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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-10) exists of draft-ietf-behave-lsn-requirements-01 == Outdated reference: A later version (-07) exists of draft-ietf-intarea-ipv4-id-update-02 == Outdated reference: A later version (-03) exists of draft-wing-nat-reveal-option-01 -- Obsolete informational reference (is this intentional?): RFC 5201 (Obsoleted by RFC 7401) Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Boucadair 3 Internet-Draft France Telecom 4 Intended status: Informational J. Touch 5 Expires: December 16, 2011 USC/ISI 6 P. Levis 7 France Telecom 8 R. Penno 9 Juniper Networks 10 June 14, 2011 12 Analysis of Solution Candidates to Reveal a Host Identifier in Shared 13 Address Deployments 14 draft-boucadair-intarea-nat-reveal-analysis-03 16 Abstract 18 This document analyzes a set of solution candidates which have been 19 proposed to mitigate some of the issues encountered when address 20 sharing is used. In particular, this document focuses on means to 21 reveal a host identifier when a Carrier Grade NAT (CGN) is involved 22 in the path. This host identifier must be unique to each host under 23 the same shared IP address. 25 The ultimate goal is to assess the viability of proposed solutions 26 and hopefully to make a recommendation on the more suitable 27 solution(s). 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC2119]. 35 Status of this Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at http://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on December 16, 2011. 51 Copyright Notice 53 Copyright (c) 2011 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 1.1. Problem to Be Solved . . . . . . . . . . . . . . . . . . . 4 70 1.2. HOST_ID and Privacy . . . . . . . . . . . . . . . . . . . 5 71 1.3. Purpose and Scope . . . . . . . . . . . . . . . . . . . . 6 72 2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 6 73 3. Solutions Analysis . . . . . . . . . . . . . . . . . . . . . . 8 74 3.1. Define an IP Option . . . . . . . . . . . . . . . . . . . 8 75 3.1.1. Description . . . . . . . . . . . . . . . . . . . . . 9 76 3.1.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 9 77 3.2. Define a TCP Option . . . . . . . . . . . . . . . . . . . 9 78 3.2.1. Description . . . . . . . . . . . . . . . . . . . . . 9 79 3.2.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 9 80 3.3. Use the Identification Field of IP Header (IP-ID) . . . . 10 81 3.3.1. Description . . . . . . . . . . . . . . . . . . . . . 10 82 3.3.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 10 83 3.4. Inject Application Headers . . . . . . . . . . . . . . . . 11 84 3.4.1. Description . . . . . . . . . . . . . . . . . . . . . 11 85 3.4.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 11 86 3.5. PROXY Protocol . . . . . . . . . . . . . . . . . . . . . . 12 87 3.5.1. Description . . . . . . . . . . . . . . . . . . . . . 12 88 3.5.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 12 89 3.6. Enforce a Source-based Selection Algorithm at the 90 Server Side (Port Set) . . . . . . . . . . . . . . . . . . 12 91 3.6.1. Description . . . . . . . . . . . . . . . . . . . . . 13 92 3.6.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 13 93 3.7. Host Identity Protocol (HIP) . . . . . . . . . . . . . . . 13 94 3.7.1. Description . . . . . . . . . . . . . . . . . . . . . 13 95 3.7.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 13 96 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 97 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 98 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 99 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 100 7.1. Normative References . . . . . . . . . . . . . . . . . . . 14 101 7.2. Informative References . . . . . . . . . . . . . . . . . . 15 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 104 1. Introduction 106 As reported in [I-D.ietf-intarea-shared-addressing-issues], several 107 issues are encountered when an IP address is shared among several 108 subscribers. Examples of such issues are listed below: 110 o Implicit identification (Section 13.2 of 111 [I-D.ietf-intarea-shared-addressing-issues]) 113 o SPAM (Section 13.3 of [I-D.ietf-intarea-shared-addressing-issues]) 115 o Blacklisting a mis-behaving user (Section 13.1 of 116 [I-D.ietf-intarea-shared-addressing-issues]) 118 o Redirect users with infected machines to a dedicated portal 119 (Section 5.1 of [I-D.ietf-intarea-shared-addressing-issues]) 121 The sole use of the IPv4 address is not sufficient to uniquely 122 distinguish a host. As a mitigation, it is tempting to investigate 123 means which would help in disclosing an information to be used by the 124 remote server as a means to uniquely disambiguate packets of hosts 125 using the same IPv4 address. 