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Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 2460 (Obsoleted by RFC 8200) -- Obsolete informational reference (is this intentional?): RFC 2629 (Obsoleted by RFC 7749) -- Obsolete informational reference (is this intentional?): RFC 4960 (Obsoleted by RFC 9260) -- Obsolete informational reference (is this intentional?): RFC 6555 (Obsoleted by RFC 8305) -- Obsolete informational reference (is this intentional?): RFC 6824 (Obsoleted by RFC 8684) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group H. Naderi 3 Internet-Draft B. Carpenter, Ed. 4 Intended status: Informational Univ. of Auckland 5 Expires: October 24, 2015 April 22, 2015 7 Experience with IPv6 path probing 8 draft-naderi-ipv6-probing-01 10 Abstract 12 This document reports on experience and simulations of dynamic 13 probing of alternate paths between two IPv6 hosts when network 14 failures occur. Two models for such probing were investigated: the 15 SHIM6 REAchability Protocol (REAP) and the Multipath Transmission 16 Control Protocol (MPTCP). The motivation for this document is to 17 identify some aspects of path probing at large or very large scale 18 that may be broadly relevant to future protocol design. 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 October 24, 2015. 37 Copyright Notice 39 Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Results for SHIM6 and REAP . . . . . . . . . . . . . . . . . 3 56 2.1. Experiments over the Internet . . . . . . . . . . . . . . 3 57 2.2. Lab Experiments . . . . . . . . . . . . . . . . . . . . . 5 58 2.3. Large scale simulation . . . . . . . . . . . . . . . . . 5 59 3. Results for MPTCP . . . . . . . . . . . . . . . . . . . . . . 7 60 4. Operational issues . . . . . . . . . . . . . . . . . . . . . 8 61 5. Implications for future designs . . . . . . . . . . . . . . . 9 62 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 63 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 64 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 65 9. Change log [RFC Editor: Please remove] . . . . . . . . . . . 10 66 10. Informative References . . . . . . . . . . . . . . . . . . . 10 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 69 1. Introduction 71 A common situation in the Internet today is that a host trying to 72 contact another host has a choice of IP addresses for one or both 73 ends of the communication. Multiple addresses are expected to be 74 quite common for IPv6 hosts [RFC2460]. Some approaches to this 75 situation envisage either switching paths during the course of the 76 communication or using multiple paths in parallel. Examples include 77 "Happy Eyeballs" [RFC6555] which tries alternative paths at the 78 start, SHIM6 [RFC5533] and Stream Control Transmission Protocol 79 (SCTP) [RFC4960] which change paths when there is a failure, and 80 Multipath TCP (MPTCP) [RFC6824] which shares the paths dynamically. 82 Some of these methods involve active path probing to choose the best 83 one. SHIM6 probes all available paths using the REAchability 84 Protocol (REAP) [RFC5534] when the current path fails, and MPTCP 85 effectively probes all paths continuously, and shifts load according 86 to the results. In this document we summarise results and 87 observations from SHIM6 and MPTCP operated or simulated at large 88 scale. These observations may be of help in designing future path 89 probing mechanisms. In particular, we are interested in minimising 90 both the time taken to recover to the maximum possible throughput 91 after a path failure, and the amount of overhead traffic caused by 92 the probing process. 94 In summary, we ran a series of SHIM6 experiments, each including 250 95 path failures, between Auckland and Dublin, measuring the time and 96 overhead traffic for each instance of path probing and recovery. 98 Then we repeated essentially the same experiment in the laboratory in 99 Auckland (i.e., with negligible RTT instead of round-the-world RTT). 100 Then we built a Stochastic Activity Network (SAN) simulation model of 101 the same scenarios, and validated it by comparison with the 102 experimental results. Finally we used this model to simulate path 103 failure and recovery using REAP at very large scale (10,000 104 simultaneous sessions on a single site experiencing path failure). 105 Both TCP and DCCP [RFC4340] were used for the transport layer, with a 106 simple application sending meaningless data in one direction only. 108 This was followed by roughly equivalent simulations of recovery from 109 path failure for MPTCP sessions. In this case we validated the SAN 110 model by comparison with a completely different MPTCP simulator 111 developed elsewhere [Wischik10]. 113 One advantage of the SAN model is that there are SAN analysis 114 software tools which allow very large scale simulations. Another is 115 that it makes it relatively easy to experiment with variations of the 116 protocol itself, so we did test the impact of certain protocol 117 changes. However, unlike conventional network simulation tools, the 118 user has to program a complete protocol behaviour model. We used the 119 Moebius tool [Moebius]. 