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Checking references for intended status: Experimental ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 1063 (Obsoleted by RFC 1191) -- Obsolete informational reference (is this intentional?): RFC 2460 (Obsoleted by RFC 8200) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Hinden 3 Internet-Draft Check Point Software 4 Intended status: Experimental G. Fairhurst 5 Expires: February 10, 2020 University of Aberdeen 6 August 9, 2019 8 IPv6 Minimum Path MTU Hop-by-Hop Option 9 draft-ietf-6man-mtu-option-00 11 Abstract 13 This document specifies a new Hop-by-Hop IPv6 option that is used to 14 record the minimum Path MTU along the forward path between a source 15 to a destination host. This collects a minimum recorded MTU along 16 the path to the destination. The value can then be communicated back 17 to the source using the return Path MTU field in the option. 19 This Hop-by-Hop option is intended to be used in environments like 20 Data Centers and on paths between Data Centers, to allow them to 21 better take advantage of paths able to support a large Path MTU. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on February 10, 2020. 40 Copyright Notice 42 Copyright (c) 2019 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Motivation and Problem Solved . . . . . . . . . . . . . . . . 4 59 3. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 60 4. Applicability Statements . . . . . . . . . . . . . . . . . . 5 61 5. IPv6 Minimum Path MTU Hop-by-Hop Option . . . . . . . . . . . 5 62 6. Router, Host, and Transport Behaviors . . . . . . . . . . . . 6 63 6.1. Router Behaviour . . . . . . . . . . . . . . . . . . . . 6 64 6.2. Host Behavior . . . . . . . . . . . . . . . . . . . . . . 7 65 6.3. Transport Behavior . . . . . . . . . . . . . . . . . . . 9 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 67 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 68 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 69 10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 11 70 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 71 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 72 11.2. Informative References . . . . . . . . . . . . . . . . . 13 73 Appendix A. Planned Experiments . . . . . . . . . . . . . . . . 13 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 76 1. Introduction 78 This draft proposes a new Hop-by-Hop Option to be used to record the 79 minimum MTU along the forward path between the source and destination 80 nodes. The source node creates a packet with this Hop-by-Hop Option 81 and fills the Reported PMTU Field in the option with the value of the 82 MTU for the outbound link that will be used to forward the packet 83 towards the destination. 85 At each subsequent hop where the option is processed, the router 86 compares the value of the Reported PMTU in the option and the MTU of 87 its outgoing link. If the MTU of the outgoing link is less than the 88 Reported PMTU specified in the option, it rewrites the value in the 89 Option Data with the smaller value. When the packet arrives at the 90 Destination node, the Destination node can send the minimum reported 91 PMTU value back to the Source Node using the Return PMTU field in the 92 option. 94 The figure below can be used to illustrate the operation of the 95 method. In this case, the path between the Sender and Destination 96 nodes comprises three links, the sender has a link MTU of size MTU-S, 97 the link between routers R1 and R2 has an MTU of size 8 KBytes, and 98 the final link to the destination has an MTU of size MTU-D. 100 +--------+ +----+ +----+ +-------+ 101 | | | | | | | | 102 | Sender +---------+ R1 +--------+ R2 +-------- + Dest. | 103 | | | | | | | | 104 +--------+ MTU-S +----+ 9000B +----+ MTU-D +-------+ 106 The scenarios are described: 108 Scenario 1, considers all links to have an 9000 Byte MTU and the 109 method is supported by both routers. 111 Scenario 2, considers the destination link to have an MTU of 1500 112 Byte. This is the smallest MTU, router R2 resets the reported PMTU 113 to 1500 Byte and this is detected by the method. Had there been 114 another smaller MTU at a link further along the path that supports 115 the method, the lower PMTU would also have been detected. 