127 1.1. Problem to Be Solved 129 Observation: Today, servers use the source IPv4 address as an 130 identifier to treat some incoming connections differently. Tomorrow, 131 due to the introduction of CGNs (e.g., NAT44 132 [I-D.ietf-behave-lsn-requirements], NAT64 [RFC6146]), that address 133 will be shared. In particular, when a server receives packets from 134 the same source address. Because this address is shared, the server 135 does not know which host is the sending host. 137 Objective: The server should be able to sort out the packets by 138 sending host. 140 Requirement: The server must have extra information than the source 141 IP address to differentiate the sending host. We call HOST_ID this 142 information. 144 For all solutions analyzed, we provide answers to the following 145 questions: 147 o What is the HOST_ID? It must be unique to each host under the 148 same address. It does not need to be globally unique. Of course, 149 the combination of the (public) IPv4 source address and the 150 identifier ends up being relatively unique. As unique as today's 151 32-bit IPv4 addresses which, today, can change when a host re- 152 connects. 154 o Where is the HOST_ID? (which protocol, which field): If the 155 HOST_ID is put at the IP level, all packets will have to bear the 156 identifier. If it is put at a higher connection-oriented level, 157 the identifier is only needed once in the session establishment 158 phase (for instance TCP three-way-handshake), then, all packets 159 received in this session will be attributed to the HOST_ID 160 designated during the session opening. 162 o Who puts the HOST_ID?: For almost all the analyzed solutions, the 163 address sharing function injects the HOST_ID. When there are 164 several address sharing functions in the data path, we describe to 165 what extent the proposed solution is efficient. Another option to 166 avoid potential performance degradation is to let the host inject 167 its HOST_ID but the address sharing function will check its 168 content (just like an IP anti-spoofing function). 170 o What are the security considerations?: Security consideration are 171 common to all analyzed solutions (see Section 5). 173 1.2. HOST_ID and Privacy 175 The HOST_ID does not reveal the identity of a user but provide an 176 information to be used to uniquely identify a host among those 177 sharing the same IP address. 179 The HOST_ID does not reveal more privacy information than what the 180 source IP address does in a non-shared address environment. 182 The volatility of the HOST_ID information is similar the source IP 183 address: a distinct HOST_ID may be used by the address sharing 184 function when the host reboots or gets a new internal IP address. 186 The trust on the information conveyed in the HOST_ID is the same as 187 for current practices with the source IP address. In that sense, a 188 HOST_ID can be spoofed as this is also the case for the spoofing of 189 the IP address. 191 It is of the responsibility of the remote server to rely or not on 192 the content of the HOST_ID to enforce its policies and to log or not 193 the content conveyed in the HOST_ID. 195 For content providers requiring strong security, enabling explicit 196 authentication means and adequate security suite is more robust than 197 relying on source IP address or HOST_ID. 199 1.3. Purpose and Scope 201 The purpose of this document is to analyze the solutions that have 202 been proposed so far and to assess to what extent they solve the 203 problem (see Section 1.1). 205 Note that similar issues may be encountered in an IPv6 environment 206 also (e.g., when the same /64 is used among several hosts). 208 The purpose of this document is not to argue in favor of mandating 209 the use of a HOST_ID but to document encountered issues, proposed 210 solutions and their limitations. 212 Only IPv4-based solutions are analyzed in the following sections: 213 define a new IP option (Section 3.1), define a new TCP option 214 (Section 3.2), use the Identification field of IP header (denoted as 215 IP-ID, Section 3.3), inject application headers (Section 3.4), enable 216 Proxy Protocol Section 3.5, use of port set (Section 3.6) and 217 activate HIP (Section 3.7). 