idnits 2.17.1 draft-ietf-ipsecme-iptfs-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 1289 has weird spacing: '...4 any any...' == Line 1305 has weird spacing: '...4 any any...' -- The document date (March 30, 2021) is 1116 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: '--800--' is mentioned on line 1107, but not defined -- Looks like a reference, but probably isn't: '60' on line 1107 == Missing Reference: '-240-' is mentioned on line 1107, but not defined == Missing Reference: '--4000----------------------' is mentioned on line 1107, but not defined -- Obsolete informational reference (is this intentional?): RFC 8229 (Obsoleted by RFC 9329) Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Hopps 3 Internet-Draft LabN Consulting, L.L.C. 4 Intended status: Standards Track March 30, 2021 5 Expires: October 1, 2021 7 IP-TFS: Aggregation and Fragmentation Mode for ESP and its Use for IP 8 Traffic Flow Security 9 draft-ietf-ipsecme-iptfs-08 11 Abstract 13 This document describes a mechanism for aggregation and fragmentation 14 of IP packets when they are being encapsulated in ESP payload. This 15 new payload type can be used for various purposes such as decreasing 16 encapsulation overhead for small IP packets; however, the focus in 17 this document is to enhance IPsec traffic flow security (IP-TFS) by 18 adding Traffic Flow Confidentiality (TFC) to encrypted IP 19 encapsulated traffic. TFC is provided by obscuring the size and 20 frequency of IP traffic using a fixed-sized, constant-send-rate IPsec 21 tunnel. The solution allows for congestion control as well as non- 22 constant send-rate usage. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on October 1, 2021. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Terminology & Concepts . . . . . . . . . . . . . . . . . 4 60 2. The AGGFRAG Tunnel . . . . . . . . . . . . . . . . . . . . . 4 61 2.1. Tunnel Content . . . . . . . . . . . . . . . . . . . . . 4 62 2.2. Payload Content . . . . . . . . . . . . . . . . . . . . . 5 63 2.2.1. Data Blocks . . . . . . . . . . . . . . . . . . . . . 6 64 2.2.2. End Padding . . . . . . . . . . . . . . . . . . . . . 6 65 2.2.3. Fragmentation, Sequence Numbers and All-Pad Payloads 6 66 2.2.4. Empty Payload . . . . . . . . . . . . . . . . . . . . 8 67 2.2.5. IP Header Value Mapping . . . . . . . . . . . . . . . 8 68 2.2.6. IP Time-To-Live (TTL) and Tunnel errors . . . . . . . 9 69 2.2.7. Effective MTU of the Tunnel . . . . . . . . . . . . . 9 70 2.3. Exclusive SA Use . . . . . . . . . . . . . . . . . . . . 9 71 2.4. Modes of Operation . . . . . . . . . . . . . . . . . . . 10 72 2.4.1. Non-Congestion Controlled Mode . . . . . . . . . . . 10 73 2.4.2. Congestion Controlled Mode . . . . . . . . . . . . . 10 74 2.5. Summary of Receiver Processing . . . . . . . . . . . . . 12 75 3. Congestion Information . . . . . . . . . . . . . . . . . . . 12 76 3.1. ECN Support . . . . . . . . . . . . . . . . . . . . . . . 13 77 4. Configuration of AGGFRAG Tunnels for IP-TFS . . . . . . . . . 14 78 4.1. Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 14 79 4.2. Fixed Packet Size . . . . . . . . . . . . . . . . . . . . 14 80 4.3. Congestion Control . . . . . . . . . . . . . . . . . . . 14 81 5. IKEv2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 82 5.1. USE_AGGFRAG Notification Message . . . . . . . . . . . . 14 83 6. Packet and Data Formats . . . . . . . . . . . . . . . . . . . 15 84 6.1. AGGFRAG_PAYLOAD Payload . . . . . . . . . . . . . . . . . 15 85 6.1.1. Non-Congestion Control AGGFRAG_PAYLOAD Payload Format 16 86 6.1.2. Congestion Control AGGFRAG_PAYLOAD Payload Format . . 16 87 6.1.3. Data Blocks . . . . . . . . . . . . . . . . . . . . . 18 88 6.1.4. IKEv2 USE_AGGFRAG Notification Message . . . . . . . 20 89 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 90 7.1. AGGFRAG_PAYLOAD Sub-Type Registry . . . . . . . . . . . . 21 91 7.2. USE_AGGFRAG Notify Message Status Type . . . . . . . . . 21 92 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 93 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 94 9.1. Normative References . . . . . . . . . . . . . . . . . . 22 95 9.2. Informative References . . . . . . . . . . . . . . . . . 22 96 Appendix A. Example Of An Encapsulated IP Packet Flow . . . . . 24 97 Appendix B. A Send and Loss Event Rate Calculation . . . . . . . 25 98 Appendix C. Comparisons of IP-TFS . . . . . . . . . . . . . . . 25 99 C.1. Comparing Overhead . . . . . . . . . . . . . . . . . . . 25 100 C.1.1. IP-TFS Overhead . . . . . . . . . . . . . . . . . . . 26 101 C.1.2. ESP with Padding Overhead . . . . . . . . . . . . . . 26 102 C.2. Overhead Comparison . . . . . . . . . . . . . . . . . . . 27 103 C.3. Comparing Available Bandwidth . . . . . . . . . . . . . . 28 104 C.3.1. Ethernet . . . . . . . . . . . . . . . . . . . . . . 28 105 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 30 106 Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 30 107 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 30 109 1. Introduction 111 Traffic Analysis ([RFC4301], [AppCrypt]) is the act of extracting 112 information about data being sent through a network. While directly 113 obscuring the data with encryption [RFC4303], the traffic pattern 114 itself exposes information due to variations in its shape and timing 115 ([RFC8546], [AppCrypt]). Hiding the size and frequency of traffic is 116 referred to as Traffic Flow Confidentiality (TFC) per [RFC4303]. 118 [RFC4303] provides for TFC by allowing padding to be added to 119 encrypted IP packets and allowing for transmission of all-pad packets 120 (indicated using protocol 59). This method has the major limitation 121 that it can significantly under-utilize the available bandwidth. 123 This document defines an aggregation and fragmentation (AGGFRAG) mode 124 for ESP, and its use for IP Traffic Flow Security (IP-TFS). This 125 solution provides for full TFC without the aforementioned bandwidth 126 limitation. This is accomplished by using a constant-send-rate IPsec 127 [RFC4303] tunnel with fixed-sized encapsulating packets; however, 128 these fixed-sized packets can contain partial, whole or multiple IP 129 packets to maximize the bandwidth of the tunnel. A non-constant 130 send-rate is allowed, but the confidentiality properties of its use 131 are outside the scope of this document. 133 For a comparison of the overhead of IP-TFS with the RFC4303 134 prescribed TFC solution see Appendix C. 136 Additionally, IP-TFS provides for operating fairly within congested 137 networks [RFC2914]. This is important for when the IP-TFS user is 138 not in full control of the domain through which the IP-TFS tunnel 139 path flows. 141 The mechanisms, such as the AGGFRAG mode, defined in this document 142 are generic with the intent of allowing for non-TFS uses, but such 143 uses are outside the scope of this document. 145 1.1. Terminology & Concepts 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 149 "OPTIONAL" in this document are to be interpreted as described in BCP 150 14 [RFC2119] [RFC8174] when, and only when, they appear in all 151 capitals, as shown here. 153 This document assumes familiarity with IP security concepts including 154 TFC as described in [RFC4301]. 156 2. The AGGFRAG Tunnel 158 As mentioned in Section 1, AGGFRAG mode utilizes an IPsec [RFC4303] 159 tunnel as its transport. For the purpose of IP-TFS, fixed-sized 160 encapsulating packets are sent at a constant rate on the AGGFRAG 161 tunnel. 