--- 1/draft-ietf-6man-flow-3697bis-04.txt 2011-06-29 22:15:55.000000000 +0200 +++ 2/draft-ietf-6man-flow-3697bis-05.txt 2011-06-29 22:15:55.000000000 +0200 @@ -1,23 +1,23 @@ 6MAN S. Amante Internet-Draft Level 3 Obsoletes: 3697 (if approved) B. Carpenter Updates: 2205, 2460 (if approved) Univ. of Auckland Intended status: Standards Track S. Jiang -Expires: November 12, 2011 Huawei Technologies Co., Ltd +Expires: December 31, 2011 Huawei Technologies Co., Ltd J. Rajahalme Nokia Siemens Networks - May 11, 2011 + June 29, 2011 IPv6 Flow Label Specification - draft-ietf-6man-flow-3697bis-04 + draft-ietf-6man-flow-3697bis-05 Abstract This document specifies the IPv6 Flow Label field and the minimum requirements for IPv6 nodes labeling flows, IPv6 nodes forwarding labeled packets, and flow state establishment methods. Even when mentioned as examples of possible uses of the flow labeling, more detailed requirements for specific use cases are out of scope for this document. @@ -33,21 +33,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on November 12, 2011. + This Internet-Draft will expire on December 31, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -70,32 +70,32 @@ than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. IPv6 Flow Label Specification . . . . . . . . . . . . . . . . 5 3. Flow Labeling Requirements in the Stateless Scenario . . . . . 6 4. Flow State Establishment Requirements . . . . . . . . . . . . 8 5. Essential correction to RFC 2205 . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 - 6.1. Covert Channel Risk . . . . . . . . . . . . . . . . . . . 8 + 6.1. Covert Channel Risk . . . . . . . . . . . . . . . . . . . 9 6.2. Theft and Denial of Service . . . . . . . . . . . . . . . 9 - 6.3. IPsec and Tunneling Interactions . . . . . . . . . . . . . 10 + 6.3. IPsec and Tunneling Interactions . . . . . . . . . . . . . 11 6.4. Security Filtering Interactions . . . . . . . . . . . . . 11 - 7. Differences from RFC 3697 . . . . . . . . . . . . . . . . . . 11 + 7. Differences from RFC 3697 . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 - 10. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 12 + 10. Change log [RFC Editor: Please remove] . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . . 13 - 11.2. Informative References . . . . . . . . . . . . . . . . . . 13 - Appendix A. Simple 20-bit Hash Function . . . . . . . . . . . . . 14 + 11.2. Informative References . . . . . . . . . . . . . . . . . . 14 + Appendix A. Example 20-bit Hash Function . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction From the viewpoint of the network layer, a flow is a sequence of packets sent from a particular source to a particular unicast, anycast, or multicast destination that a node desires to label as a flow. From an upper layer viewpoint, a flow could consist of all packets in a specific transport connection or a media stream. However, a flow is not necessarily 1:1 mapped to a transport @@ -220,40 +220,43 @@ 3. Flow Labeling Requirements in the Stateless Scenario This section defines the minimum requirements for methods of setting the flow label value within the stateless scenario of flow label usage. To enable Flow Label based classification, source nodes SHOULD assign each unrelated transport connection and application data stream to a new flow. A typical definition of a flow for this purpose is any set of packets carrying the same 5-tuple {dest addr, source addr, - protocol, dest port, source port}. + protocol, dest port, source port}. It should be noted that a source + node always has convenient and efficient access to this 5-tuple, + which is not always the case for nodes that subsequently forward the + packet. It is desirable that flow label values should be uniformly distributed to assist load distribution. It is therefore RECOMMENDED that source hosts support the flow label by setting the flow label field for all packets of a given flow to the same value chosen from an approximation to a discrete uniform distribution. Both stateful and stateless methods of assigning a value could be used, but it is outside the scope of this specification to mandate an algorithm. The algorithm SHOULD ensure that the resulting flow label values are unique with high probability. However, if two simultaneous flows are by chance assigned the same flow label value, and have the same source and destination addresses, it simply means that they will receive the same treatment throughout the network. As long as this is a low probability event, it will not significantly affect load distribution. A possible stateless algorithm is to use