]> Independent

2386 Panoramic Circle Apopka Florida 32703 USA d3e3e3@gmail.com

Huawei Technologies

Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China jie.dong@huawei.com

Internet 6MAN Working Group IPv6 hop-by-hop options extension headers There are an increasing number of IPv6 hop-by-hop options specified but such IPv6 options are poorly handled, particularly by high-speed routers in the core Internet where packets having options may be discarded. This document proposes a simple method of transiently hiding such options for part of a packet's path to protect the packet from discard or mishandling.

Introduction As discussed in [Options3] there are an increasing number of IPv6 hop-by-hop options being specified. But such IPv6 options, are poorly handled, particularly by high-speed routers in the core Internet where packets having options may be discarded. This document proposes a simple method of transiently hiding such options for part of a packet's path to protect the packet from discard or mishandling. In this document, the network area where options are hidden is called the "opaque area".

Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Terms:

ASIC

- Application Specific Integrated Circuit.

field

- an area of one or more contiguous bits within a larger data structure.

opaque area

- The part of the IPv6 network within which options are hidden.

IP Options and Option Handling Problems This Section is informational and intended to provide background information. In the early days of the Internet, much of the traffic was text, transmission speeds were slow, and IP routers were commonly small general-purpose computers. Under these conditions, parsing IP headers with various options or combinations of options, handling variable length options, etc., was relatively easy. However, as time passed, the Internet increased in size, bandwidth grew including more voluminous media such as video, transmission speeds increased enormously, and latency/responsiveness requirements became more stringent. These requirements have led to IP routers, especially in the core of the Internet, becoming less flexible and more specialized. To be able to handle data faster and more efficiently, such core IP routers are divided into a forwarding plane and a control plane where the forwarding plane handles the usual data forwarding while the control plane handles routing control messages and other packets that the data plane cannot handle. In some IP routers, the forwarding plane is implemented with Application Specific Integrated Circuits (ASICs) that are inflexible and may need fields they examine in an IP packet header to be at a fixed offset from the beginning of the packet. Meanwhile, the control plane may be implemented through a general-purpose computer which can only handle a limited number of packets per unit time. For these reasons, many IP routers do not implement many, if any, types of IPv6 Hop-by-Hop options (or IPv4 header options) except through the control plane which has limited capacity. Sending packets with such options to the control plane can overwhelm the control plane and interfere with routing control messages or other critical functions. Very often, particularly for IP routers handling a large volume of traffic, a strategy is adopted of dropping IP packets with such header options or ignoring the header options. See for a further discussion of these option handling problems.

IPv6 Options Figure 1 shows the IPv6 header . The initial 4-bit Version field indicates the IP version number and would be 0b0110 to indicate the value 6.

IPv6 Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Traffic Class | Flow Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Length | Next Header | Hop Limit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Source Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Destination Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The value of the 8-bit Next Header field specifies the type and format of information immediately following the header. For example, a value of 17 in the Next Header field indicates that the header is immediately followed by a User Datagram Protocol (UDP) message and a value of 6 would indicate the header is followed by a Transmission Control Protocol (TCP) message. In some cases, the data immediately after the IPv6 header can be a header that itself includes a Next Header field for the type of data following it and so on as shown in Figure 2. Such headers, after the initial IPv6 header and before the main payload, are called Extension Headers and can be viewed as extensions to the IPv6 header. At this time specified extension headers include the six listed below, additional extension headers have been proposed, and likely more extension headers will be proposed and specified in the future. Specified extension headers:

• Hop-by-Hop Options
• Fragment
• Destination Options
• Routing
• Authentication
• Encapsulating Security Payload

In the two "options" types of extension header, the "Hop-by-Hop Options" and "Destination Options", the extension header content is further structured into options each of which, except for a one byte "pad1" option, is an 8-bit type followed by an 8-bit option length, followed by the option value. Hop-by-Hop options were initially specified to require that every router pay attention to them. While this has been relaxed in the most recent IPv6 specification, they are still sometimes viewed as imposing a burden on every IP router through which they pass.

IPv6 Option Extension Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Overview of the Protocol Figure 3 shows a simplified high-level view of a network path between two hosts within local networks through an opaque area. In reality there are likely to be more levels with a local network, whether a home, office, data center, or whatever. In the case where the opaque area is the Internet core, thses would usually be connected through one or more levels of lower tier service provider before connecting to a Tier 1 provider that connects to the core, also known as the default free zone.

High Level View of an Internet Path - - - - - - - - - - - - - - - - . . - - - - - - - - - - . Network 1 . . Opaque Area / . . . . Internet Core . . +------+ +---+ +---+ . . +---+ . . |Host A|---|R10|-...-|R19|------------------|R90| . . +------+ +---+ +---+ . . +---+ . . . . | | . . - - - - - - - - - - - - - - - - . ... . ..... . ....... . ....... - - - - - - - - - - - - - - - - . . ..... . Network 2 . . ... . . . | | . . +------+ +---+ +---+ . . +---+ . . |Host B|---|R20|-...-|R29|------------------|R99| . . +------+ +---+ +---+ . . +---+ . . . . . . - - - - - - - - - - - - - - - - - - - - - - - - - - .