117 Scenario 3, considers the case where the router preceding the 118 smallest link does not support the method, and the method then fails 119 to detect the actual PMTU. These scenarios are summarized in the 120 table below. This scenario would also arise if the PTB message was 121 not delivered to the sender. 123 +-+-----+-----+----+----+----------+-----------------------+ 124 | |MTU-S|MTU-D| R1 | R2 | Rec PMTU | Note | 125 +-+-----+-----+----+----+----------+-----------------------+ 126 |1|9000B|9000B| H | H | 9000 B | Endpoints attempt to | 127 | | | | | | use an 9000 B PMTU. | 128 +-+-----+-----+----+----+----------+-----------------------+ 129 |2|9000B|1500B| H | H | 1500 B | Endpoints attempt to | 130 | | | | | | | use a 1500 B PMTU. | 131 +-+-----+-----+----+----+----------+-----------------------+ 132 |3|9000B|1500B| H | - | 9000 B | Endpoints attempt to | 133 | | | | | | | use an 9000 B PMTU, | 134 | | | | | | | but need to implement | 135 | | | | | | | a method to fall back | 136 | | | | | | | use a 1500 B PMTU. | 137 +-+-----+-----+----+----+----------+-----------------------+ 139 IPv6 as specified in [RFC8200] allows nodes to optionally process 140 Hop-by-Hop headers. Specifically from Section 4: 142 o The Hop-by-Hop Options header is not inserted or deleted, but may 143 be examined or processed by any node along a packet's delivery 144 path, until the packet reaches the node (or each of the set of 145 nodes, in the case of multicast) identified in the Destination 146 Address field of the IPv6 header. The Hop-by-Hop Options header, 147 when present, must immediately follow the IPv6 header. Its 148 presence is indicated by the value zero in the Next Header field 149 of the IPv6 header. 151 o NOTE: While [RFC2460] required that all nodes must examine and 152 process the Hop-by-Hop Options header, it is now expected that 153 nodes along a packet's delivery path only examine and process the 154 Hop-by-Hop Options header if explicitly configured to do so. 156 The Hop-by-Hop Option defined in this document is designed to take 157 advantage of this property of how Hop-by-Hop options are processed. 158 Nodes that do not support this Option SHOULD ignore them. This can 159 mean that the value returned in the response message does not account 160 for all links along a path. 162 2. Motivation and Problem Solved 164 The current state of Path MTU Discovery on the Internet is 165 problematic. The problems with the mechanisms defined in [RFC8201] 166 are known to not work well in all environments. Nodes in the middle 167 of the network may not send ICMP Packet Too Big messages or they are 168 rate limited to the point of not making them a useful mechanism. 170 This results in many connection defaulting to 1280 octets and makes 171 it very difficult to take advantage of links with larger MTU where 172 they exist. Applications that need to send large packets over UDP 173 are forced to use IPv6 Fragmentation. 175 Transport encapsulations and network-layer tunnels reduce the PMTU 176 available for a transport to use. For example, Network 177 Virtualization Using Generic Routing Encapsulation (NVGRE) [RFC7637] 178 encapsulates L2 packets in an outer IP header and does not allow IP 179 Fragmentation. 181 The use of 10G Ethernet will not achieve it's potential because the 182 packet per second rate will exceed what most nodes can send to 183 achieve multi-gigabit rates if the packet size limited to 1280 184 octets. For example, the packet per second rate required to reach 185 wire speed on a 10G Ethernet link with 1280 octet packets is about 186 977K packets per second (pps), vs. 139K pps for 9,000 octet packets. 187 A significant difference. 189 The purpose of the this draft is to improve the situation by defining 190 a mechanism that does not rely on nodes in the middle of the network 191 to send ICMPv6 Packet Too Big messages, instead it provides the 192 destination host information on the minimum Path MTU and it can send 193 this information back to the source host. This is expected to work 194 better than the current RFC8201 based mechanisms. 