Non-Managed IPv6 Tunnels considered Harmful

Abstract

IPv6 is ongoing and natively being deployed by a growing community and it is important that the quality perception and traffic flows are as optimal as possible. Ideally it would be as good as the IPv4 perceptive experience.

This paper looks into a set of transitional technologies where the actual user has IPv6 connectivity through the means of IPv6-in-IPv4 tunnels. A subset of the available tunnels has the property of being non-managed (i.e. 6to4 [RFC3056] (Carpenter, B. and K. Moore, “Connection of IPv6 Domains via IPv4 Clouds,” February 2001.) and Teredo [RFC4380] (Huitema, C., “Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs),” February 2006.) ).

While native IPv6 deployments will keep growing it is uncertain or even expected that non-managed IPv6 tunnels will be providing the same user experience and operational quality as managed tunnels or native IPv6 connectivity.

This paper will detail some considerations around non-managed tunnels and will document the harmful element of these for the future growth of networks and the Internet.

Status of this Memo

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This Internet-Draft will expire on March 4, 2011.

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Table of Contents

1.  Introduction
2.  Managed Tunnelling Properties
3.  Tunnel User Experience Views
4.  Why do non-managed tunnels exist?
5.  Non-Managed Tunnelling Properties
    5.1.  Performance
    5.2.  Topological Considerations
    5.3.  Operational Provisioning
    5.4.  Operational Troubleshooting
    5.5.  Security
    5.6.  Content Services
6.  Conclusion
7.  IANA Considerations
8.  Security Considerations
9.  Acknowledgements
10.  References
    10.1.  Normative References
    10.2.  Informative References
§  Authors' Addresses

1.  Introduction

While the Internet and networks continue to grow, it is found that the deployment of IPv6 within these networks is an ongoing activity due to global IPv4 address pool depletion. An important aspect is that the quality, availability and security of the IPv6 connectivity is as good as possible, and when possible even more advanced as the IPv4 connectivity.

Historically IETF has been facilitating a variety of technologies and procedures to deploy IPv6 successfully in addition to existing IPv4 connectivity. In general and for the sake of this draft these procedures and technologies can be divided into three major groups: (1) native (dual-stack) IPv6, (2) Tunnelled IPv6 and (3) Translation. While native IPv6 deployments has been steadily growing, the value and the drawbacks of some tunnelling mechanisms can be investigated. Translational techniques provide a total different aspect of considerations and applicability and is beyond the scope of this paper. Transition techniques have been and still are in many cases important for the bootstrapping of IPv6, this paper will look into a range of property aspects of non-managed IPv6 tunnelling techniques. Areas of perverse traffic paths, security considerations, lack of business incentives to run tunnel relays/gateways, black holing and ownership of supportability will be analysed. Finally the paper will conclude that for the growth of IP connectivity, non-managed tunnelling techniques are considered harmful especially for those that want to access applications over the network through pervasive IPv6 connectivityand have no particular interrest on how connectivity to the applications is established (IPv4, translation, IPv6, etc...)

2.  Managed Tunnelling Properties

A managed tunnel is a tunnel has a few properties supporting the ownership and quality of the tunnel.

When using a managed service, there tends to be an administrative entity which provides quality assurance and can take action if users of the service are experiencing a degraded service. An example would be 6rd tunnels [RFC5969] (Townsley, W. and O. Troan, “IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification,” August 2010.)

In addition there is a general trust awareness and agreement between the user of the managed tunnel service and the provider of the managed tunnel service.

3.  Tunnel User Experience Views

The tunnel experience can be divided into three distinct segments: (1) the End-user view, (2) the Enterprise View and (3) the Service Provider View.

The End-user view exists mainly out of two different user profiles. The technical power user and the general user mainly trying to reach their favourite application on the network. The technical power user may have a particular interrest to run IPv6 as a transport mechanism, and if his upstream service provider has no native IPv6 connectivity available, then non-managed tunneling mechanisms may provide a solution satisfying to the immediate needs of the technical power user. Alternatively, the general user trying to reach his favourite network application, may have no interest or awareness of his IPv6 usage, particulary when non-managed tunnels are utilized.

