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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) == Outdated reference: draft-ietf-roll-terminology has been published as RFC 7102 == Outdated reference: A later version (-02) exists of draft-thubert-roll-forwarding-frags-00 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco 4 Intended status: Standards Track May 9, 2012 5 Expires: November 10, 2012 7 Use of the IPv6 Flow Label within an LLN 8 draft-thubert-roll-flow-label-01 10 Abstract 12 This document present how the Flow Label can be used inside a LLN as 13 a replacement to the RPL option and provides rules for the root to 14 set and reset the Flow Label when forwarding between the inside of 15 RPL domain and the larger Internet, in both direction. This new 16 operation aims at saving an IPv6 in IPv6 encapsulation within the RPL 17 domain that is required with the RPL option for all packets that 18 reach outside of the RPL domain. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on November 10, 2012. 37 Copyright Notice 39 Copyright (c) 2012 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5 56 3. Flow Label Format Within the RPL Domain . . . . . . . . . . . . 5 57 4. Root Operation . . . . . . . . . . . . . . . . . . . . . . . . 6 58 4.1. Incoming Packets . . . . . . . . . . . . . . . . . . . . . 6 59 4.2. Outgoing Packets . . . . . . . . . . . . . . . . . . . . . 6 60 5. RPL node Operation . . . . . . . . . . . . . . . . . . . . . . 7 61 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 62 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 63 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7 64 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 66 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 67 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 1. Introduction 71 In some Low Power and Lossy Network (LLN) applications such as 72 control systems [RFC5673], a packet loss is usually acceptable but 73 jitter and latency must be strictly controlled as they can play a 74 critical role in the interpretation of the measured information. 75 Sensory systems are often distributed, and the control information 76 can in fact be originated from multiple sources and aggregated. As a 77 result, it can be a requirement for related measurements from 78 multiple sources to be treated as a single flow following a same path 79 over the Internet in order to experience similar jitter and latency. 80 The traditional tuple of source, destination and ports might then not 81 be the proper indication to isolate a meaningful flow. 83 In a typical LLN application, the bulk of the traffic consists of 84 small chunks of data (in the order few bytes to a few tens of bytes) 85 at a time. In the industrial case, a typical frequency is 4Hz but it 86 can be a lot slower than that for, say, environmental monitoring. 87 The granularity of traffic from a single source is too small to make 88 a lot of sense in load balancing application. 90 In such cases, related packets from multiple sources should not be 91 load-balanced along their path in the Internet; load-balancing can be 92 discouraged by tagging those packets with a same Flow Label in the 93 IPv6 [RFC2460] header. This can be achieved if the Flow Label in 94 packets outgoing a RPL domain are set by the root of the RPL 95 structure as opposed to the actual source. It derives that the Flow 96 Label could be reused inside the RPL domain. 98 The Routing Protocol for Low Power and Lossy Networks (RPL) [RFC6550] 99 specification defines a generic Distance Vector protocol that is 100 adapted to a variety of LLNs. RPL forms Destination Oriented 101 Directed Acyclic Graphs (DODAGs) which root often acts as the Border 102 Router to connect the RPL domain to the Internet. The root is 103 responsible to select the RPL Instance that is used to forward a 104 packet coming from the Internet into the RPL domain. 106 A classical RPL implementation will use the RPL Option for Carrying 107 RPL Information in Data-Plane Datagrams [RFC6553] to tag a packet 108 with the Instance ID and other information that RPL requires for its 109 operation within the RPL domain. Sadly, the Option must be placed in 110 a Hop-by-Hop header that must be added to or removed from packets 111 that cross the border of the RPL domain. For reasons such as the 112 capability to send ICMP errors, back, this operation involves an 113 extra 6in6 encapsulation within the RPL domain that is detrimental to 114 the LLN operation, in particular with regards to bandwidth and 115 battery constraints. The extra encapsulation may cause a containing 116 frame to grow above maximum frame size, leading to Layer 2 or 6LoWPAN 118 [RFC4944] fragmentation, which in turn cause even more energy 119 spending and issues discussed in the LLN Fragment Forwarding and 120 Recovery [I-D.thubert-roll-forwarding-frags]. 