163 The primary input to the tunnel algorithm is the requested bandwidth 164 to be used by the tunnel. Two values are then required to provide 165 for this bandwidth use, the fixed size of the encapsulating packets, 166 and rate at which to send them. 168 The fixed packet size MAY either be specified manually or be 169 determined through other methods such as the Packetization Layer MTU 170 Discovery (PLMTUD) ([RFC4821], [RFC8899]) or Path MTU discovery 171 (PMTUD) ([RFC1191], [RFC8201]). PMTUD is known to have issues so 172 PLMTUD is considered the more robust option. For PLMTUD, congestion 173 control payloads can be used as in-band probes (see Section 6.1.2 and 174 [RFC8899]). 176 Given the encapsulating packet size and the requested bandwidth to be 177 used, the corresponding packet send rate can be calculated. The 178 packet send rate is the requested bandwidth to be used divided by the 179 size of the encapsulating packet. 181 The egress (receiving) side of the AGGFRAG tunnel MUST allow for and 182 expect the ingress (sending) side of the AGGFRAG tunnel to vary the 183 size and rate of sent encapsulating packets, unless constrained by 184 other policy. 186 2.1. Tunnel Content 188 As previously mentioned, one issue with the TFC padding solution in 189 [RFC4303] is the large amount of wasted bandwidth as only one IP 190 packet can be sent per encapsulating packet. In order to maximize 191 bandwidth, IP-TFS breaks this one-to-one association by introducing 192 an AGGFRAG mode for ESP. 194 AGGFRAG mode aggregates as well as fragments the inner IP traffic 195 flow into encapsulating IPsec tunnel packets. For IP-TFS, the IPsec 196 encapsulating tunnel packets are a fixed size. Padding is only added 197 to the the tunnel packets if there is no data available to be sent at 198 the time of tunnel packet transmission, or if fragmentation has been 199 disabled by the receiver. 201 This is accomplished using a new Encapsulating Security Payload (ESP, 202 [RFC4303]) Next Header field value AGGFRAG_PAYLOAD (Section 6.1). 204 Other non-IP-TFS uses of this AGGFRAG mode have been suggested, such 205 as increased performance through packet aggregation, as well as 206 handling MTU issues using fragmentation. These uses are not defined 207 here, but are also not restricted by this document. 209 2.2. Payload Content 211 The AGGFRAG_PAYLOAD payload content defined in this document is 212 comprised of a 4 or 24 octet header followed by either a partial 213 datablock, a full datablock, or multiple partial or full datablocks. 214 The following diagram illustrates this payload within the ESP packet. 215 See Section 6.1 for the exact formats of the AGGFRAG_PAYLOAD payload. 217 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 . Outer Encapsulating Header ... . 219 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 . ESP Header... . 221 +---------------------------------------------------------------+ 222 | [AGGFRAG subtype/flags] : BlockOffset | 223 +---------------------------------------------------------------+ 224 : [Optional Congestion Info] : 225 +---------------------------------------------------------------+ 226 | DataBlocks ... ~ 227 ~ ~ 228 ~ | 229 +---------------------------------------------------------------| 230 . ESP Trailer... . 231 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Figure 1: Layout of an AGGFRAG mode IPsec Packet 235 The "BlockOffset" value is either zero or some offset into or past 236 the end of the "DataBlocks" data. 238 If the "BlockOffset" value is zero it means that the "DataBlocks" 239 data begins with a new data block. 241 Conversely, if the "BlockOffset" value is non-zero it points to the 242 start of the new data block, and the initial "DataBlocks" data 243 belongs to the data block that is still being re-assembled. 245 If the "BlockOffset" points past the end of the "DataBlocks" data 246 then the next data block occurs in a subsequent encapsulating packet. 248 Having the "BlockOffset" always point at the next available data 249 block allows for recovering the next inner packet in the presence of 250 outer encapsulating packet loss. 252 An example AGGFRAG mode packet flow can be found in Appendix A. 254 2.2.1. Data Blocks 256 +---------------------------------------------------------------+ 257 | Type | rest of IPv4, IPv6 or pad. 258 +-------- 260 Figure 2: Layout of a DataBlock 262 A data block is defined by a 4-bit type code followed by the data 263 block data. The type values have been carefully chosen to coincide 264 with the IPv4/IPv6 version field values so that no per-data block 265 type overhead is required to encapsulate an IP packet. Likewise, the 266 length of the data block is extracted from the encapsulated IPv4's 267 "Total Length" or IPv6's "Payload Length" fields. 269 2.2.2. End Padding 271 Since a data block's type is identified in its first 4-bits, the only 272 time padding is required is when there is no data to encapsulate. 273 For this end padding a "Pad Data Block" is used. 275 2.2.3. Fragmentation, Sequence Numbers and All-Pad Payloads 277 In order for a receiver to reassemble fragmented inner-packets, the 278 sender MUST send the inner-packet fragments back-to-back in the 279 logical outer packet stream (i.e., using consecutive ESP sequence 280 numbers). However, the sender is allowed to insert "all-pad" 281 payloads (i.e., payloads with a "BlockOffset" of zero and a single 282 pad "DataBlock") in between the packets carrying the inner-packet 283 fragment payloads. This interleaving of all-pad payloads allows the 284 sender to always send a tunnel packet, regardless of the 285 encapsulation computational requirements. 287 When a receiver is reassembling an inner-packet, and it receives an 288 "all-pad" payload, it increments the expected sequence number that 289 the next inner-packet fragment is expected to arrive in. 291 Given the above, the receiver will need to handle out-of-order 292 arrival of outer ESP packets prior to reassembly processing. ESP 293 already provides for optionally detecting replay attacks. Detecting 294 replay attacks normally utilizes a window method. A similar sequence 295 number based sliding window can be used to correct re-ordering of the 296 outer packet stream. Receiving a larger (newer) sequence number 297 packet advances the window, and received older ESP packets whose 298 sequence numbers the window has passed by are dropped. A good choice 299 for the size of this window depends on the amount of re-ordering the 300 user may normally experience. 302 As the amount of reordering that may be present is hard to predict, 303 the window size SHOULD be configurable by the user. Implementations 304 MAY also dynamically adjust the reordering window based on actual 305 reordering seen in arriving packets. Finally, note that as IP-TFS is 306 sending a continuous stream of packets there is no requirement for 307 timers (although there's no prohibition either) as newly arrived 308 packets will cause the window to advance and older packets will then 309 be processed as they leave the window. Implementations that are 310 concerned about memory use when packets are delayed (e.g., when an SA 311 deletion is delayed), or non-IP-TFS uses of AGGFRAG mode, can of 312 course use timers to drop packets as well. 314 While ESP guarantees an increasing sequence number with subsequently 315 sent packets, it does not actually require the sequence numbers to be 316 generated with no gaps (e.g., sending only even numbered sequence 317 numbers would be allowed as long as they are always increasing). 