The Enterprise View is a more traffic flows and network oriented possitioning. When the upstream service provider does not have an IPv6 offer, then the enterprise may start to rely upon a technology as 6to4 [RFC3056] (Carpenter, B. and K. Moore, “Connection of IPv6 Domains via IPv4 Clouds,” February 2001.). However this technology has the potential of creating quite perverse traffic paths when user want to reach applications on the Internet. When user would like to reach other 6to4 [RFC3056] (Carpenter, B. and K. Moore, “Connection of IPv6 Domains via IPv4 Clouds,” February 2001.) users, then more optimized traffic paths, generally following the IPv4 traffic paths are realized

The final view is how a Internet service provider looks into non-managed tunnel usage. A service provider may decide to deploy a 6to4 relay to increase the IPv6 quality of their customers. This a service which require resources (money, maintenance, etc...). Often the 6to4 relay service is not just (always) restricted to only the service providers customers, which as result provides often results in a demotivation to provide quality tunnel relay devices. From a content service provider perspective the usage of non-managed tunnel often results in measurable differences in RTT and reliability in some cases, and hence are reluctant to bring all services to mainstream IPv6 for all users 'just yet'.

4.  Why do non-managed tunnels exist?

Non-managed tunnels exist due to a variety of reasons.

Early adopters: people and organisations with a desire to use new and potentially market disrupting technologies and applications may have a desire to use the latest IP even when the upstream provider doesn't have an available service offering.

Lock-step process to implement IPv6: It is not trivial to move a system or an organisation in lock-step towards IPv6 and the aid of tunnels help in this process.

The utilisation of tunnels aid in providing a de-coupling between infrastructure readiness and application readiness, and hence contribute to the development of both elements.

5.  Non-Managed Tunnelling Properties

The properties of Non-managed tunnels span many different areas. In this section the properties are analysed and segmented within different areas of impact. In each case the comparison is made between native IPv6 connectivity and connectivity through a non-managed tunnel. A common property of non-managed tunnels is that they often use well-known anycast addresses or other well known addresses and anticipate upon the goodwill of middleware (typically a relay or gateway) device to serve as a tunnel termination point. In some cases, for example a 6to4 relay can be provided by a connected responsible service provider, and hence good quality operation can be guaranteed.

Non-managed tunnels often have asymmetric behaviour. There is an outbound and an inbound connectivity behaviour from the tunnel initiator. It is possible to influence the good quality tunnel behaviour of the outbound connectivity (e.g. by explicit setting of the 6to4 relay), however, influencing good inbound connectivity is often an issue.

5.1.  Performance

Deploying a tunnelling mechanism mostly results in encapsulation and de-capsulation efforts. Often this activity has a performance impact on the device, especially when the device does not use hardware acceleration for this functionality. If the performance impact is scoped into the device its lifetime through performance capacity management then the actual impact is predictive. Non-deterministic tunnels tend to have a non-predictive behaviour for capacity, and hence application and network performance is non-predictive. The key reason for this is the decoupling of the capacity management of the tunnel aggregation devices from the capacity desired by users of the aggregation devices.

During initial IPv6 deployment there have been mainly technical savvy people that have been using non-managed tunnel technologies and it has for many been working well. However, if non-managed tunnelling would be deployed in mass and especially when enabled by default by CPE vendors or host vendors then those aggregation points could become overloaded and result in bad performance. There are a few measures that can be taken, i.e. upgrade the CPU power of the aggregation device or its bandwidth available, however this may not happen without the right motivation for the operator of the aggregation device (i.e. cash flows, reputation, competitive reasons, etc... ).

5.2.  Topological Considerations

Due to non-managed IPv6 tunnels the traffic flows may result in sub-optimal flows through the network topology between two communicating devices. The impact for example can cause increase of the RTT and packet loss, especially considering the availability (or better non-availability) of tunnel aggregation/de-aggregation points of certain topological areas or realms. The increase of non-managed tunnel usage would amplify the negative impact on good quality connectivity. For many operators of tunnel aggregation/de-aggregation devices there is little motivation to increase the quality and number of available devices within a topological area or logistical realm.