219 2. Recommendations 221 The following Table 1 summarizes the approaches analyzed in this 222 document. 224 o "Success ratio" indicates the ratio of successful communications 225 when the option is used. Provided figures are inspired from the 226 results documented in [Options]. 228 o "Deployable today" indicates if the solution can be generalized 229 without any constraint on current architectures and practices. 231 +-------+-------+-------+--------+----------+------+-----+ 232 | IP | TCP | IP-ID | HTTP | Proxy | Port | HIP | 233 | Option| Option| | Header | Protocol | Set | | 234 | | | | (XFF) | | | | 235 ----------+-------+-------+-------+--------+----------+------+-----+ 236 UDP | Yes | No | Yes | No | No | Yes | | 237 ----------+-------+-------+-------+--------+----------+------+-----+ 238 TCP | Yes | Yes | Yes | No | Yes | Yes | | 239 ----------+-------+-------+-------+--------+----------+------+-----+ 240 HTTP | Yes | Yes | Yes | Yes | Yes | Yes | | 241 ----------+-------+-------+-------+--------+----------+------+-----+ 242 Encrypted | Yes | Yes | Yes | No | Yes | Yes | | 243 Traffic | | | | | | | | 244 ----------+-------+-------+-------+--------+----------+------+-----+ 245 Success | 30% | 99% | 100% | 100% | Low | 100% |Low | 246 Ratio | | | | | | | | 247 ----------+-------+-------+-------+--------+----------+------+-----+ 248 Possible | High | Med | Low | Med | High | No | N/A | 249 Perf | | to | to | to | | | | 250 Impact (6)| | High | Med | High | | | | 251 ----------+-------+-------+-------+--------+----------+------+-----+ 252 OS TCP/IP | Yes | Yes | Yes | No | No | No | | 253 Modif (7) | | | | | | | | 254 ----------+-------+-------+-------+--------+----------+------+-----+ 255 Deployable| Yes | Yes | Yes | Yes | No | Yes | No | 256 Today | | | | | | | | 257 ----------+-------+-------+-------+--------+----------+------+-----+ 258 Notes | | | (1) | (2) | | (1) | (4) | 259 | | | | | | (3) | (5) | 260 ----------+-------+-------+-------+--------+----------+------+-----+ 262 Table 1: Summary of analyzed solutions. 264 Notes for the above table: 266 (1) Requires mechanism to advertise NAT is participating in this 267 scheme (e.g., DNS PTR record) 269 (2) This solution is widely deployed 271 (3) When the port set is not advertised, the solution is less 272 efficient for third-party services. 274 (4) Requires the client and the server to be HIP-compliant and HIP 275 infrastructure to be deployed. 277 (5) If the client and the server are HIP-enabled, the address 278 sharing function does not need to insert a host-hint. If the 279 client is not HIP-enabled, designing the device that performs 280 address sharing to act as a UDP/TCP-HIP relay is not viable. 282 (6) The rationale behind the indicated potential performance 283 degradation is whether the injection requires some treatment at 284 the IP level or not. 286 (7) The modification is required at the server side. 288 According to the above table and the analysis elaborated in 289 Section 3: 291 o IP Option, IP-ID and Proxy Protocol proposals are broken; 293 o HIP is not largely deployed; 295 o The use of Port Set may contradict the port randomization 296 [RFC6056] requirement identified in 297 [I-D.ietf-intarea-shared-addressing-issues]. This solution can be 298 used by a service provider for the delivery of its own service 299 offerings relying on implicit identification. 301 o XFF is de facto standard deployed and supported in operational 302 networks (e.g., HTTP Severs, Load-Balancers, etc.). 304 o From an application standpoint, the TCP Option is superior to XFF 305 since it is not restricted to HTTP. Nevertheless XFF is 306 compatible with the presence of address sharing and load-balancers 307 in the communication path. To provide a similar functionality, 308 the TCP Option may be extended to allow conveying a list of IP 309 addresses to not loose the source IP address in the presence of 310 load-balancers. Note that TCP Option requires the modification of 311 the OS TCP/IP stack of remote servers; which can be seen as a 312 blocking point. 314 As a conclusion of this analysis, the following recommendation is 315 made: 317 [Hopefully to be completed] 319 3. Solutions Analysis 321 3.1. Define an IP Option 322 3.1.1. Description 324 This proposal aims to define an IP option [RFC0791] to convey a "host 325 identifier". This identifier can be inserted by the address sharing 326 function to uniquely distinguish a host among those sharing the same 327 IP address. The option can convey an IPv4 address, the prefix part 328 of an IPv6 address, etc. 330 Another way for using IP option has been described in Section 4.6 of 331 [RFC3022]. 