a suitable 20 bit hash of - values from the IP packet's 5-tuple. A simple hash function is - described in Appendix A. + values from the IP packet's 5-tuple. A simple example hash function + is described in Appendix A. An alternative approach is to to use a pseudo-random number generator to assign a flow label value for a given transport session; such a method will require minimal local state to be kept at the source node, by recording the flow label associated with each transport socket. Viewed externally, either of these approaches will produce values that appear to be uniformly distributed and pseudo-random. @@ -262,35 +265,53 @@ guess the next value. A source node which does not otherwise set the flow label MUST set its value to zero. A node that forwards a flow whose flow label value in arriving packets is zero MAY change the flow label value. In that case, it is RECOMMENDED that the forwarding node sets the flow label field for a flow to a uniformly distributed value as just described for source nodes. + o The same considerations apply as to source hosts setting the flow - label; in particular, the normal case is that a flow is defined by - the 5-tuple. - o This option, if implemented, would presumably be used by first-hop - or ingress routers. It might place a considerable per-packet - processing load on them, even if they adopted a stateless method - of flow identification and label assignment. This is why the - principal recommendation is that the source host should set the - label. + label; in particular, the preferred case is that a flow is defined + by the 5-tuple. However, there are cases in which the complete + 5-tuple for all packets is not readily available to a forwarding + node, in particular for fragmented packets. In such cases a flow + can be defined by fewer IPv6 header fields, typically using only + the 2-tuple {dest addr, source addr}. There are alternative + approaches that implementers could choose, such as: + + * A forwarding node might use the 5-tuple to define a flow + whenever possible, but use the 2-tuple when the complete + 5-tuple is not available. In this case, unfragmented and + fragmented packets belonging to the same transport session + would receive different flow label values, altering the effect + of subsequent load distribution based on the flow label. + * A forwarding node might use the 2-tuple to define a flow in all + cases. In this case, subsequent load distribution would be + based only on IP addresses. + o This option, if implemented, would presumably be of value in + first-hop or ingress routers. It might place a considerable per- + packet processing load on them, even if they adopted a stateless + method of flow identification and label assignment. However, it + will not interfere with host-to-router load sharing [RFC4311]. + Therefore, it needs to be under the control of network managers, + to avoid unwanted processing load and any other undesirable + effects. For this reason it MUST be a configurable option, + disabled by default. The preceding rules taken together allow a given network to include routers that set flow labels on behalf of hosts that do not do so. - - They also recommend that flow labels exported to the Internet are - always either zero or uniformly distributed. + The complications described explain why the principal recommendation + is that the source hosts should set the label. 4. Flow State Establishment Requirements A node that sets the flow label MAY also take part in a flow state establishment method that results in assigning specific treatments to specific flows, possibly including signaling. Any such method MUST NOT disturb nodes taking part in the stateless scenario just described. Thus, any node that sets flow label values according to a stateful scheme MUST choose labels that conform to Section 3 of the present specification. Further details are not discussed in this @@ -467,41 +488,46 @@ firewalls. For further details see [I-D.ietf-6man-flow-update]. 