318 Gaps in the sequence numbers will not work for this document so the 319 sequence number stream MUST increase monotonically by 1 for each 320 subsequent packet. 322 When using the AGGFRAG_PAYLOAD in conjunction with replay detection, 323 the window size for both can be reduced to the smaller of the two 324 window sizes. This is because packets outside of the smaller window 325 but inside the larger would still be dropped by the mechanism with 326 the smaller window size. 328 Finally, as sequence numbers are reset when switching SAs (e.g., when 329 re-keying a child SA), senders MUST NOT send initial fragments of an 330 inner packet using one SA and subsequent fragments in a different SA. 332 2.2.3.1. Optional Extra Padding 334 When the tunnel bandwidth is not being fully utilized, a sender MAY 335 pad-out the current encapsulating packet in order to deliver an inner 336 packet un-fragmented in the following outer packet. The benefit 337 would be to avoid inner-packet fragmentation in the presence of a 338 bursty offered load (non-bursty traffic will naturally not fragment). 339 Senders MAY also choose to allow for a minimum fragment size to be 340 configured (e.g., as a percentage of the AGGFRAG_PAYLOAD payload 341 size) to avoid fragmentation at the cost of tunnel bandwidth. The 342 cost with these methods is complexity and added delay of inner 343 traffic. The main advantage to avoiding fragmentation is to minimize 344 inner packet loss in the presence of outer packet loss. When this is 345 worthwhile (e.g., how much loss and what type of loss is required, 346 given different inner traffic shapes and utilization, for this to 347 make sense), and what values to use for the allowable/added delay may 348 be worth researching, but is outside the scope of this document. 350 While use of padding to avoid fragmentation does not impact 351 interoperability, used inappropriately it can reduce the effective 352 throughput of a tunnel. Senders implementing either of the above 353 approaches will need to take care to not reduce the effective 354 capacity, and overall utility, of the tunnel through the overuse of 355 padding. 357 2.2.4. Empty Payload 359 To support reporting of congestion control information (described 360 later) using a non-AGGFRAG_PAYLOAD enabled SA, it is allowed to send 361 an AGGFRAG_PAYLOAD payload with no data blocks (i.e., the ESP payload 362 length is equal to the AGGFRAG_PAYLOAD header length). This special 363 payload is called an empty payload. 365 Currently this situation is only applicable in non-IKEv2 use cases. 367 2.2.5. IP Header Value Mapping 369 [RFC4301] provides some direction on when and how to map various 370 values from an inner IP header to the outer encapsulating header, 371 namely the Don't-Fragment (DF) bit ([RFC0791] and [RFC8200]), the 372 Differentiated Services (DS) field [RFC2474] and the Explicit 373 Congestion Notification (ECN) field [RFC3168]. Unlike [RFC4301], 374 AGGFRAG mode may and often will be encapsulating more than one IP 375 packet per ESP packet. To deal with this, these mappings are 376 restricted further. 378 2.2.5.1. DF bit 380 AGGFRAG mode never maps the inner DF bit as it is unrelated to the 381 AGGFRAG tunnel functionality; AGGFRAG mode never needs to IP fragment 382 the inner packets and the inner packets will not affect the 383 fragmentation of the outer encapsulation packets. 385 2.2.5.2. ECN value 387 The ECN value need not be mapped as any congestion related to the 388 constant-send-rate IP-TFS tunnel is unrelated (by design) to the 389 inner traffic flow. The sender MAY still set the ECN value of inner 390 packets based on the normal ECN specification [RFC3168]. 392 2.2.5.3. DS field 394 By default the DS field SHOULD NOT be copied, although a sender MAY 395 choose to allow for configuration to override this behavior. A 396 sender SHOULD also allow the DS value to be set by configuration. 398 2.2.6. IP Time-To-Live (TTL) and Tunnel errors 400 [RFC4301] specifies how to modify the inner packet TTL [RFC0791]. 402 Any errors (e.g., ICMP errors arriving back at the tunnel ingress due 403 to tunnel traffic) are handled the same as with non-AGGFRAG IPsec 404 tunnels. 406 2.2.7. Effective MTU of the Tunnel 408 Unlike [RFC4301], there is normally no effective MTU (EMTU) on an 409 AGGFRAG tunnel as all IP packet sizes are properly transmitted 410 without requiring IP fragmentation prior to tunnel ingress. That 411 said, a sender MAY allow for explicitly configuring an MTU for the 412 tunnel. 414 If fragmentation has been disabled on the AGGFRAG tunnel, then the 415 tunnel's EMTU and behaviors are the same as normal IPsec tunnels 416 [RFC4301]. 418 2.3. Exclusive SA Use 420 This document does not specify mixed use of an AGGFRAG_PAYLOAD 421 enabled SA. A sender MUST only send AGGFRAG_PAYLOAD payloads over an 422 SA configured for AGGFRAG mode. 424 2.4. Modes of Operation 426 Just as with normal IPsec/ESP tunnels, AGGFRAG tunnels are 427 unidirectional. Bidirectional IP-TFS functionality is achieved by 428 setting up 2 AGGFRAG tunnels, one in either direction. 430 An AGGFRAG tunnel used for IP-TFS can operate in 2 modes, a non- 431 congestion controlled mode and congestion controlled mode. 433 2.4.1. Non-Congestion Controlled Mode 435 In the non-congestion controlled mode, IP-TFS sends fixed-sized 436 packets over an AGGFRAG tunnel at a constant rate. The packet send 437 rate is constant and is not automatically adjusted regardless of any 438 network congestion (e.g., packet loss). 440 For similar reasons as given in [RFC7510] the non-congestion 441 controlled mode should only be used where the user has full 442 administrative control over the path the tunnel will take. This is 443 required so the user can guarantee the bandwidth and also be sure as 444 to not be negatively affecting network congestion [RFC2914]. In this 445 case packet loss should be reported to the administrator (e.g., via 446 syslog, YANG notification, SNMP traps, etc) so that any failures due 447 to a lack of bandwidth can be corrected. 449 Non-congestion control mode is also appropriate if ESP over TCP is in 450 use [RFC8229]. 452 2.4.2. Congestion Controlled Mode 454 With the congestion controlled mode, IP-TFS adapts to network 455 congestion by lowering the packet send rate to accommodate the 456 congestion, as well as raising the rate when congestion subsides. 457 Since overhead is per packet, by allowing for maximal fixed-size 458 packets and varying the send rate transport overhead is minimized. 460 The output of the congestion control algorithm will adjust the rate 461 at which the ingress sends packets. While this document does not 462 require a specific congestion control algorithm, best current 463 practice RECOMMENDS that the algorithm conform to [RFC5348]. 464 Congestion control principles are documented in [RFC2914] as well. 465 [RFC4342] provides an example of the [RFC5348] algorithm which 466 matches the requirements of IP-TFS (i.e., designed for fixed-size 467 packet and send rate varied based on congestion. 