121 Details of the experiments and results have been described in two 122 papers [Naderi10] [Naderi14b] and in H. Naderi's thesis [Naderi14a]. 123 This document limits itself to outlining the results and their 124 implications for the design of path probing mechanisms in the 125 Internet. 127 2. Results for SHIM6 and REAP 129 2.1. Experiments over the Internet 131 We set up a test environment which enabled us to run a set of 132 experiments over the Internet with the LinShim6 implementation of 133 SHIM6 [Barre08]. We have used two SHIM6-enabled multi- addressed 134 hosts, located in the University of Auckland (New Zealand) and 135 Waterford Institute of Technology (Dublin, Ireland). Each host was 136 equipped with two network interface cards and configured with two 137 prefixes from two different providers. The SHIM6 host in Auckland 138 was connected to a router which was a Linux machine and was 139 configured as an IPv6 router. This router simulated link failures 140 for the experiments. 142 Source Address Dependent Routing (SADR) is necessary for effective 143 use of SHIM6. Hosts decide what source and destination address to 144 use when host-centric solutions, like SHIM6, are used. Without SADR, 145 or similar mechanism for routing, packets might be forwarded to the 146 wrong address providers and dropped because of ingress filtering 147 according to BCP 38 [RFC2827] [RFC3704]. Unfortunately, we could not 148 convince the university network administrators to enable SADR on the 149 Auckland University edge router. To run the experiments, they agreed 150 to add static routes to the edge router's routing table, to forward 151 packets destined to the host in Dublin through different providers 152 according to their destination addresses. Therefore, only two 153 address pairs out of four possible address pairs could work. To 154 resolve this issue, we have changed LinShim6 to shuffle the list of 155 address pairs before starting the exploration process in order to put 156 the working address pair in a random location in the list. As a 157 result, the working address pair could appear in any location in the 158 list and thus create different recovery cases. 160 This configuration enabled us to run experiments with four address 161 pairs over the Internet. For each experiment, we artificially 162 created 250 failures and for each case measured the REAP exploration 163 time (EP), number of sent (SP) and received probes (RP) and 164 application recovery time (ART). 166 Comparing results from experiments with TCP and DCCP shows that when 167 DCCP is employed, EP, SP and RP are bigger than when TCP is used. 168 The main reason for this is that DCCP employs delayed 169 acknowledgement. It sends ACKs every RTT (300 ms), while in case of 170 TCP, they are sent more frequently (less than 100 ms apart). Since 171 the RTT is long, the communications look different from REAP's view 172 point although the behaviour of the application is the same in both 173 experiments. Since TCP sends ACKs faster, REAP treats it more like a 174 bi-directional communication while DCCP communication is treated more 175 like uni-directional. As a result, in the DCCP experiment, the 176 sender always detects the failure first and then reports it to the 177 receiver, while in the TCP experiment both sides detect failure and 178 start exploration almost at the same time. In other words, in case 179 of TCP, exploration is performed in parallel on both sides and takes 180 less time and generates less traffic. This result also shows that 181 the efficiency of the solutions, like SHIM6, which are implemented 182 inside the protocol stack may be affected by the behaviour of the 183 other layers of the protocol stack as well. 185 We also observed some signs of probe loss in the results. Probe 186 losses can affect EP, SP, RP and ART. When a probe is lost, it might 187 cause the exploration process to go to a second round, and then an 188 exponential backoff algorithm causes the exploration process to take 189 longer and generate more traffic. 191 2.2. Lab Experiments 193 We repeated similar experiments in the lab. The main difference was 194 RTT which was much smaller (0.3 ms) than in the Internet experiments. 195 We setup two SHIM6 hosts in the lab, each equipped with four network 196 interfaces. Thus, in addition to experiments with four address pairs 197 (similar to the Internet experiments), we could run experiments with 198 9 and 16 address pairs as well. 200 In the lab, we got similar results from the TCP and DCCP experiments. 201 Since RTT is small, DCCP sends ACKs faster, and therefore there is no 202 difference from REAP's viewpoint. 