196 3. Requirements Language 198 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 199 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 200 "OPTIONAL" in this document are to be interpreted as described in BCP 201 14 [RFC2119] [RFC8174] when, and only when, they appear in all 202 capitals, as shown here. 204 4. Applicability Statements 206 This Hop-by-Hop Option header is intended to be used in environments 207 such as Data Centers and on paths between Data Centers, to allow them 208 to better take advantage of a path that is able to support a large 209 PMTU. For example, it helps inform a sender that the path includes 210 links that have a MTU of 9,000 Bytes. This has many performance 211 advantages compared to the current practice of limiting packets to 212 1280 Bytes. 214 The design of the option is sufficiently simple that it could be 215 executed on a router's fast path. To create critical mass for this 216 to happen will have to be a strong pull from router vendors 217 customers. This could be the case for connections within and between 218 Data Centers. 220 The method could also be useful in other environments, including the 221 general Internet. 223 5. IPv6 Minimum Path MTU Hop-by-Hop Option 225 The Minimum Path MTU Hop-by-Hop Option has the following format: 227 Option Option Option 228 Type Data Len Data 229 +--------+--------+--------+--------+---------+-------+-+ 230 |BBCTTTTT|00000100| Min-PMTU | Rtn-PMTU |R| 231 +--------+--------+--------+--------+---------+-------+-+ 233 Option Type: 235 BB 00 Skip over this option and continue processing. 237 C 1 Option data can change en route to the packet's final 238 destination. 240 TTTTT nnnnn Option Type assigned from IANA. 242 Length: 4 The size of the each value field in Option Data 243 field supports Path MTU values from 0 to 65,535 octets. 245 Min-PMTU: n 16-bits. The minimum PMTU in octets, reflecting the 246 smallest link MTU that the packet experienced across 247 the path. This is called the Reported PMTU. A value 248 less than the IPv6 minimum link MTU [RFC8200] 249 should be ignored. 251 Rtn-PMTU: n 15-bits. The returned mimimum PMTU, carrying the 15 252 most significant bits of the latest received Min-PMTU 253 field. The value zero means that no Reported MTU is 254 being returned. 256 R n 1-bit. R-Flag. Set by the source to signal that 257 the destination should include the received 258 Reported PMTU in Rtn-PMTU field. 260 NOTE: The encoding of the final two octets (Rtn-PMTU and R-Flag) 261 could be implemented by a mask of the latest received Min-MTU value 262 with 0xFFFE, discarding the right-most bit and then performing a 263 logical 'OR' with the R-Flag value of the sender. 265 6. Router, Host, and Transport Behaviors 267 6.1. Router Behaviour 269 Routers that do not support Hop-by-Hop options SHOULD ignore this 270 option and SHOULD forward the packet. 272 Routers that support Hop-by-Hop Options, but do not recognize this 273 option SHOULD ignore the option and SHOULD forward the packet. 275 Routers that recognize this option SHOULD compare the Reported PMTU 276 in the Min-PMTU field and the MTU configured for the outgoing link. 277 If the MTU of the outgoing link is less than the Reported PMTU, the 278 router rewrites the Reported PMTU in the Option to use the smaller 279 value. 281 The router MUST ignore and not change the Rtn-PMTU field and R-Flag 282 in the option. 284 Discussion: 286 o The design of this Hop-by-Hop Option makes it feasible to be 287 implemented within the fast path of a router, because the required 288 processing is simple. 290 6.2. Host Behavior 292 The source host that supports this option SHOULD create a packet with 293 this Hop-by-Hop Option and fill the Min-PMTU field of the option with 294 the MTU of configured for the link over which it will send the packet 295 on the next hop towards the destination. 297 The source host may request that the destination host return the 298 received minimum MTU value by setting the R-Flag in the option. This 299 will cause the destination host to include a PMTU option in an 300 outgoing packet. 302 Discussion: 304 o This option does not need to be sent in all packets belonging to a 305 flow. A transport protocol (or packetization layer) can set this 306 option only on specific packets used to test the path. 308 o In the case of TCP, the option could be included in packets 309 carrying a SYN segment as part of the connection set up, or can 310 periodically be sent in packets carrying other segments. 