333 3.1.2. Analysis 335 Unlike the solution presented in Section 3.2, this proposal can apply 336 for any transport protocol. Nevertheless, it is widely known that 337 routers (and other middle boxes) filter IP options. IP packets with 338 IP options can be dropped by some IP nodes. Previous studies 339 demonstrated that "IP Options are not an option" (Refer to 340 [Not_An_Option], [Options]). 342 As a conclusion, using an IP option to convey a host-hint is not 343 viable. 345 3.2. Define a TCP Option 347 3.2.1. Description 349 This proposal [I-D.wing-nat-reveal-option] defines a new TCP option 350 called CX-ID. This option encloses the client's identifier (e.g., an 351 IPv4 address, a subscriber ID, or 64 bits of an IPv6 address). The 352 address sharing device inserts this TCP option to the TCP SYN packet 353 or in the initial ACK. 355 3.2.2. Analysis 357 The risk related to handling a new TCP option is low as measured in 358 [Options]. Using a new TCP option to convey the host-hint does not 359 require any modification to the applications but it is applicable 360 only for TCP-based applications. Applications relying on other 361 transport protocols are therefore left unsolved. 363 Some downsides have been raised against defining a TCP option to 364 reveal a host identity: 366 o Conveying an IP address in a TCP option may be seen as a violation 367 of OSI layers but since IP addresses are already used for the 368 checksum computation, this is not seen as a blocking point. 370 o TCP option space is limited, and might be consumed by the TCP 371 client. [I-D.wing-nat-reveal-option] discusses two approaches to 372 sending the HOST_ID: sending the HOST_ID in the TCP SYN (which 373 consumes more bytes in the TCP header of the TCP SYN) and sending 374 the HOST_ID in a TCP ACK (which consumes only two bytes in the TCP 375 SYN). Content providers may find it more desirable to receive the 376 HOST_ID in the TCP SYN, as that more closely preserves the host 377 hint received in the source IP address as per current practices. 378 It is more complicated to implement sending the HOST_ID in a TCP 379 ACK, as it can introduce MTU issues if the ACK packet also 380 contains TCP data, or a TCP segment is lost. 382 o When there are several NATs in the path, the original HOST_ID may 383 be lost. In such case, the procedure may not be efficient. 385 o Interference with current usages such as X-Forwarded-For (see 386 Section 3.4) should be elaborated to specify the behavior of 387 servers when both options are used; in particular specify which 388 information to use: the content of the TCP option or what is 389 conveyed in the application headers. 391 3.3. Use the Identification Field of IP Header (IP-ID) 393 3.3.1. Description 395 IP-ID (Identification field of IP header) can be used to insert an 396 information which uniquely distinguishes a host among those sharing 397 the same IPv4 address. An address sharing function can re-write the 398 IP-ID field to insert a value unique to the host (16 bits are 399 sufficient to uniquely disambiguate hosts sharing the same IP 400 address). Note that this field is not altered by some NATs; hence 401 some side effects such as counting hosts behind a NAT as reported in 402 [Count]. 404 A variant of this approach relies upon the format of certain packets, 405 such as TCP SYN, where the IP-ID can be modified to contain a 16 bit 406 host-hint. Address sharing devices performing this function would 407 require to indicate they are performing this function out of band, 408 possibly using a special DNS record. 410 3.3.2. Analysis 412 This usage is not compliant with what is recommended in 413 [I-D.ietf-intarea-ipv4-id-update]. 415 [[Touch.NOTE: One other problem - picking an ID value here 416 *requires* coordination, i.e., that no other IP packet with this 417 IP address uses that ID within 2MSL. Unless fragmentation is 418 disabled for all packets all the time, you can't use *any* ID 419 value without that coordination.]] 421 [[Wing.NOTE: Most OSes today are emitting TCP packets with DF=1 422 (OSX, Windows XP and 7, Linux, etc.). So, we can assume the TCP 423 SYN is going to have DF=1, and only insert IP-ID if DF=1 and it's 424 a TCP SYN. Doing that, I don't see any disagreement with Joe's 425 IP-ID document.]] 