469 The required inputs for the TCP friendly rate control algorithm 470 described in [RFC5348] are the receiver's loss event rate and the 471 sender's estimated round-trip time (RTT). These values are provided 472 by IP-TFS using the congestion information header fields described in 473 Section 3. In particular, these values are sufficient to implement 474 the algorithm described in [RFC5348]. 476 At a minimum, the congestion information MUST be sent, from the 477 receiver and from the sender, at least once per RTT. Prior to 478 establishing an RTT the information SHOULD be sent constantly from 479 the sender and the receiver so that an RTT estimate can be 480 established. Not receiving this information over multiple 481 consecutive RTT intervals should be considered a congestion event 482 that causes the sender to adjust its sending rate lower. For 483 example, [RFC4342] calls this the "no feedback timeout" and it is 484 equal to 4 RTT intervals. When a "no feedback timeout" has occurred 485 [RFC4342] halves the sending rate. 487 An implementation MAY choose to always include the congestion 488 information in its AGGFRAG payload header if sending on an IP-TFS 489 enabled SA. Since IP-TFS normally will operate with a large packet 490 size, the congestion information should represent a small portion of 491 the available tunnel bandwidth. An implementation choosing to always 492 send the data MAY also choose to only update the "LossEventRate" and 493 "RTT" header field values it sends every "RTT" though. 495 When choosing a congestion control algorithm (or a selection of 496 algorithms) note that IP-TFS is not providing for reliable delivery 497 of IP traffic, and so per packet ACKs are not required and are not 498 provided. 500 It is worth noting that the variable send-rate of a congestion 501 controlled AGGFRAG tunnel, is not private; however, this send-rate is 502 being driven by network congestion, and as long as the encapsulated 503 (inner) traffic flow shape and timing are not directly affecting the 504 (outer) network congestion, the variations in the tunnel rate will 505 not weaken the provided inner traffic flow confidentiality. 507 2.4.2.1. Circuit Breakers 509 In additional to congestion control, implementations MAY choose to 510 define and implement circuit breakers [RFC8084] as a recovery method 511 of last resort. Enabling circuit breakers is also a reason a user 512 may wish to enable congestion information reports even when using the 513 non-congestion controlled mode of operation. The definition of 514 circuit breakers are outside the scope of this document. 516 2.5. Summary of Receiver Processing 518 An AGGFRAG enabled SA receiver has a few tasks to perform. 520 The receiver first reorders, possibly out-of-order ESP packets 521 received on an SA into in-sequence-order AGGFRAG_PAYLOAD payloads 522 (Section 2.2.3). If congestion control is enabled, the receiver 523 considers a packet lost when it's sequence number is abandoned (e.g., 524 pushed out of the re-ordering window, or timed-out) by the reordering 525 algorithm. 527 Additionally, if congestion control is enabled, the receiver sends 528 congestion control data (Section 6.1.2) back to the sender as 529 described in Section 2.4.2 and Section 3. 531 Finally, the receiver processes the now in-order AGGFRAG_PAYLOAD 532 payload stream to extract the inner-packets (Section 2.2.3, 533 Section 6.1). 535 3. Congestion Information 537 In order to support the congestion control mode, the sender needs to 538 know the loss event rate and to approximate the RTT [RFC5348]. In 539 order to obtain these values, the receiver sends congestion control 540 information on it's SA back to the sender. Thus, to support 541 congestion control the receiver must have a paired SA back to the 542 sender (this is always the case when the tunnel was created using 543 IKEv2). If the SA back to the sender is a non-AGGFRAG_PAYLOAD 544 enabled SA then an AGGFRAG_PAYLOAD empty payload (i.e., header only) 545 is used to convey the information. 547 In order to calculate a loss event rate compatible with [RFC5348], 548 the receiver needs to have a round-trip time estimate. Thus the 549 sender communicates this estimate in the "RTT" header field. On 550 startup this value will be zero as no RTT estimate is yet known. 552 In order for the sender to estimate its "RTT" value, the sender 553 places a timestamp value in the "TVal" header field. On first 554 receipt of this "TVal", the receiver records the new "TVal" value 555 along with the time it arrived locally, subsequent receipt of the 556 same "TVal" MUST NOT update the recorded time. 558 When the receiver sends its CC header it places this latest recorded 559 "TVal" in the "TEcho" header field, along with 2 delay values, "Echo 560 Delay" and "Transmit Delay". The "Echo Delay" value is the time 561 delta from the recorded arrival time of "TVal" and the current clock 562 in microseconds. The second value, "Transmit Delay", is the 563 receiver's current transmission delay on the tunnel (i.e., the 564 average time between sending packets on its half of the AGGFRAG 565 tunnel). 567 When the sender receives back its "TVal" in the "TEcho" header field 568 it calculates 2 RTT estimates. The first is the actual delay found 569 by subtracting the "TEcho" value from its current clock and then 570 subtracting "Echo Delay" as well. The second RTT estimate is found 571 by adding the received "Transmit Delay" header value to the senders 572 own transmission delay (i.e., the average time between sending 573 packets on its half of the AGGFRAG tunnel). The larger of these 2 574 RTT estimates SHOULD be used as the "RTT" value. 576 The two RTT estimates are required to handle different combinations 577 of faster or slower tunnel packet paths with faster or slower fixed 578 tunnel rates. Choosing the larger of the two values guarantees that 579 the "RTT" is never considered faster than the aggregate transmission 580 delay based on the IP-TFS send rate (the second estimate), as well as 581 never being considered faster than the actual RTT along the tunnel 582 packet path (the first estimate). 584 The receiver also calculates, and communicates in the "LossEventRate" 585 header field, the loss event rate for use by the sender. This is 586 slightly different from [RFC4342] which periodically sends all the 587 loss interval data back to the sender so that it can do the 588 calculation. See Appendix B for a suggested way to calculate the 589 loss event rate value. Initially this value will be zero (indicating 590 no loss) until enough data has been collected by the receiver to 591 update it. 593 3.1. ECN Support 595 In additional to normal packet loss information AGGFRAG mode supports 596 use of the ECN bits in the encapsulating IP header [RFC3168] for 597 identifying congestion. If ECN use is enabled and a packet arrives 598 at the egress (receiving) side with the Congestion Experienced (CE) 599 value set, then the receiver considers that packet as being dropped, 600 although it does not drop it. The receiver MUST set the E bit in any 601 AGGFRAG_PAYLOAD payload header containing a "LossEventRate" value 602 derived from a CE value being considered. 604 As noted in [RFC3168] the ECN bits are not protected by IPsec and 605 thus may constitute a covert channel. For this reason, ECN use 606 SHOULD NOT be enabled by default. 