311 Including this packet in a SYN could increase the probability that 312 SYN segment is lost, when routers on the path drop packets with 313 this option. Including this option in a large packet is not 314 likely to be useful, since the large packet might itself also be 315 dropped by a link along the path with a smaller MTU, preventing 316 the Reported PMTU information from reaching the Destination node. 318 o The use with datagram transport protocols (e.g. UDP) is harder to 319 characterize because applications using datagram transports range 320 from very short-lived (low data-volume applications) exchanges, to 321 longer (bulk) exchanges of packets between the Source and 322 Destination nodes [RFC8085]. 324 o For applications that use Anycast, this option should be included 325 in all packets as the actual destination will vary due to the 326 nature of Anycast. 328 o Simple-exchange protocols (i.e low data-volume applications 329 [RFC8085] that only send one or a few packets per transaction, 330 could be optimized by assuming that the Path MTU is symmetrical, 331 that is where the Path MTU is the same in both directions, or at 332 least not smaller in the return path. This optimisation does not 333 hold when the paths are not symmetric. 335 o The use of this option with DNS and DNSSEC over UDP ought to work 336 as long as the paths are symmetric. The DNS server will learn the 337 Path MTU from the DNS query messages. If the return Path MTU is 338 smaller, then the large DNSSEC response may be dropped and the 339 known problems with PMTUD will occur. DNS and DNSSEC over 340 transport protocols that can carry the Path MTU should work. 342 The Source Host can request the destination host to send a packet 343 carrying the PMTU Option using the R-Flag. 345 A Destination Host SHOULD respond to each packet received with the 346 R-Flag set, by setting the PMTU Option in the next packet that it 347 sends to the Source Host by the same upper layer protocol instance. 349 The upper layer protocol MAY generate a packet when any of these 350 conditions is met when the R Flag is set in the PMTU Option and 351 either: 353 o It is the first Reported PMTU value it has received from the 354 Source. 356 o The Reported PMTU value is lower than previously received. 358 The R-Flag SHOULD NOT be set when the PMTU Option was sent solely to 359 carry the feedback of a Reported PMTU. 361 The PMTU Option sent back to the source SHOULD contain the outgoing 362 link MTU in Min-PMTU field and SHOULD set the last Received PMTU in 363 the Rtn-PMTU field. If these values are not present the field MUST 364 be set to zero. 366 For a connection-oriented upper layer protocol, this could be 367 implemented by saving the value of the last received option within 368 the connection context. This last received value is then used to set 369 the return Path MTU field for all packets belonging to this flow that 370 carry the IPv6 Minimum Path MTU Hop-by-Hop Option. 372 A connection-less protocol, e.g., based on UDP, requires the 373 application to be updated to cache the Received PMTU value, and to 374 ensure that this corresponding value is used to set the last Received 375 PMTU in the Rtn-PMTU field of any PMTU Option that it sends. 377 NOTE: The Rtn-PMTU value is specific to the instance of the upper 378 layer protocol (i.e. matching the IPv6 flow ID, port-fields in UDP or 379 the SPI in IPsec, etc), not the protocol itself, because network 380 devices can make forwarding decisions that impact the PMTU based on 381 the presence and values of these upper layer fields, and therefore 382 these fields need to correspond to those of the packets for the flow 383 received by the Destination Host set to ensure feedback is provided 384 to the corresponding Source Host. 386 NOTE: An upper layer protocol that send packets from the Destination 387 Host towards the Source Host less frequently than the Destination 388 Host receives packets from the Source Host, provides less frequent 389 feedback of the received Min-PMTU value. However, it will always 390 needs to send the most recent value. 392 Discussion: 394 o A simple mechanism could only send an MTU Option with the Rtn-PMTU 395 field filled in the first time this option is received or when the 396 Received PMTU is reduced. This is good because it limits the 397 number sent, but there is no provision for retransmission of the 398 PMTU Option fails to reach the sender, or the sender looses state. 