427 3.4. Inject Application Headers 429 3.4.1. Description 431 Another option is to not require any change at the transport nor the 432 IP levels but to convey at the application payload the required 433 information which will be used to disambiguate hosts. This format 434 and the related semantics depend on its application (e.g., HTTP, SIP, 435 SMTP, etc.). 437 For HTTP, the X-Forwarded-For (XFF) header can be used to display the 438 original IP address when an address sharing device is involved. 439 Service Providers operating address sharing devices can enable the 440 feature of injecting the XFF header which will enclose the original 441 IPv4 address or the IPv6 prefix part. The address sharing device has 442 to strip all included XFF headers before injecting their own. 443 Servers may rely on the contents of this field to enforce some 444 policies such as blacklisting misbehaving users. Note that XFF can 445 also be logged by some servers (this is for instance supported by 446 Apache). 448 3.4.2. Analysis 450 Not all applications impacted by the address sharing can support the 451 ability to disclose the original IP address. Only a subset of 452 protocols (e.g., HTTP) can rely on this solution. 454 For the HTTP case, to prevent users injecting invalid host-hints, an 455 initiative has been launched to maintain a list of trusted ISPs using 456 XFF: See for example the list available at: [Trusted_ISPs] of trusted 457 ISPs as maintained by Wikipedia. If an address sharing device is on 458 the trusted XFF ISPs list, users editing Wikipedia located behind the 459 address sharing device will appear to be editing from their 460 "original" IP address and not from the NATed IP address. If an 461 offending activity is detected, individual hosts can be blacklisted 462 instead of all hosts sharing the same IP address. 464 XFF header injection is a common practice of load balancers. When a 465 load balancer is in the path, the original content of any included 466 XFF header should not be stripped. Otherwise the information about 467 the "origin" IP address will be lost. 469 When several address sharing devices are crossed, XFF header can 470 convey the list of IP addresses. The origin HOST_ID can be exposed 471 to the target server. 473 XFF also introduces some implementation complexity if the HTTP packet 474 is at or close to the MTU size. 476 It has been reported that some "poor" implementation may encounter 477 some parsing issues when injecting XFF header. 479 For encrypted HTTP traffic, injecting XFF header may be broken. 481 3.5. PROXY Protocol 483 3.5.1. Description 485 The solution, referred to as Proxy Protocol [Proxy], does not require 486 any application-specific knowledge. The rationale behind this 487 solution is to prepend each connection with a line reporting the 488 characteristics of the other side's connection as shown in the 489 example below (excerpt from [Proxy]): 491 PROXY TCP4 198.51.100.1 198.51.100.11 56324 443\r\n 493 Upon receipt of a message conveying this line, the server removes the 494 line. The line is parsed to retrieve the transported protocol. The 495 content of this line is recorded in logs and used to enforce 496 policies. 498 3.5.2. Analysis 500 This solution can be deployed in a controlled environment but it can 501 not be deployed to all access services available in the Internet. If 502 the remote server does not support the Proxy Protocol, the session 503 will fail. Other complications will raise due to the presence of 504 firewalls for instance. 506 As a consequence, this solution is broken and can not be recommended. 508 3.6. Enforce a Source-based Selection Algorithm at the Server Side 509 (Port Set) 511 3.6.1. Description 513 This solution proposal does not require any action from the address 514 sharing function to disclose a host identifier. Instead of assuming 515 all the ports are associated with the same host, a random-based 516 algorithm (or any port selection method) is run to generate the set 517 of ports (including the source port of the received packet). The 518 length of the ports set to be generated by the server may be 519 configurable (e.g., 8, 32, 64, 512, 1024, etc.). Instead of a 520 random-based scheme, the server can use contiguous port ranges to 521 form the port sets. 523 The server may reduce (or enlarge) the width of the ports set of the 524 misbehaving action is (not) mitigated. 526 A variant of this proposal is to announce by off-line means the port 527 set assignment policy of an operator. This announcement is not 528 required for the delivery of internal services (i.e., offered by the 529 service provider deploying the address sharing function) relying on 530 implicit identification. 