8. IANA Considerations This document requests no action by IANA. 9. Acknowledgements - Valuable comments and contributions were made by Ran Atkinson, Fred - Baker, Steve Blake, Remi Despres, Alan Ford, Fernando Gont, Brian - Haberman, Tony Hain, Joel Halpern, Qinwen Hu, Chris Morrow, Thomas - Narten, Mark Smith, Pascal Thubert, Iljitsch van Beijnum, and other - participants in the 6man working group. + Valuable comments and contributions were made by Jari Arkko, Ran + Atkinson, Fred Baker, Steve Blake, Remi Despres, Alan Ford, Fernando + Gont, Brian Haberman, Tony Hain, Joel Halpern, Qinwen Hu, Chris + Morrow, Thomas Narten, Mark Smith, Pascal Thubert, Iljitsch van + Beijnum, and other participants in the 6man working group. Cristian Calude suggested the von Neumann algorithm in Appendix A. + David Malone and Donald Eastlake gave additional input about hash + algorithms. Steve Deering and Alex Conta were co-authors of RFC 3697, on which this document is based. Contributors to the original development of RFC 3697 included Ran Atkinson, Steve Blake, Jim Bound, Francis Dupont, Robert Elz, Tony Hain, Robert Hancock, Bob Hinden, Christian Huitema, Frank Kastenholz, Thomas Narten, Charles Perkins, Pekka Savola, Hesham Soliman, Michael Thomas, Margaret Wasserman, and Alex Zinin. This document was produced using the xml2rfc tool [RFC2629]. 10. Change log [RFC Editor: Please remove] + draft-ietf-6man-flow-3697bis-05: resolved AD comments, improved hash + algorithm, 2011-06-29. + draft-ietf-6man-flow-3697bis-04: update to resolve further WG comments, 2011-05-11: o Suggested a specific hash algorithm to generate a flow label. o Removed reference to stateful domain. o Added text about covert channel and tuned text about firewall behavior; removed the confusing word "immutable". o Added that Section 6 of RFC 2460 is replaced. o Editorial fixes. draft-ietf-6man-flow-3697bis-03: update to resolve WGLC comments, @@ -548,21 +573,21 @@ 11.2. Informative References [I-D.gont-6man-flowlabel-security] Gont, F., "Security Assessment of the IPv6 Flow Label", draft-gont-6man-flowlabel-security-01 (work in progress), November 2010. [I-D.ietf-6man-flow-update] Amante, S., Carpenter, B., and S. Jiang, "Rationale for update to the IPv6 flow label specification", - draft-ietf-6man-flow-update-05 (work in progress), + draft-ietf-6man-flow-update-06 (work in progress), May 2011. [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June 1999. [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, @@ -570,59 +595,71 @@ [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. + [RFC4311] Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load + Sharing", RFC 4311, November 2005. + [vonNeumann] von Neumann, J., "Various techniques used in connection with random digits", National Bureau of Standards Applied Math Series 12, 36-38, 1951. -Appendix A. Simple 20-bit Hash Function +Appendix A. Example 20-bit Hash Function As mentioned in Section 3, a stateless hash function may be used to - generate a flow label value from an IPv6 packet's 5-tuple. An - example function, based on an algorithm by von Neumann known to - produce an approximately uniform distribution [vonNeumann], is as - follows: + generate a flow label value from an IPv6 packet's 5-tuple. It is not + trivial to choose a suitable hash function, and it is expected that + extensive practical experience will be required to identify the best + choices. An example function, based on an algorithm by von Neumann + known to produce an approximately uniform distribution [vonNeumann], + follows. For each packet for which a flow label must be generated, + execute the following steps: 1. Split the destination and source addresses into two 64 bit values each, thus transforming the 5-tuple into a 7-tuple. - 2. Add the seven components together using unsigned 64 bit - arithmetic, discarding any carry bits. + 2. Add the following five components together using unsigned 64 bit + arithmetic, discarding any carry bits: both parts of the source + address, both parts of the destination address, and the protocol + number. 3. Apply the von Neumann algorithm to the resulting string of 64 bits: 1. Starting at the least significant end, select two bits. 2. If the two bits are 00 or 11, discard them. 3. If the two bits are 01, output a 0 bit. 4. If the two bits are 10, output a 1 bit. 5. Repeat with the next two bits in the input 64 bit string. - 6. Stop when 20 bits have been output (or when the 64 bit string + 6. Stop when 16 bits have been output (or when the 64 bit string is exhausted). - 4. In the highly unlikely event that the result is exactly zero, set + 4. Add the two port numbers to the resulting 16 bit number. + 5. Shift the resulting value 4 bits left and mask with 0xfffff. + 6. In the highly unlikely event that the result is exactly zero, set the flow label arbitrarily to the value 1. + Note that this simple example does not include any form of + obfuscation. + Authors' Addresses Shane Amante Level 3 Communications, LLC 1025 Eldorado Blvd Broomfield, CO 80021 USA Email: shane@level3.net - Brian Carpenter Department of Computer Science University of Auckland PB 92019 Auckland, 1142 New Zealand Email: brian.e.carpenter@gmail.com Sheng Jiang