122 ------+--------- 123 | Internet | 124 | | Native IPv6 125 +-----+ | 126 | | Border Router (RPL Root) | 127 | | || | || 128 +-----+ || | || IPv6 + 129 | || | || HbH 130 o o o o || | || headers 131 o o o o o o o o o || | || 132 o o o o o o o o o o || | || 133 o o o o o o o o o || | || 134 o o o o o o o o 135 o o o o o o 136 o o o o 138 LLN 140 Figure 1: 6in6 Encapsulation within the LLN 142 Additionally, Compression Format for IPv6 Datagrams over IEEE 143 802.15.4-Based Networks [RFC6282] and its variants for other types of 144 LLNs do not provide an efficient compression for the RPL option so 145 the cost in current implementations can not be alleviated in any 146 fashion. So even for packets that are confined within the RPL domain 147 and do not need the 6in6 encapsulation, the use of the flow label 148 instead of the RPL option is a valuable saving. 150 All the packets that are leaving a DODAG of a RPL domain towards the 151 Internet will transit via a same root. The root is an ideal place to 152 set the IPv6 Flow Label to a same value across multiple sources of a 153 same flow when that operation is needed, ensuring complience with the 154 rules defined by the IPv6 Flow Label Specification [RFC6437] within 155 the Internet. At the same time, the root segragates the Internet and 156 the RPL domain, allowing to reuse the Flow Label within the RPL 157 domain. 159 In a LLN, each transmitted bit represents energy and each saving 160 counts. So comsuming 20 bits as recommended in the stateless usage 161 of the Flow Label by [RFC6437] to transport a randomized value will 162 not be very popular. On the other hand, it makes sense to recommend 163 the computation of a stateless Flow Label at the root of the LLN 164 towards the Internet. 166 It can be noted that [RFC6282] provides an efficient header 167 compression for packets that do have the Flow Label set in the IPv6 168 header. It results that the same information as transported in the 169 RPL option itself represents actually less bits in the air when the 170 Flow Label is used instead. This document specifies how the Flow 171 Label can be reused within the RPL domain as a replacement to the RPL 172 option. The use of the Flow Label within a RPL domain is an instance 173 of the stateful scenarios as discussed in [RFC6437] where the states 174 include the rank of a node and the RPLInstanceID that identifies the 175 routing topology. 177 2. Terminology 179 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 180 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 181 document are to be interpreted as described in [RFC2119]. 183 The Terminology used in this document is consistent with and 184 incorporates that described in `Terminology in Low power And Lossy 185 Networks' [I-D.ietf-roll-terminology] and [RFC6550]. 187 3. Flow Label Format Within the RPL Domain 189 [RFC6550] section 11.2 specifies the fields that are to be placed 190 into the packets for the purpose of Instance Identification, as well 191 as Loop Avoidance and Detection. Those fields include an 'O', and 192 'R' and an 'F' bits, the 8-bit RPLInstanceID, and the 16-bit 193 SenderRank. SenderRank is the result of the DAGRank operation on the 194 rank of the sender, where the DAGRank operation is defined in section 195 3.5.1 as: 197 DAGRank(rank) = floor(rank/MinHopRankIncrease) 199 If MinHopRankIncrease is set to a multiple of 256, it appears that 200 the most significant 8 bits of the SenderRank will be all zeroes and 201 could be ommitted. In that case, the Flow Label MAY be used as a 202 replacement to the [RFC6553] RPL option. To achive this, the 203 SenderRank is expressed with 8 least significant bits, and the 204 information carried within the Flow Label in a packet is constructed 205 follows: 207 0 1 2 208 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 210 | |O|R|F| SenderRank | RPLInstanceID | 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 Figure 1: The RPL Flow Label 215 The first (leftmost) bit of the Flow Label is reserved and should be 216 set to zero. 218 4. Root Operation 220 [RFC6437] section 3 intentionally does not consider flow label values 221 in which any of the bits have semantic significance. However, the 222 present specification assigns semantics to various bits in the flow 223 label, destroying within the edge network that is the RPL domaina 224 property of belonging to a statistically uniform distribution that is 225 desirable in the rest of the Internet. This property MUST be 226 restored by the root for outgoing packets. 