5.3.  Operational Provisioning

Some elements regarding provisioning of both managed and non-managed tunnels can be controlled, while others are beyond control or influence of people and applications using tunnels. To make applications highly reliable and performing, all elements within the traffic path must provide an expected quality service and performance. For managed tunnels, the user or provider of the tunnel can exercise a degree of operational management and hence influence good quality behaviour upon the tunnel especially upon the aggregation and de-aggregation devices. In some cases even the traffic path between both aggregation and de-aggregation can be controlled. Non-managed tunnels however have less good quality behaviour of both tunnel aggregation and de-aggregation devices because often good quality behaviour is beyond the control or influence of the tunnel user. For non-managed tunnels the tunnel aggregator and/or tunnel de-aggregator are operated by a 3rd party which may have a conflicting interest with the user of the non-managed tunnel. An exception is where the use of the tunnel mechanism is all within one ISP, or ISPs who are 'well coupled', e.g. as happens between many NRENs.

5.4.  Operational Troubleshooting

When one is using non-managed tunnels, then these tunnels may get aggregated or de-aggregated by a 3rd party or a device outside the control of a contracted service provider. Troubleshooting these devices these devices will be pretty hard for the tunnel user or to work around the issue.

Also some tools like traceroute don't work too well on asymmetric paths. Another aspect is that tunnels show as one hop in a traceroute, not indicating where problems may be.

5.5.  Security

For an aggregating or de-aggregating tunnel device it is a non-trivial issue to separate the valid traffic from non-valid traffic because it is from the aggregation device perspective almost impossible to know -from- and -towards- about the tunnel traffic. This imposes potential attacks on the available resources of the aggregating/de-aggregating router. A detailed security analysis for 6to4 tunnels can be found in [RFC3964] (Savola, P. and C. Patel, “Security Considerations for 6to4,” December 2004.).

For the user of the non-managed IPv6 tunnel there is an underlying trust that the aggregating/de-aggregating device is a trustworthy device. However, some of the devices used are run by anonymous 3rd parties outside the trusted infrastructure from the user perspective, which is not an ideal situation. The usage of non-managed tunnels increases the risk of rogue aggregation/de-aggregation devices and may be open to malicious packet analyses or manipulation.

From the operator perspective, managing the aggregating/de-aggregating tunnel device, there is a trust assumption that no-one abuses the service. Abuse may impact preset or assumed service quality levels, and hence the quality provided can be impacted

There is also an impact caused by ipv4 firewalling upon non-managed tunnels. Common firewall policies recommend to block tunnels, especially non-managed tunnels, because there is no trust that the traffic within the tunnel is not of mallicious intend. This restricts the applicability of some non-managed tunnel mechanisms (e.g. 6to4). Other tunnel mechanisms have found manners to avoid traditional firewall filtering (e.g. Teredo) and open the local network infrastructure for mallicious influence (e.g. virus, worms, infrastructure attacs, etc..).

5.6.  Content Services

When providing content services a very important related aspect is that these services are accessible with high reliability, are trustworthy and have a high performance. Using non-managed tunnels makes this a much harder equation and can result in all three elements to suffer negatively, without the ability to uniquely identify and resolve the root cause. The statistical impact of non-mnaged tunnels has been measured by some Internet Content providers and is often an additional delay of O(100msec) (need to add reference here)

This reduces the interest of content providers to provide content services over IPv6 when non-managed tunnels are used.

6.  Conclusion

Non-managed tunnels have properties impacting the growth of networks and the Internet in a negative way. Consequences regarding black-holing, perverse traffic paths, lack of business incentive and operational management influence and security issues are a real pragmatic concern, while universal supportability for the tunnel relay services appear to be non-trivial. Due to these elements the usage of non-managed tunnelling can be considered harmful for the growth of networks and the Internet.

7.  IANA Considerations

There are no extra IANA consideration for this document.

8.  Security Considerations

There are no extra Security consideration for this document.

9.  Acknowledgements

10.  References

10.1. Normative References

10.2. Informative References

Authors' Addresses