400 o The Reported PMTU value could increase or decrease over time. For 401 instance, it would increase when the path changes and the packets 402 become then forwarded over a link with a MTU larger than the link 403 previously used. 405 6.3. Transport Behavior 407 A transport endpoint using this option needs to use a method to 408 verify the information provided by this option. 410 The Received PMTU does not necessarily reflect the actual PMTU 411 between the sender and destination. Care therefore needs to be 412 exercised in using this value at the sender. Specifically: 414 o If the Received PMTU value returned by the Destination is the same 415 as the initial Reported PMTU value, there could still be a router 416 or layer 2 device on the path that does not support this PMTU. 417 The usable PMTU therefore needs to be confirmed. 419 o If the Received PMTU value returned by the Destination is smaller 420 than the initial Reported PMTU value, this is an indication that 421 there is at least one router in the path with a smaller MTU. 422 There could still be another router or layer 2 device on the path 423 that does not support this MTU. 425 o If the Received PMTU value returned by the Destination is larger 426 than the initial Reported PMTU value, this may be a corrupted, 427 delayed or mis-ordered response, and SHOULD be ignored. 429 A sender needs to discriminate between the Received PMTU value in a 430 PTB message generated in response to a Hop-by-Hop option requesting 431 this, and a PTB message received from a router on the path. 433 A PMTUD or PLPMTUD method could use the Received PMTU value as an 434 initial target size to probe the path. This can significantly 435 decrease the number of probe attempts (and hence time taken) to 436 arrive at a workable PMTU. It has the potential to complete 437 discovery of the correct value in a single Round Trip Time (RTT), 438 even over paths that may have successive links configured with lower 439 MTUs. 441 Since the method can delay notification of an increase in the actual 442 PMTU, a sender with a link MTU larger than the current PMTU SHOULD 443 periodically probe for a PMTU value that is larger than the Received 444 PMTU value. This specification does not define an interval for the 445 time between probes. 447 Since the option consumes less capacity than an a full probe packet, 448 there may be advantage in using this to detect a change in the path 449 characteristics. 451 NOTE: Further details to be included in next version. 453 NOTE: A future version of the document will consider more the impact 454 of Equal Cost Multipath (ECMP). Specifically, whether a Received 455 PMTU value should be maintained by the method for each transport 456 endpoint, or for each network address, and how these are best used by 457 methods such as PLPMTUD or DPLPMTUD. 459 7. IANA Considerations 461 IANA is requested to assign and register a new IPv6 Hop-by-Hop Option 462 type from the "Destination Options and Hop-by-Hop Options" registry 463 [IANA-HBH] as shown in Section 5. This assignment should have the 464 "act" and "chg" bits set to 00 and 1. 466 8. Security Considerations 468 The method has no way to protect the destination from off-path attack 469 using this option in packets that do not originate from the source. 470 This attack could be used to inflate or reduce the size of the 471 reported PMTU. Mechanisms to provide this protection can be provided 472 at a higher layer (e.g., the transport packetization layer using 473 PLPMTUD or DPLPMTUD), where more information is available about the 474 size of packet that has successfully traversed a path. 476 The method solicits a response from the destination, which should be 477 used to generate a response to the IPv6 node originating the option 478 packet. A malicious attacker could generate a packet to the 479 destination for a previously inactive flow or one that advertises a 480 change in the size of the MTU for an active flow. This would create 481 additional work at the destination, and could induce creation of 482 state when a new flow is created. It could potentially result in 483 additional traffic on the return path to the sender, which could be 484 mitigated by limiting the rate at which responses are generated. 486 A sender MUST check the quoted packet within the PTB message to 487 validate that the message is in response to a packet that was 488 originated by the sender. This is intended to provide protection 489 against off-path insertion of ICMP PTB messages by an attacker trying 490 to disrupt the service. Messages that fail this check MAY be logged, 491 but the information they contain MUST be discarded. 