204 Probe losses are observable in the lab experiments too. Probe loss 205 causes REAP to go to the second round for scanning the list of 206 address pairs, which leads to sending more probes and also longer 207 exploration time. 209 Experiments with 16 address pairs fail when the working address pair 210 is located at or close to the end of the list of address pairs. REAP 211 employs exponential backoff after sending its initial probes, to 212 avoid generating large bursts of traffic during exploration. For 16 213 address pairs, this delay sometimes causes the connection to time out 214 and stop the experiment. In some cases, SHIM6 removes the context 215 without finding the new address pair. In such cases it seems that 216 packet losses cause the exploration process to go to the second round 217 of exploration and the resulting longer delays cause SHIM6 to 218 actually stop exploration and remove the context. 220 2.3. Large scale simulation 222 To study the behaviour of REAP in a very large scale network (e.g., 223 an enterprise network), we built a simulation model of REAP and 224 conducted some experiments which simulated a link failure event in a 225 network with 10,000 simultaneously active SHIM6-monitored 226 communications. The aim of the experiments was to see how REAP 227 reacts to path failures in a large SHIM6-enabled multihomed network. 228 In our practical tests, nine address pairs seems to be the limit but 229 we have included larger numbers in our simulations to obtain a 230 clearer view of REAP's behaviour. 232 We focused on REAP recovery time and probe traffic as two important 233 performance parameters. REAP recovery time is the time that REAP 234 takes to detect the failure and find a new working address pair. 235 REAP traffic is the traffic which is generated by REAP itself during 236 its exploration process. 238 We measured average and total REAP recovery time for different 239 numbers of address pairs for 10,000 instances of REAP. We define 240 total REAP recovery time as the recovery time for the whole site, 241 i.e., the time between failure occurrence and recovering the last 242 context. In other words, it shows the recovery time for the last 243 context that is recovered. The average recovery time is calculated 244 by dividing the sum of recovery times for REAP instances by the 245 number of REAP instances. It should be noted that recovery time 246 includes failure detection and address exploration times. 248 A typical average recovery time for 4 address pairs is 10 to 12 249 seconds. The results show that the average and maximum recovery time 250 increase when the number of address pairs is increased. The 251 correlation is not linear because REAP uses an exponential backoff 252 algorithm for increasing the time interval between probes. As a 253 result, REAP shows poor performance when the number of address pairs 254 exceeds 9, for example exceeding 100 seconds to recover with 16 255 address pairs. 257 We also measured the average and total number of probes sent during 258 the address exploration process in the experiments. The results show 259 that there is a linear correlation between number of address pairs 260 and number of sent probes. They also show that a large quantity of 261 probes is sent at the start of exploration. For example, in the case 262 of four address pairs, 93% of the probes, and in the case of 25 263 address pairs 34% of probes, are sent during the first 10 seconds. 264 The reason is that all contexts detect failure within 10 seconds and 265 start exploration by sending initial probes (the first four probes, 266 which are sent in two seconds). After that, there are some intervals 267 when very few probes are sent. This can be seen more clearly in the 268 experiments with more address pairs, e.g. 16 or 25 address pairs. 269 This means that for some SHIM6 contexts the time interval between 270 probes is large, because of the exponential backoff, so REAP 271 instances have to wait for a long time before probing the next 272 address pair. Some connections might be dropped by the transport or 273 application layer before REAP can recover them. For example, in case 274 of 25 address pairs, 50% of contexts need more than five minutes to 275 recover. 277 Although the peak of the REAP traffic is generated in the first 10 278 seconds (before employing the exponential backoff algorithm), our 279 results show that this traffic is small compared to normal traffic 280 for a large network, and cannot cause a major problem. For example, 281 in the case of 25 address pairs, about 4800 probes per second are 282 sent during the first 10 seconds of the exploration process, which is 283 the peak of the traffic. Every probe in the first 10 seconds carries 284 at most seven address pairs; four initial address pairs and three 285 more after employing exponential backoff. Thus, the average probe 286 size in the first 10 seconds is 232 bytes; each probe needs 72 bytes 287 for the fixed part and 40 bytes for each address pair. As a result, 288 a load of 4800 probes per second does not occupy more than one MB/s 289 of the site's available link capacity. Large sites usually have high 290 bandwidth links to the Internet and this amount of traffic does not 291 cause a significant problem for them. In any case this traffic will 292 occur at a time when normal traffic from the same sessions has been 293 interrupted. 