532 3.6.2. Analysis 534 In nominal mode, no coordination is required between the address 535 sharing function and the server side but the efficiency of the method 536 depends on the port set selection algorithm. 538 The method is more efficient if the provider that operates the 539 address sharing device advertises its port assignment policy but this 540 may contradicts the port randomization as identified in 541 [I-D.ietf-intarea-shared-addressing-issues]. 543 The method is deterministic for the delivery of services offered by 544 the service provider offering also the IP connectivity service. 546 3.7. Host Identity Protocol (HIP) 548 3.7.1. Description 550 [RFC5201] specifies an architecture which introduces a new namespace 551 to convey an identity information. 553 3.7.2. Analysis 555 This solution requires both the client and the server to support HIP 556 [RFC5201]. Additional architectural considerations are to be taken 557 into account such as the key exchanges, etc. 559 If the address sharing function is required to act as a UDP/TCP-HIP 560 relay, this is not a viable option. 562 4. IANA Considerations 564 This document does not require any action from IANA. 566 5. Security Considerations 568 The same security concerns apply for the injection of an IP option, 569 TCP option and application-related content (e.g., XFF) by the address 570 sharing device. If the server trusts the content of the HOST_ID 571 field, a third party user can be impacted by a misbehaving user to 572 reveal a "faked" original IP address. 574 6. Acknowledgments 576 Many thanks to D. Wing and C. Jacquenet for their review, comments 577 and inputs. 579 Thanks also to P. McCann, T. Tsou, Z. Dong, B. Briscoe, T. Taylor, M. 580 Blanchet, D. Wing and A. Yourtchenko for the discussions in Prague. 582 Some of the issues related to defining a new TCP option have been 583 raised by L. Eggert. 585 7. References 587 7.1. Normative References 589 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 590 September 1981. 592 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 593 Requirement Levels", BCP 14, RFC 2119, March 1997. 595 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 596 Address Translator (Traditional NAT)", RFC 3022, 597 January 2001. 599 [RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport- 600 Protocol Port Randomization", BCP 156, RFC 6056, 601 January 2011. 603 7.2. Informative References 605 [Count] "A technique for counting NATted hosts", 606 . 608 [I-D.ietf-behave-lsn-requirements] 609 Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A., 610 and H. Ashida, "Common requirements for IP address sharing 611 schemes", draft-ietf-behave-lsn-requirements-01 (work in 612 progress), March 2011. 614 [I-D.ietf-intarea-ipv4-id-update] 615 Touch, J., "Updated Specification of the IPv4 ID Field", 616 draft-ietf-intarea-ipv4-id-update-02 (work in progress), 617 March 2011. 619 [I-D.ietf-intarea-shared-addressing-issues] 620 Ford, M., Boucadair, M., Durand, A., Levis, P., and P. 621 Roberts, "Issues with IP Address Sharing", 622 draft-ietf-intarea-shared-addressing-issues-05 (work in 623 progress), March 2011. 625 [I-D.wing-nat-reveal-option] 626 Yourtchenko, A. and D. Wing, "Revealing hosts sharing an 627 IP address using TCP option", 628 draft-wing-nat-reveal-option-01 (work in progress), 629 February 2011. 631 [Not_An_Option] 632 R. Fonseca, G. Porter, R. Katz, S. Shenker, and I. 633 Stoica,, "IP options are not an option", 2005, . 637 [Options] Alberto Medina, Mark Allman, Sally Floyd, "Measuring 638 Interactions Between Transport Protocols and Middleboxes", 639 2005, . 642 [Proxy] Tarreau, W., "The PROXY protocol", November 2010, . 645 [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson, 646 "Host Identity Protocol", RFC 5201, April 2008. 648 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 649 NAT64: Network Address and Protocol Translation from IPv6 650 Clients to IPv4 Servers", RFC 6146, April 2011. 652 [Trusted_ISPs] 653 "Trusted XFF list", . 656 Authors' Addresses 658 Mohamed Boucadair 659 France Telecom 660 Rennes, 35000 661 France 663 Email: mohamed.boucadair@orange-ftgroup.com 665 Joe Touch 666 USC/ISI 668 Email: touch@isi.edu 670 Pierre Levis 671 France Telecom 672 Caen, 14000 673 France 675 Email: pierre.levis@orange-ftgroup.com 677 Reinaldo Penno 678 Juniper Networks 679 1194 N Mathilda Avenue 680 Sunnyvale, California 94089 681 USA 683 Email: rpenno@juniper.net