There are efforts to improve and streamline handling of IPv6 Hop-by-Hop options such as the methods in and . However, even if such a method were popular and deployed in some network areas, there is likely to be significant delay before it would be deployed in most of the Internet core. While some Internet core routers may ignore options, others discard packets with options and, as long as there is a significant chance of such discard, options are rendered essentially useless on paths through the Internet core. A solution is to hide options in IP packets while they are in an area that does not properly handle options, such as the Internet core. This document specifies a protocol that does this hiding in an easily detectable and reversible fashion. Thus options can be easily unhidden on leaving the problematic area. IPv6 Hop-by-Hop options so hidden might not be effective but the situation can be an improvement over the traffic using such options being discarded. This solution requires destination support but that would be knowable in many cases such as traffic between branches of the same company or between a customer and a data center. To obtain more uniform handling of packets in a flow, it may be desirable to treat all packet in the flow as if they had such options in that the packet would be transformed to hide and unhide options even if there were none. Alternatively, this transformation could be applied to all packets starting with the first having a problematic option.

Transiently Hiding IPv6 Options IPv6 Hop-by-Hop options SHOULD be hidden on entry to an opaque area by replacing the zero Next Header field in the IPv6 Header by the opaque IP protocol number TBD. If this is not done, then the options will be exposed within the opaque area and may cause packet discard or other problems. Hiding is a very simple modification of one 8-bit field in a fixed location that has no effect of the size of the packet and leaves the Traffic Class, Flow Label, Hop Limit, etc., unchanged. They are unhidden by changing this opaque IP protocol number in the IPv6 header back to zero. The points of hiding and unhiding in the packet's path (or paths if multicast) should be chosen to maximize the routers at the beginning and end of the path (Figure 3) that implement the options while minimizing the chance of unwanted packet discard or other damaging behavior. Unhiding is likewise a very simple operation. IPv6 packets with options hidden are easily recognized by the Next Protocol field value of TBD in the IPv6 header. Hidden options MUST be unhidden on exit from the opaque area or subsequent routers or destination hosts may be presented with IPv6 packets whose Next Protocol field contains a value they are not programmed to handle. This might result in packet discard.

Evolution to Greater Option Support This solution supports the evolution of the Internet toward more widespread support or beneficent handling of hop-by-hop options as follows:

• As acceptable option handling is more widely implemented, probably starting at lower bandwidth routers nearer the edge, the boundaries at which options are hidden and unhidden to avoid problems in the Internet core can migrate closer to the core.
• If scattered core routers improve to provide acceptable option handling, they can recognize the opaque protocol number and perform options, perhaps in a limited way, on packets where those options are hidden to unimproved routers.

IANA Considerations IANA is requested to assign a number from the "Assigned Internet Protocol Numbers" registry as follows:

Decimal	Keyword	Protocol	IPv6 Ex Hdr	Reference
TBD	Opaque	Opaque		[this document]

Security Considerations The use of the opaque IP Protocol to mask options is intended to disable normal analysis of the following packet content, specifically hop-by-hop options in the IPv6 header. This would make firewalls, deep packet analysis, and the like less effective. However, such methods are less likely to be present in the Internet core where packets are the most likely to be obscured. Furthermore, firewalls tend to only admit packets with known permissible values in protocol header fields such as the IP protocol field. The rejection by a firewall of a packet with the opaque IP protocol value will protect the nodes behind that firewall from possible damage due to the receipt of a packet modified as specified in this document. If the firewall does know the opaque IP Protocol value, it should be configured to treat packets with that value safely, possibly by reversing the option hiding transformation. Performing the specified option hiding header modification only for packets with options would reveal which packets have that characteristic and might cause re-ordering of those packets with respect to other packets in the same flow. Thus, it may be beneficial to perform the specified modification on all packets in an order sensitive flow. Should an IPv6 packet modified to hide options get through to a host that does not understand this modification, it would almost certainly be discarded due to having an unknown IP Protocol. This might disrupt that communication but should not cause security problems.

Normative References Informative References Huawei Technologies

lizhenbin@huawei.com

Huawei Technologies

pengshuping@huawei.com

Verizon Inc.

gyan.s.mishra@verizon.com

Check Point Software

959 Skyway Road San Carlos CA 94070 USA bob.hinden@gmail.com

University of Aberdeen

School of Engineering Fraser Noble Building Aberdeen AB24 3UE UK gorry@erg.abdn.ac.uk

Huawei Technologies

lizhenbin@huawei.com

Huawei Technologies China Telecom

China xiechf@chinatelecom.cn

China Unicom

Beijing China qinzhuangzhuang@chinaunicom.cn

Verizon Inc.

USA gyan.s.mishra@verizon.com

Revision History RFC Editor: Please delete this appendix before publication.

-00 to -01 Minor editorial changes. Add more Security Considerations. Add Acknowledgements section.

-01 to -02 Delete IPv4 material. It was a bit complex and almost no one really cares about IPv4 options. Also, minor editorial changes.

-02 to -03 to -04 Minor changes.

-04 to -05 Convert to XMLv3. Add author.

-05 to -07 Minor changes.

-07 to -10 Keep alive.

-10 to -11

• Greatly expand Security Considerations section.
• Add wording.
• Generalize to "opaque area" as well as Internet core.
• Editorial improvements and typo fixes.

Acknowledgments The helpful comments of the following are gratefully acknowledged: Peng Shuping