295 We also tried two changes to REAP to improve recovery time: 296 Increasing the number of initial probes, and sending initial probes 297 in parallel. In both cases, we also measured the probe traffic. The 298 results showed that those modifications improved recovery time while 299 their effect on the traffic were not big. For example, in case of 300 nine address pairs, increasing the number of initial probes from four 301 to five caused about 6.5% increase in traffic in the first 10 seconds 302 of the recovery process, 22% decrease in average recovery time and 303 34% decrease in maximum recovery time. Sending initial probes in 304 parallel, in the case of nine address pairs, caused an 11% decrease 305 in average recovery time, 4.5% decrease in maximum recovery time, and 306 8.2% increase in traffic. In both cases, these modifications 307 increased traffic but not to the level that could not be handled in a 308 large network. 310 3. Results for MPTCP 312 MPTCP does not use any specific mechanism for probing paths. In 313 fact, every subflow runs as a TCP flow and it is the TCP congestion 314 control mechanism which monitors the used path. When congestion is 315 detected, the load from the congested path is transferred to other 316 available paths, if they present less congestion. The MPCTP 317 congestion control algorithm, known as SEMICOUPLED, reacts to 318 congestion reports from subflows and adjusts the load on the used 319 paths to achieve performance and fairness. TCP never sets the 320 congestion window for a subflow to less than 1. Therefore, even on a 321 highly congested path or a broken path, it performs the equivalent of 322 probing by setting the congestion window size to 1, so that any 323 improvements in the path can be detected. Expiration of the TCP 324 retransmission timer for the subflow on a broken path triggers 325 sending a segment once in a while, acting as a probe, to ensure a 326 recovery in the path can be detected. How fast this mechanism can 327 detect an improvement in a broken path depends on the value of the 328 time-out for this timer (RTO). The minimum value is usually set to 1 329 second and consequent expirations, the case for a broken path, back 330 off the timer value and multiplies RTO by 2. The traffic generated 331 by this mechanism in this case is low and may be handled easily, even 332 in a large network. 334 We simulated MPTCP with up to 8 paths and with RTTs between 80 and 335 150 ms, observing the expected behaviour, with the load in the steady 336 state spread across the paths. When the loss rate of a path is 337 higher, the throughput of that path is lower. For a given loss rate, 338 a smaller RTT increases throughput on that path. However, total 339 throughput increases sublinearly with more paths, due to the way 340 SEMICOUPLED links the congestion windows of the various subflows. 341 For example, we simulated a scenario in which the steady state 342 throughput for 8 paths was only about 25% greater than for a single 343 path (Figure 5.10 in [Naderi14a]). This suggests that a scenario 344 with as many as 8 paths is of limited value in a reasonably reliable 345 network. 347 We simulated a permanent failure of a single path in a scenario with 348 four paths in operation. As may be deduced from the previous point, 349 the throughput recovered in the steady state to within a small 350 percentage of its previous value. This recovery took about 6 seconds 351 (Figure 5.15 in [Naderi14a]), which is significantly faster than 352 observed with SHIM6 due to MPTCP's effectively continuous probing. 353 Simulations of temporary path failures showed that returning to the 354 original steady state using all paths took a similar time. 356 Finally we simulated the effect of variable loss rates on MPTCP 357 performance with two paths operating. We observed that for loss 358 rates varying randomly in the range up to 1%, MPTCP effectively 359 maintains its steady state throughput. 361 4. Operational issues 363 Many if not most site border firewalls today drop packets containing 364 the SHIM6 extension header. In our Internet experiments we had to 365 bypass the site firewall at both ends. This issue is discussed in 366 [RFC7045]. 368 Source Address Dependent Routing (SADR) is necessary for effective 369 use of multiple paths. Without it, packets may be sent to the wrong 370 exit router, or to an ISP that will immediately discard them due to 371 ingress filtering. With ingress filtering in place, packets with a 372 given source address may only be sent via an ISP that accepts packets 373 from that source address. If this is not taken correctly into 374 account by the source host and by the local routing configuration, 375 the host will waste resources trying to explore paths that are 376 certain to fail. 378 5. Implications for future designs 380 We suggest several conclusions from the above results that should be 381 relevant to the design of any probing mechanism for exploiting 382 alternative paths between two hosts: 384 o The interaction between round-trip time, the transport layer 385 acknowledgement mechanism, and the failure detection mechanism is 386 quite subtle and significantly affects the time taken to start 387 recovery after a failure. 