 percent of the address space had been allocated. Since that time, and this includes the entire Internet boom period, a further 15 percent of the available address space was allocated. With a continuation of current policies it would appear that IPv4 address space will be available for many years yet.

So Why IPv6 Anyway?

The general observation is that IPv6 is not a "feature-based" revision of IPv4 — there is no outstanding capability of IPv6 that does not have a fully functional counterpart in IPv4. Nor is there a pressing urgency to deploy IPv6 because we are about to run out of available IPv4 address space in the next few months or even years within what we regard as the "conventional" Internet.

It would appear that the real drivers for network evolution lurk in the device world. We are seeing the various wireless technologies, ranging from Bluetooth for personal networking through the increasingly pervasive IEEE 802.11 "hot-spot" networking to the expectations arising from various forms of third-generation (3G) large radius services being combined with consumer devices, control systems, identification systems, and various other forms of embedded dedicated function devices. The silicon industry achieves its greatest advantage through sheer volume of production, and it is in the combination of Internet utility with the production volumes of the silicon industry that we will see demands for networking that encompasses tens, if not hundreds, of billions of devices. This is the world where IPv6 can and will come into its own, and I suspect that it is in this device and utility mode of communications that we will see the fundamental drivers that will lead to widespread deployment of IPv6 support networks.

Reprinted with permission from The Internet Protocol Journal (IPJ), Volume 6, No. 2, June, 2003. IPJ is a quarterly technical journal published by Cisco Systems.

By Geoff Huston, Author & Chief Scientist at APNIC. (The above views do not necessarily represent the views of the Asia Pacific Network Information Centre.)

Related topics: Internet Protocol, IPv6, Mobile, Security, Telecom

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