228 It can be noted that the rationale for the statistically uniform 229 distribution does not necessarily bring a lot of value within the RPL 230 domain. In a specific use case where it would, that value must be 231 compared with that of the battery savings in order to decide which 232 technique the deployment will use to transport the RPL information. 234 4.1. Incoming Packets 236 When routing a packet towards the RPL domain, the root applies a 237 policy to determine whether the Flow Label is to be used to carry the 238 RPL information. If so, the root MUST reset the Flow Label and then 239 it MUST set all the fields in the Flow Label as prescribed by 240 [RFC6553] using the format specified in Figure 1. In particular, the 241 root selects the Instance that will be used to forward the packet 242 within the RPL domain. 244 4.2. Outgoing Packets 246 When routing a packet outside the RPL domain, the root applies a 247 policy to determine whether the Flow Label was used to carry the RPL 248 information. If so, the root MUST reset the Flow Label. The root 249 SHOULD recompute a Flow Label following the rules prescribed by 250 [RFC6553]. In particular, the root MAY ignore the source address but 251 it SHOULD use the RPLInstanceID for the computation. 253 5. RPL node Operation 255 Depending on the policy in place, the source of a packet will decide 256 whether to use this specification to transport the RPL information in 257 the IPv6 packets. If it does, the source in the LLN SHOULD set the 258 Flow Label to zero and MUST NOT expect that the flow label will be 259 conserved end-to-end". 261 6. Security Considerations 263 The process of using the Flow Label as opposed to the RPL option does 264 not appear to create any opening for new threat compared to 265 [RFC6553]. 267 7. IANA Considerations 269 No IANA action is required for this specification. 271 8. Acknowledgments 273 The author wishes to thank Brian Carpenter for his in-depth review 274 and constructive approach to the problem and its resolution. 276 9. References 278 9.1. Normative References 280 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 281 Requirement Levels", BCP 14, RFC 2119, March 1997. 283 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 284 (IPv6) Specification", RFC 2460, December 1998. 286 [RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 287 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 288 September 2011. 290 [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., 291 Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. 292 Alexander, "RPL: IPv6 Routing Protocol for Low-Power and 293 Lossy Networks", RFC 6550, March 2012. 295 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 296 Power and Lossy Networks (RPL) Option for Carrying RPL 297 Information in Data-Plane Datagrams", RFC 6553, 298 March 2012. 300 9.2. Informative References 302 [I-D.ietf-roll-terminology] 303 Vasseur, J., "Terminology in Low power And Lossy 304 Networks", draft-ietf-roll-terminology-06 (work in 305 progress), September 2011. 307 [I-D.thubert-roll-forwarding-frags] 308 Thubert, P. and J. Hui, "LLN Fragment Forwarding and 309 Recovery", draft-thubert-roll-forwarding-frags-00 (work in 310 progress), March 2012. 312 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 313 "Transmission of IPv6 Packets over IEEE 802.15.4 314 Networks", RFC 4944, September 2007. 316 [RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney, 317 "Industrial Routing Requirements in Low-Power and Lossy 318 Networks", RFC 5673, October 2009. 320 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, 321 "IPv6 Flow Label Specification", RFC 6437, November 2011. 323 Author's Address 325 Pascal Thubert (editor) 326 Cisco Systems 327 Village d'Entreprises Green Side 328 400, Avenue de Roumanille 329 Batiment T3 330 Biot - Sophia Antipolis 06410 331 FRANCE 333 Phone: +33 4 97 23 26 34 334 Email: pthubert@cisco.com