389 o When probing is linked to congestion control, packet loss rates 390 may also affect recovery times. 392 o Probe traffic is unlikely to cause overload, especially since 393 normal traffic stops during recovery from failure. 395 o Exponential backoff leads to significantly slower recovery time, 396 and (due to the previous point) is probably unnecessary. 398 o Probing all alternative paths in parallel leads to significantly 399 faster recovery times with only a minor increase in the intensity 400 of probe traffic, although this does occur on the paths that are 401 still carrying normal traffic. However, full sized probe packets 402 (as used by MPTCP, because they are normal data packets) have more 403 impact than short probe packets (as used by SHIM6). 405 o The probe packets should resemble normal data packets as much as 406 possible, in order to avoid being treated specially or dropped by 407 middleboxes such as firewalls or load balancers. 409 o If Source Address Dependent Routing (SADR) is unavailable, it is 410 better to avoid probing address pairs that will fail as a result. 411 (Probing all paths in parallel would in fact mask this problem.) 413 o There is little to be gained by having more than two or three 414 alternative paths. 416 6. Security Considerations 418 Apart from the need for SHIM6 to bypass firewalls, no security issues 419 were identified during this work. 421 7. IANA Considerations 423 This document requests no action by IANA. 425 8. Acknowledgements 427 This document was produced using the xml2rfc tool [RFC2629]. 429 Some text was adapted from [Naderi14a]. 431 John Ronan from the Telecommunications Software and Systems Group, 432 Waterford Institute of Technology, and the University of Auckland 433 Information Technology Services (ITS) helped to run the SHIM6 434 experiments over the Internet between Auckland and Dublin. 436 9. Change log [RFC Editor: Please remove] 438 draft-naderi-ipv6-probing-01: editorial improvements, 2015-04-22. 440 draft-naderi-ipv6-probing-00: original version, 2014-10-21. 442 10. Informative References 444 [Barre08] Barre, S., "LinShim6 - implementation of the Shim6 445 protocol", Technical Report, Universite catholique de 446 Louvain , February 2008. 448 [Moebius] Deavours, D., Clark, G., Courtney, T., Daly, D., Derisavi, 449 S., Doyle, J., Sanders, W., and P. Webster, "The Moebius 450 framework and its implementation", IEEE Transactions on 451 Software Engineering 28(10):956-969, October 2002. 453 [Naderi10] 454 Naderi, H. and B. Carpenter, "A Performance Study on 455 REAchability Protocol in Large Scale IPv6 Networks", 456 Second International Conference on Computer and Network 457 Technology (ICCNT 2010), Bangkok 28-32, April 2010. 459 [Naderi14a] 460 Naderi, H., "Evaluating and Improving SHIM6 and MPTCP: Two 461 Solutions for IPv6 Multihoming", Ph.D. Thesis, The 462 University of Auckland , July 2014. 464 [Naderi14b] 465 Naderi, H. and B. Carpenter, "Putting SHIM6 into 466 Practice", Australasian Telecommunication Networks and 467 Applications Conference (ATNAC 2014), Melbourne , November 468 2014. 470 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 471 (IPv6) Specification", RFC 2460, December 1998. 473 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 474 June 1999. 476 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 477 Defeating Denial of Service Attacks which employ IP Source 478 Address Spoofing", BCP 38, RFC 2827, May 2000. 480 [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed 481 Networks", BCP 84, RFC 3704, March 2004. 483 [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram 484 Congestion Control Protocol (DCCP)", RFC 4340, March 2006. 486 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 487 4960, September 2007. 489 [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming 490 Shim Protocol for IPv6", RFC 5533, June 2009. 492 [RFC5534] Arkko, J. and I. van Beijnum, "Failure Detection and 493 Locator Pair Exploration Protocol for IPv6 Multihoming", 494 RFC 5534, June 2009. 496 [RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with 497 Dual-Stack Hosts", RFC 6555, April 2012. 499 [RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, 500 "TCP Extensions for Multipath Operation with Multiple 501 Addresses", RFC 6824, January 2013. 503 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing 504 of IPv6 Extension Headers", RFC 7045, December 2013. 506 [Wischik10] 507 Wischik, D., Raiciu, C., and M. Handley, "Balancing 508 resource pooling and equipoise in multipath transport", 509 8th USENIX Symposium on Networked Systems Design and 510 Implementation, San Jose , April 2010. 512 Authors' Addresses 513 Habib Naderi 514 Department of Computer Science 515 University of Auckland 516 PB 92019 517 Auckland 1142 518 New Zealand 520 Email: habib@cs.auckland.ac.nz 522 Brian Carpenter (editor) 523 Department of Computer Science 524 University of Auckland 525 PB 92019 526 Auckland 1142 527 New Zealand 529 Email: brian.e.carpenter@gmail.com