608 4. Configuration of AGGFRAG Tunnels for IP-TFS 610 IP-TFS is meant to be deployable with a minimal amount of 611 configuration. All IP-TFS specific configuration should be specified 612 at the unidirectional tunnel ingress (sending) side. It is intended 613 that non-IKEv2 operation is supported, at least, with local static 614 configuration. 616 4.1. Bandwidth 618 Bandwidth is a local configuration option. For non-congestion 619 controlled mode, the bandwidth SHOULD be configured. For congestion 620 controlled mode, the bandwidth can be configured or the congestion 621 control algorithm discovers and uses the maximum bandwidth available. 622 No standardized configuration method is required. 624 4.2. Fixed Packet Size 626 The fixed packet size to be used for the tunnel encapsulation packets 627 MAY be configured manually or can be automatically determined using 628 other methods such as PLMTUD ([RFC4821], [RFC8899]) or PMTUD 629 ([RFC1191], [RFC8201]). As PMTUD is known to have issues, PLMTUD is 630 considered the more robust option. No standardized configuration 631 method is required. 633 4.3. Congestion Control 635 Congestion control is a local configuration option. No standardized 636 configuration method is required. 638 5. IKEv2 640 5.1. USE_AGGFRAG Notification Message 642 As mentioned previously AGGFRAG tunnels utilize ESP payloads of type 643 AGGFRAG_PAYLOAD. 645 When using IKEv2, a new "USE_AGGFRAG" Notification Message enables 646 the AGGFRAG_PAYLOAD payload on a child SA pair. The method used is 647 similar to how USE_TRANSPORT_MODE is negotiated, as described in 648 [RFC7296]. 650 To request use of the AGGFRAG_PAYLOAD payload on the Child SA pair, 651 the initiator includes the USE_AGGFRAG notification in an SA payload 652 requesting a new Child SA (either during the initial IKE_AUTH or 653 during CREATE_CHILD_SA exchanges). If the request is accepted then 654 the response MUST also include a notification of type USE_AGGFRAG. 655 If the responder declines the request the child SA will be 656 established without AGGFRAG_PAYLOAD payload use enabled. If this is 657 unacceptable to the initiator, the initiator MUST delete the child 658 SA. 660 As the use of the AGGFRAG_PAYLOAD payload is currently only defined 661 for non-transport mode tunnels, the USE_AGGFRAG notification MUST NOT 662 be combined with USE_TRANSPORT notification. 664 The USE_AGGFRAG notification contains a 1 octet payload of flags that 665 specify requirements from the sender of the notification. If any 666 requirement flags are not understood or cannot be supported by the 667 receiver then the receiver SHOULD NOT enable use of AGGFRAG_PAYLOAD 668 (either by not responding with the USE_AGGFRAG notification, or in 669 the case of the initiator, by deleting the child SA if the now 670 established non-AGGFRAG_PAYLOAD using SA is unacceptable). 672 The notification type and payload flag values are defined in 673 Section 6.1.4. 675 6. Packet and Data Formats 677 The packet and data formats defined below are generic with the intent 678 of allowing for non-IP-TFS uses, but such uses are outside the scope 679 of this document. 681 6.1. AGGFRAG_PAYLOAD Payload 683 ESP Next Header value: 0x5 685 An AGGFRAG payload is identified by the ESP Next Header value 686 AGGFRAG_PAYLOAD which has the value 0x5. The value 5 was chosen to 687 not conflict with other used values. The first octet of this payload 688 indicates the format of the remaining payload data. 690 0 1 2 3 4 5 6 7 691 +-+-+-+-+-+-+-+-+-+-+- 692 | Sub-type | ... 693 +-+-+-+-+-+-+-+-+-+-+- 695 Sub-type: 696 An 8-bit value indicating the payload format. 698 This document defines 2 payload sub-types. These payload formats are 699 defined in the following sections. 701 6.1.1. Non-Congestion Control AGGFRAG_PAYLOAD Payload Format 703 The non-congestion control AGGFRAG_PAYLOAD payload is comprised of a 704 4 octet header followed by a variable amount of "DataBlocks" data as 705 shown below. 707 1 2 3 708 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 1 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 | Sub-Type (0) | Reserved | BlockOffset | 711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 712 | DataBlocks ... 713 +-+-+-+-+-+-+-+-+-+-+- 715 Sub-type: 716 An octet indicating the payload format. For this non-congestion 717 control format, the value is 0. 719 Reserved: 720 An octet set to 0 on generation, and ignored on receipt. 722 BlockOffset: 723 A 16-bit unsigned integer counting the number of octets of 724 "DataBlocks" data before the start of a new data block. If the 725 start of a new data block occurs in a subsequent payload the 726 "BlockOffset" will point past the end of the "DataBlocks" data. 727 In this case all the "DataBlocks" data belongs to the current data 728 block being assembled. When the "BlockOffset" extends into 729 subsequent payloads it continues to only count "DataBlocks" data 730 (i.e., it does not count subsequent packets non-"DataBlocks" data 731 such as header octets). 733 DataBlocks: 734 Variable number of octets that begins with the start of a data 735 block, or the continuation of a previous data block, followed by 736 zero or more additional data blocks. 738 6.1.2. Congestion Control AGGFRAG_PAYLOAD Payload Format 740 The congestion control AGGFRAG_PAYLOAD payload is comprised of a 24 741 octet header followed by a variable amount of "DataBlocks" data as 742 shown below. 744 1 2 3 745 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 1 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 747 | Sub-type (1) | Reserved |P|E| BlockOffset | 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | LossEventRate | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 751 | RTT | Echo Delay ... 752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 753 ... Echo Delay | Transmit Delay | 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 755 | TVal | 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 | TEcho | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | DataBlocks ... 760 +-+-+-+-+-+-+-+-+-+-+- 762 Sub-type: 763 An octet indicating the payload format. For this congestion 764 control format, the value is 1. 766 Reserved: 767 A 6-bit field set to 0 on generation, and ignored on receipt. 769 P: 770 A 1-bit value if set indicates that PLMTUD probing is in progress. 771 This information can be used to avoid treating missing packets as 772 loss events by the CC algorithm when running the PLMTUD probe 773 algorithm. 775 E: 776 A 1-bit value if set indicates that Congestion Experienced (CE) 777 ECN bits were received and used in deriving the reported 778 "LossEventRate". 780 BlockOffset: 781 The same value as the non-congestion controlled payload format 782 value. 784 LossEventRate: 785 A 32-bit value specifying the inverse of the current loss event 786 rate as calculated by the receiver. A value of zero indicates no 787 loss. Otherwise the loss event rate is "1/LossEventRate". 789 RTT: 790 A 22-bit value specifying the sender's current round-trip time 791 estimate in microseconds. The value MAY be zero prior to the 792 sender having calculated a round-trip time estimate. The value 793 SHOULD be set to zero on non-AGGFRAG_PAYLOAD enabled SAs. If the 794 value is equal to or larger than "0x3FFFFF" it MUST be set to 795 "0x3FFFFF". 