493 TBD 495 9. Acknowledgments 497 A somewhat similar mechanism was proposed for IPv4 in 1988 in 498 [RFC1063] by Jeff Mogul, C. Kent, Craig Partridge, and Keith 499 McCloghire. It was later obsoleted in 1990 by [RFC1191] the current 500 deployed approach to Path MTU Discovery. 502 Helpful comments were received from Tom Herbert, Tom Jones, Fred 503 Templin, Ole Troan, [Your name here], and other members of the 6MAN 504 working group. 506 10. Change log [RFC Editor: Please remove] 508 draft-ietf-6man-mtu-option-00, 2019-August-9 510 o First 6man w.g. draft version. 511 o Changes to request IANA allocation of code point. 512 o Editorial changes. 514 draft-hinden-6man-mtu-option-02, 2019-July-5 516 o Changed option format to also include the Returned MTU value and 517 Return flag and made related text changes in Section 6.2 to 518 describe this behaviour. 519 o ICMP Packet Too Big messages are no longer used for feedback to 520 the Source host. 521 o Added to Acknowledgements Section that a similar mechanism was 522 proposed for IPv4 in 1988 in [RFC1063]. 523 o Editorial changes. 525 draft-hinden-6man-mtu-option-01, 2019-March-05 527 o Changed requested status from Standards Track to Experimental to 528 allow use of experimental option type (11110) to allow for 529 experimentation. Removed request for IANA Option assignment. 530 o Added Section 2 "Motivation and Problem Solved" section to better 531 describe what the purpose of this document is. 532 o Added Appendix A describing planned experiments and how the 533 results will be measured. 534 o Editorial changes. 536 draft-hinden-6man-mtu-option-00, 2018-Oct-16 538 o Initial draft. 540 11. References 542 11.1. Normative References 544 [IANA-HBH] 545 "Destination Options and Hop-by-Hop Options", 546 . 549 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 550 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 551 RFC2119, March 1997, . 554 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 555 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 556 May 2017, . 558 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 559 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/ 560 RFC8200, July 2017, . 563 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 564 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 565 DOI 10.17487/RFC8201, July 2017, . 568 11.2. Informative References 570 [RFC1063] Mogul, J., Kent, C., Partridge, C., and K. McCloghrie, "IP 571 MTU discovery options", RFC 1063, DOI 10.17487/RFC1063, 572 July 1988, . 574 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 575 DOI 10.17487/RFC1191, November 1990, . 578 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 579 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 580 December 1998, . 582 [RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network 583 Virtualization Using Generic Routing Encapsulation", RFC 584 7637, DOI 10.17487/RFC7637, September 2015, 585 . 587 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 588 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 589 March 2017, . 591 Appendix A. Planned Experiments 593 TBD 595 This section will describe a set of experiments planned for the use 596 of the option defined in this document. There are many aspects of 597 the design that require experimental data or experience to evaluate 598 this experimental specification. 600 This includes experiments to understand the pathology of packets sent 601 with the specified option to determine the likelihood that they are 602 lost within specific types of network segment. 604 This includes consideration of the cost and alternatives for 605 providing the feedback required by the mechanism and how to 606 effectively limit the rate of transmission. 608 This includes consideration of the potential for integration in 609 frameworks such as that offered by DPLPMTUD. 611 There are also security-related topics to be understood as described 612 in the Security Considerations (Section 8). 614 Authors' Addresses 616 Robert M. Hinden 617 Check Point Software 618 959 Skyway Road 619 San Carlos, CA 94070 620 USA 622 Email: bob.hinden@gmail.com 624 Godred Fairhurst 625 University of Aberdeen 626 School of Engineering 627 Fraser Noble Building 628 Aberdeen AB24 3UE 629 UK 631 Email: gorry@erg.abdn.ac.uk