797 Echo Delay: 798 A 21-bit value specifying the delay in microseconds incurred 799 between the receiver first receiving the "TVal" value which it is 800 sending back in "TEcho". If the value is equal to or larger than 801 "0x1FFFFF" it MUST be set to "0x1FFFFF". 803 Transmit Delay: 804 A 21-bit value specifying the transmission delay in microseconds. 805 This is the fixed (or average) delay on the receiver between it 806 sending packets on the IPTFS tunnel. If the value is equal to or 807 larger than "0x1FFFFF" it MUST be set to "0x1FFFFF". 809 TVal: 810 An opaque 32-bit value that will be echoed back by the receiver in 811 later packets in the "TEcho" field, along with an "Echo Delay" 812 value of how long that echo took. 814 TEcho: 815 The opaque 32-bit value from a received packet's "TVal" field. 816 The received "TVal" is placed in "TEcho" along with an "Echo 817 Delay" value indicating how long it has been since receiving the 818 "TVal" value. 820 DataBlocks: 821 Variable number of octets that begins with the start of a data 822 block, or the continuation of a previous data block, followed by 823 zero or more additional data blocks. For the special case of 824 sending congestion control information on an non-IP-TFS enabled SA 825 this value MUST be empty (i.e., be zero octets long). 827 6.1.3. Data Blocks 829 1 2 3 830 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 1 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 832 | Type | IPv4, IPv6 or pad... 833 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 835 Type: 836 A 4-bit field where 0x0 identifies a pad data block, 0x4 indicates 837 an IPv4 data block, and 0x6 indicates an IPv6 data block. 839 6.1.3.1. IPv4 Data Block 841 1 2 3 842 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 1 843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 844 | 0x4 | IHL | TypeOfService | TotalLength | 845 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 846 | Rest of the inner packet ... 847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 849 These values are the actual values within the encapsulated IPv4 850 header. In other words, the start of this data block is the start of 851 the encapsulated IP packet. 853 Type: 854 A 4-bit value of 0x4 indicating IPv4 (i.e., first nibble of the 855 IPv4 packet). 857 TotalLength: 858 The 16-bit unsigned integer "Total Length" field of the IPv4 inner 859 packet. 861 6.1.3.2. IPv6 Data Block 863 1 2 3 864 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 1 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | 0x6 | TrafficClass | FlowLabel | 867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 | PayloadLength | Rest of the inner packet ... 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 871 These values are the actual values within the encapsulated IPv6 872 header. In other words, the start of this data block is the start of 873 the encapsulated IP packet. 875 Type: 876 A 4-bit value of 0x6 indicating IPv6 (i.e., first nibble of the 877 IPv6 packet). 879 PayloadLength: 880 The 16-bit unsigned integer "Payload Length" field of the inner 881 IPv6 inner packet. 883 6.1.3.3. Pad Data Block 885 1 2 3 886 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 1 887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 888 | 0x0 | Padding ... 889 +-+-+-+-+-+-+-+-+-+-+- 891 Type: 892 A 4-bit value of 0x0 indicating a padding data block. 894 Padding: 895 Extends to end of the encapsulating packet. 897 6.1.4. IKEv2 USE_AGGFRAG Notification Message 899 As discussed in Section 5.1, a notification message USE_AGGFRAG is 900 used to negotiate use of the ESP AGGFRAG_PAYLOAD Next Header value. 902 The USE_AGGFRAG Notification Message State Type is (TBD2). 904 The notification payload contains 1 octet of requirement flags. 905 There are currently 2 requirement flags defined. This may be revised 906 by later specifications. 908 +-+-+-+-+-+-+-+-+ 909 |0|0|0|0|0|0|C|D| 910 +-+-+-+-+-+-+-+-+ 912 0: 913 6 bits - reserved, MUST be zero on send, unless defined by later 914 specifications. 916 C: 917 Congestion Control bit. If set, then the sender is requiring that 918 congestion control information MUST be returned to it periodically 919 as defined in Section 3. 921 D: 922 Don't Fragment bit. If set, indicates the sender of the notify 923 message does not support receiving packet fragments (i.e., inner 924 packets MUST be sent using a single "Data Block"). This value 925 only applies to what the sender is capable of receiving; the 926 sender MAY still send packet fragments unless similarly restricted 927 by the receiver in it's USE_AGGFRAG notification. 929 7. IANA Considerations 931 7.1. AGGFRAG_PAYLOAD Sub-Type Registry 933 This document requests IANA create a registry called "AGGFRAG_PAYLOAD 934 Sub-Type Registry" under a new category named "ESP AGGFRAG_PAYLOAD 935 Parameters". The registration policy for this registry is "Expert 936 Review" ([RFC8126] and [RFC7120]). 938 Name: 939 AGGFRAG_PAYLOAD Sub-Type Registry 941 Description: 942 AGGFRAG_PAYLOAD Payload Formats. 944 Reference: 945 This document 947 This initial content for this registry is as follows: 949 Sub-Type Name Reference 950 -------------------------------------------------------- 951 0 Non-Congestion Control Format This document 952 1 Congestion Control Format This document 953 3-255 Reserved 955 7.2. USE_AGGFRAG Notify Message Status Type 957 This document requests a status type USE_AGGFRAG be allocated from 958 the "IKEv2 Notify Message Types - Status Types" registry. 960 Value: 961 TBD2 963 Name: 964 USE_AGGFRAG 966 Reference: 967 This document 969 8. Security Considerations 971 This document describes an aggregation and fragmentation mechanism 972 and it use to add TFC to IP traffic. The use described is expected 973 to increase the security of the traffic being transported. Other 974 than the additional security afforded by using this mechanism, IP-TFS 975 utilizes the security protocols [RFC4303] and [RFC7296] and so their 976 security considerations apply to IP-TFS as well. 978 As noted in (Section 3.1) the ECN bits are not protected by IPsec and 979 thus may constitute a covert channel. For this reason, ECN use 980 SHOULD NOT be enabled by default. 982 As noted previously in Section 2.4.2, for TFC to be fully maintained 983 the encapsulated traffic flow should not be affecting network 984 congestion in a predictable way, and if it would be then non- 985 congestion controlled mode use should be considered instead. 987 9. References 989 9.1. Normative References 991 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 992 Requirement Levels", BCP 14, RFC 2119, 993 DOI 10.17487/RFC2119, March 1997, 994 . 996 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 997 RFC 4303, DOI 10.17487/RFC4303, December 2005, 998 . 1000 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 1001 Kivinen, "Internet Key Exchange Protocol Version 2 1002 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 1003 2014, . 1005 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1006 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1007 May 2017, . 1009 9.2. Informative References 1011 [AppCrypt] 1012 Schneier, B., "Applied Cryptography: Protocols, 1013 Algorithms, and Source Code in C", 11 2017. 1015 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1016 DOI 10.17487/RFC0791, September 1981, 1017 . 1019 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 1020 DOI 10.17487/RFC1191, November 1990, 1021 . 1023 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1024 "Definition of the Differentiated Services Field (DS 1025 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1026 DOI 10.17487/RFC2474, December 1998, 1027 . 1029 [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, 1030 RFC 2914, DOI 10.17487/RFC2914, September 2000, 1031 . 1033 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 1034 of Explicit Congestion Notification (ECN) to IP", 1035 RFC 3168, DOI 10.17487/RFC3168, September 2001, 1036 . 1038 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1039 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 1040 December 2005, . 1042 [RFC4342] Floyd, S., Kohler, E., and J. Padhye, "Profile for 1043 Datagram Congestion Control Protocol (DCCP) Congestion 1044 Control ID 3: TCP-Friendly Rate Control (TFRC)", RFC 4342, 1045 DOI 10.17487/RFC4342, March 2006, 1046 . 1048 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1049 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 1050 . 1052 [RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP 1053 Friendly Rate Control (TFRC): Protocol Specification", 1054 RFC 5348, DOI 10.17487/RFC5348, September 2008, 1055 . 1057 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 1058 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 1059 2014, . 1061 [RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black, 1062 "Encapsulating MPLS in UDP", RFC 7510, 1063 DOI 10.17487/RFC7510, April 2015, 1064 . 1066 [RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", 1067 BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017, 1068 . 1070 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1071 Writing an IANA Considerations Section in RFCs", BCP 26, 1072 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1073 . 1075 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1076 (IPv6) Specification", STD 86, RFC 8200, 1077 DOI 10.17487/RFC8200, July 2017, 1078 . 1080 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1081 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1082 DOI 10.17487/RFC8201, July 2017, 1083 . 1085 [RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation 1086 of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229, 1087 August 2017, . 1089 [RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a 1090 Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April 1091 2019, . 1093 [RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and 1094 T. Voelker, "Packetization Layer Path MTU Discovery for 1095 Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, 1096 September 2020, . 1098 Appendix A. Example Of An Encapsulated IP Packet Flow 1100 Below an example inner IP packet flow within the encapsulating tunnel 1101 packet stream is shown. Notice how encapsulated IP packets can start 1102 and end anywhere, and more than one or less than 1 may occur in a 1103 single encapsulating packet. 1105 Offset: 0 Offset: 100 Offset: 2900 Offset: 1400 1106 [ ESP1 (1500) ][ ESP2 (1500) ][ ESP3 (1500) ][ ESP4 (1500) ] 1107 [--800--][--800--][60][-240-][--4000----------------------][pad] 1109 Figure 3: Inner and Outer Packet Flow 1111 The encapsulated IP packet flow (lengths include IP header and 1112 payload) is as follows: an 800 octet packet, an 800 octet packet, a 1113 60 octet packet, a 240 octet packet, a 4000 octet packet. 1115 The "BlockOffset" values in the 4 AGGFRAG payload headers for this 1116 packet flow would thus be: 0, 100, 2900, 1400 respectively. The 1117 first encapsulating packet ESP1 has a zero "BlockOffset" which points 1118 at the IP data block immediately following the AGGFRAG header. The 1119 following packet ESP2s "BlockOffset" points inward 100 octets to the 1120 start of the 60 octet data block. The third encapsulating packet 1121 ESP3 contains the middle portion of the 4000 octet data block so the 1122 offset points past its end and into the forth encapsulating packet. 1123 The fourth packet ESP4s offset is 1400 pointing at the padding which 1124 follows the completion of the continued 4000 octet packet. 1126 Appendix B. A Send and Loss Event Rate Calculation 1128 The current best practice indicates that congestion control SHOULD be 1129 done in a TCP friendly way. A TCP friendly congestion control 1130 algorithm is described in [RFC5348]. For this IP-TFS use case (as 1131 with [RFC4342]) the (fixed) packet size is used as the segment size 1132 for the algorithm. The main formula in the algorithm for the send 1133 rate is then as follows: 1135 1 1136 X = ----------------------------------------------- 1137 R * (sqrt(2*p/3) + 12*sqrt(3*p/8)*p*(1+32*p^2)) 1139 Where "X" is the send rate in packets per second, "R" is the round 1140 trip time estimate and "p" is the loss event rate (the inverse of 1141 which is provided by the receiver). 1143 In addition the algorithm in [RFC5348] also uses an "X_recv" value 1144 (the receiver's receive rate). For IP-TFS one MAY set this value 1145 according to the sender's current tunnel send-rate ("X"). 1147 The IP-TFS receiver, having the RTT estimate from the sender can use 1148 the same method as described in [RFC5348] and [RFC4342] to collect 1149 the loss intervals and calculate the loss event rate value using the 1150 weighted average as indicated. The receiver communicates the inverse 1151 of this value back to the sender in the AGGFRAG_PAYLOAD payload 1152 header field "LossEventRate". 1154 The IP-TFS sender now has both the "R" and "p" values and can 1155 calculate the correct sending rate. If following [RFC5348] the 1156 sender should also use the slow start mechanism described therein 1157 when the IP-TFS SA is first established. 1159 Appendix C. Comparisons of IP-TFS 1161 C.1. Comparing Overhead 1163 For comparing overhead the overhead of ESP for both normal and 1164 AGGFRAG tunnel packets must be calculated, and so an algorithm for 1165 encryption and authentication must be chosen. For the data below 1166 AES-GCM-256 was selected. This leads to an IP+ESP overhead of 54. 1168 54 = 20 (IP) + 8 (ESPH) + 2 (ESPF) + 8 (IV) + 16 (ICV) 1170 Additionally, for IP-TFS, non-congestion control AGGFRAG_PAYLOAD 1171 headers were chosen which adds 4 octets for a total overhead of 58. 1173 C.1.1. IP-TFS Overhead 1175 For comparison the overhead of AGGFRAG payload is 58 octets per outer 1176 packet. Therefore the octet overhead per inner packet is 58 divided 1177 by the number of outer packets required (fractional allowed). The 1178 overhead as a percentage of inner packet size is a constant based on 1179 the Outer MTU size. 1181 OH = 58 / Outer Payload Size / Inner Packet Size 1182 OH % of Inner Packet Size = 100 * OH / Inner Packet Size 1183 OH % of Inner Packet Size = 5800 / Outer Payload Size 1185 Type IP-TFS IP-TFS IP-TFS 1186 MTU 576 1500 9000 1187 PSize 518 1442 8942 1188 ------------------------------- 1189 40 11.20% 4.02% 0.65% 1190 576 11.20% 4.02% 0.65% 1191 1500 11.20% 4.02% 0.65% 1192 9000 11.20% 4.02% 0.65% 1194 Figure 4: IP-TFS Overhead as Percentage of Inner Packet Size 1196 C.1.2. ESP with Padding Overhead 1198 The overhead per inner packet for constant-send-rate padded ESP 1199 (i.e., traditional IPsec TFC) is 36 octets plus any padding, unless 1200 fragmentation is required. 1202 When fragmentation of the inner packet is required to fit in the 1203 outer IPsec packet, overhead is the number of outer packets required 1204 to carry the fragmented inner packet times both the inner IP overhead 1205 (20) and the outer packet overhead (54) minus the initial inner IP 1206 overhead plus any required tail padding in the last encapsulation 1207 packet. The required tail padding is the number of required packets 1208 times the difference of the Outer Payload Size and the IP Overhead 1209 minus the Inner Payload Size. So: 1211 Inner Paylaod Size = IP Packet Size - IP Overhead 1212 Outer Payload Size = MTU - IPsec Overhead 1214 Inner Payload Size 1215 NF0 = ---------------------------------- 1216 Outer Payload Size - IP Overhead 1218 NF = CEILING(NF0) 1220 OH = NF * (IP Overhead + IPsec Overhead) 1221 - IP Overhead 1222 + NF * (Outer Payload Size - IP Overhead) 1223 - Inner Payload Size 1225 OH = NF * (IPsec Overhead + Outer Payload Size) 1226 - (IP Overhead + Inner Payload Size) 1228 OH = NF * (IPsec Overhead + Outer Payload Size) 1229 - Inner Packet Size 1231 C.2. Overhead Comparison 1233 The following tables collect the overhead values for some common L3 1234 MTU sizes in order to compare them. The first table is the number of 1235 octets of overhead for a given L3 MTU sized packet. The second table 1236 is the percentage of overhead in the same MTU sized packet. 1238 XXX rerun these. 1240 Type ESP+Pad ESP+Pad ESP+Pad IP-TFS IP-TFS IP-TFS 1241 L3 MTU 576 1500 9000 576 1500 9000 1242 PSize 522 1446 8946 518 1442 8942 1243 ----------------------------------------------------------- 1244 40 482 1406 8906 4.5 1.6 0.3 1245 128 394 1318 8818 14.3 5.1 0.8 1246 256 266 1190 8690 28.7 10.3 1.7 1247 518 4 928 8428 58.0 20.8 3.4 1248 576 576 870 8370 64.5 23.2 3.7 1249 1442 286 4 7504 161.5 58.0 9.4 1250 1500 228 1500 7446 168.0 60.3 9.7 1251 8942 1426 1558 4 1001.2 359.7 58.0 1252 9000 1368 1500 9000 1007.7 362.0 58.4 1254 Figure 5: Overhead comparison in octets 1256 Type ESP+Pad ESP+Pad ESP+Pad IP-TFS IP-TFS IP-TFS 1257 MTU 576 1500 9000 576 1500 9000 1258 PSize 522 1446 8946 518 1442 8942 1259 ----------------------------------------------------------- 1260 40 1205.0% 3515.0% 22265.0% 11.20% 4.02% 0.65% 1261 128 307.8% 1029.7% 6889.1% 11.20% 4.02% 0.65% 1262 256 103.9% 464.8% 3394.5% 11.20% 4.02% 0.65% 1263 518 0.8% 179.2% 1627.0% 11.20% 4.02% 0.65% 1264 576 100.0% 151.0% 1453.1% 11.20% 4.02% 0.65% 1265 1442 19.8% 0.3% 520.4% 11.20% 4.02% 0.65% 1266 1500 15.2% 100.0% 496.4% 11.20% 4.02% 0.65% 1267 8942 15.9% 17.4% 0.0% 11.20% 4.02% 0.65% 1268 9000 15.2% 16.7% 100.0% 11.20% 4.02% 0.65% 1270 Figure 6: Overhead as Percentage of Inner Packet Size 1272 C.3. Comparing Available Bandwidth 1274 Another way to compare the two solutions is to look at the amount of 1275 available bandwidth each solution provides. The following sections 1276 consider and compare the percentage of available bandwidth. For the 1277 sake of providing a well understood baseline normal (unencrypted) 1278 Ethernet as well as normal ESP values are included. 1280 C.3.1. Ethernet 1282 In order to calculate the available bandwidth the per packet overhead 1283 is calculated first. The total overhead of Ethernet is 14+4 octets 1284 of header and CRC plus and additional 20 octets of framing (preamble, 1285 start, and inter-packet gap) for a total of 38 octets. Additionally 1286 the minimum payload is 46 octets. 1288 Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP 1289 MTU 590 1514 9014 590 1514 9014 any any 1290 OH 92 92 92 96 96 96 38 74 1291 ------------------------------------------------------------ 1292 40 614 1538 9038 47 42 40 84 114 1293 128 614 1538 9038 151 136 129 166 202 1294 256 614 1538 9038 303 273 258 294 330 1295 518 614 1538 9038 614 552 523 574 610 1296 576 1228 1538 9038 682 614 582 614 650 1297 1442 1842 1538 9038 1709 1538 1457 1498 1534 1298 1500 1842 3076 9038 1777 1599 1516 1538 1574 1299 8942 11052 10766 9038 10599 9537 9038 8998 9034 1300 9000 11052 10766 18076 10667 9599 9096 9038 9074 1302 Figure 7: L2 Octets Per Packet 1304 Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP 1305 MTU 590 1514 9014 590 1514 9014 any any 1306 OH 92 92 92 96 96 96 38 74 1307 -------------------------------------------------------------- 1308 40 2.0M 0.8M 0.1M 26.4M 29.3M 30.9M 14.9M 11.0M 1309 128 2.0M 0.8M 0.1M 8.2M 9.2M 9.7M 7.5M 6.2M 1310 256 2.0M 0.8M 0.1M 4.1M 4.6M 4.8M 4.3M 3.8M 1311 518 2.0M 0.8M 0.1M 2.0M 2.3M 2.4M 2.2M 2.1M 1312 576 1.0M 0.8M 0.1M 1.8M 2.0M 2.1M 2.0M 1.9M 1313 1442 678K 812K 138K 731K 812K 857K 844K 824K 1314 1500 678K 406K 138K 703K 781K 824K 812K 794K 1315 8942 113K 116K 138K 117K 131K 138K 139K 138K 1316 9000 113K 116K 69K 117K 130K 137K 138K 137K 1318 Figure 8: Packets Per Second on 10G Ethernet 1320 Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP 1321 590 1514 9014 590 1514 9014 any any 1322 92 92 92 96 96 96 38 74 1323 ---------------------------------------------------------------------- 1324 40 6.51% 2.60% 0.44% 84.36% 93.76% 98.94% 47.62% 35.09% 1325 128 20.85% 8.32% 1.42% 84.36% 93.76% 98.94% 77.11% 63.37% 1326 256 41.69% 16.64% 2.83% 84.36% 93.76% 98.94% 87.07% 77.58% 1327 518 84.36% 33.68% 5.73% 84.36% 93.76% 98.94% 93.17% 87.50% 1328 576 46.91% 37.45% 6.37% 84.36% 93.76% 98.94% 93.81% 88.62% 1329 1442 78.28% 93.76% 15.95% 84.36% 93.76% 98.94% 97.43% 95.12% 1330 1500 81.43% 48.76% 16.60% 84.36% 93.76% 98.94% 97.53% 95.30% 1331 8942 80.91% 83.06% 98.94% 84.36% 93.76% 98.94% 99.58% 99.18% 1332 9000 81.43% 83.60% 49.79% 84.36% 93.76% 98.94% 99.58% 99.18% 1334 Figure 9: Percentage of Bandwidth on 10G Ethernet 1336 A sometimes unexpected result of using an AGGFRAG tunnel (or any 1337 packet aggregating tunnel) is that, for small to medium sized 1338 packets, the available bandwidth is actually greater than native 1339 Ethernet. This is due to the reduction in Ethernet framing overhead. 1340 This increased bandwidth is paid for with an increase in latency. 1341 This latency is the time to send the unrelated octets in the outer 1342 tunnel frame. The following table illustrates the latency for some 1343 common values on a 10G Ethernet link. The table also includes 1344 latency introduced by padding if using ESP with padding. 1346 ESP+Pad ESP+Pad IP-TFS IP-TFS 1347 1500 9000 1500 9000 1349 ------------------------------------------ 1350 40 1.12 us 7.12 us 1.17 us 7.17 us 1351 128 1.05 us 7.05 us 1.10 us 7.10 us 1352 256 0.95 us 6.95 us 1.00 us 7.00 us 1353 518 0.74 us 6.74 us 0.79 us 6.79 us 1354 576 0.70 us 6.70 us 0.74 us 6.74 us 1355 1442 0.00 us 6.00 us 0.05 us 6.05 us 1356 1500 1.20 us 5.96 us 0.00 us 6.00 us 1358 Figure 10: Added Latency 1360 Notice that the latency values are very similar between the two 1361 solutions; however, whereas IP-TFS provides for constant high 1362 bandwidth, in some cases even exceeding native Ethernet, ESP with 1363 padding often greatly reduces available bandwidth. 1365 Appendix D. Acknowledgements 1367 We would like to thank Don Fedyk for help in reviewing and editing 1368 this work. We would also like to thank Michael Richardson, Sean 1369 Turner and Valery Smyslov for reviews and many suggestions for 1370 improvements, as well as Joseph Touch for the transport area review 1371 and suggested improvements. 1373 Appendix E. Contributors 1375 The following people made significant contributions to this document. 1377 Lou Berger 1378 LabN Consulting, L.L.C. 1380 Email: lberger@labn.net 1382 Author's Address 1384 Christian Hopps 1385 LabN Consulting, L.L.C. 1387 Email: chopps@chopps.org