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Boucadair 5 Expires: April 1, 2016 France Telecom 6 S. Sivakumar 7 Cisco Systems 8 C. Zhou 9 Huawei Technologies 10 T. Tsou 11 Huawei Technologies (USA) 12 S. Perreault 13 Jive Communications 14 September 29, 2015 16 Port Control Protocol (PCP) Extension for Port Set Allocation 17 draft-ietf-pcp-port-set-10 19 Abstract 21 In some use cases, e.g.,Lightweight 4over6 (lw4o6) [RFC7596], the 22 client may require not just one port, but a port set. This document 23 defines an extension to the Port Control Protocol (PCP) allowing 24 clients to manipulate sets of ports as a whole. This is accomplished 25 by a new MAP option: PORT_SET. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on April 1, 2016. 44 Copyright Notice 46 Copyright (c) 2015 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Applications Using Port Sets . . . . . . . . . . . . . . 3 63 1.2. Lightweight 4over6 . . . . . . . . . . . . . . . . . . . 3 64 1.3. Firewall Control . . . . . . . . . . . . . . . . . . . . 3 65 1.4. Discovering Stateless Port Set Mappings . . . . . . . . . 4 66 2. The need for PORT_SET . . . . . . . . . . . . . . . . . . . . 4 67 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 4. The PORT_SET Option . . . . . . . . . . . . . . . . . . . . . 5 69 4.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 7 70 4.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 7 71 4.3. Absence of Capability Discovery . . . . . . . . . . . . . 8 72 4.4. Port Set Renewal and Deletion . . . . . . . . . . . . . . 8 73 4.4.1. Overlap Conditions . . . . . . . . . . . . . . . . . 8 74 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9 75 5.1. Simple Request on NAT44 . . . . . . . . . . . . . . . . . 9 76 5.2. Stateless Mapping Discovery . . . . . . . . . . . . . . . 10 77 5.3. Resolving Overlap . . . . . . . . . . . . . . . . . . . . 11 78 6. Operational Considerations . . . . . . . . . . . . . . . . . 11 79 6.1. Limits and Quotas . . . . . . . . . . . . . . . . . . . . 11 80 6.2. High Availability . . . . . . . . . . . . . . . . . . . . 12 81 6.3. Idempotence . . . . . . . . . . . . . . . . . . . . . . . 12 82 6.4. What should a PCP client do when it receives fewer ports 83 than requested? . . . . . . . . . . . . . . . . . . . . . 13 84 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 85 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 86 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14 87 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 88 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 89 11.1. Normative References . . . . . . . . . . . . . . . . . . 15 90 11.2. Informative References . . . . . . . . . . . . . . . . . 16 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 93 1. Introduction 95 This document extends PCP [RFC6887] with the ability to retrieve a 96 set of ports using a single request. It does so by defining a new 97 PORT_SET option. 99 This section describes a few (and non-exhaustive) envisioned use 100 cases. Note that the PCP extension defined in this document is 101 generic and is expected to be applicable to other use cases. 103 1.1. Applications Using Port Sets 105 Some applications require not just one port, but a port set. One 106 example is a Session Initiation Protocol (SIP) User Agent Server 107 (UAS) [RFC3261] expecting to handle multiple concurrent calls, 108 including media termination. When it receives a call, it needs to 109 signal media port numbers to its peer. Generating individual PCP MAP 110 requests for each of the media ports during call setup would 111 introduce unwanted latency. Instead, the server can pre-allocate a 112 set of ports such that no PCP exchange is needed during call setup. 114 1.2. Lightweight 4over6 116 In the Lightweight 4over6 (lw4o6) [RFC7596] architecture, shared 117 global addresses can be allocated to customers. It allows moving the 118 Network Address Translation (NAT) function, otherwise accomplished by 119 a Carrier-Grade NAT (CGN) [RFC6888], to the Customer-Premises 120 Equipment (CPE). This provides more control over the NAT function to 121 the user, and more scalability to the ISP. 123 In the lw4o6 architecture, the PCP-controlled device corresponds to 124 the Lightweight AFTR (lwAFTR), and the PCP client corresponds to the 125 Lightweight B4 (lwB4). The PCP client sends a PCP MAP request 126 containing a PORT_SET option to trigger shared address allocation on 127 the Lightweight AFTR (lwAFTR). The PCP response contains the shared 128 address information, including the port set allocated to the 129 Lightweight B4 (lwB4). 131 1.3. Firewall Control 133 Port sets are often used in firewall rules. For example, defining a 134 range for RTP [RFC3550] traffic is common practice. The MAP request 135 can already be used for firewall control. The PORT_SET option brings 136 the additional ability to manipulate firewall rules operating on port 137 sets instead of single ports. 139 1.4. Discovering Stateless Port Set Mappings 141 A MAP request can be used to retrieve a mapping from a stateless 142 device (i.e., one that does not establish any per-flow state, and 143 simply rewrites the address and/or port in a purely algorithmic 144 fashion, including no rewriting). Similarly, a MAP request with a 145 PORT_SET request can be used to discover a port set mapping from a 146 stateless device. See Section 5.2 for an example. 148 2. The need for PORT_SET 150 Multiple MAP requests can be used to manipulate a set of ports, 151 having roughly the same effect as a single use of a MAP request with 152 a PORT_SET option. However, use of the PORT_SET option is more 153 efficient when considering the following aspects: 155 Network Traffic: A single request uses less network resources than 156 multiple requests. 158 Latency: Even though MAP requests can be sent in parallel, we can 159 expect the total processing time to be longer for multiple 160 requests than a single one. 162 Server-side efficiency: Some PCP-controlled devices can allocate 163 port sets in a manner such that data passing through the device is 164 processed much more efficiently than the equivalent using 165 individual port allocations. For example, a CGN having a "bulk" 166 port allocation scheme (see [RFC6888] section 5) often has this 167 property. 169 Server-side scalability: The number of state table entries in PCP- 170 controlled devices is often a limiting factor. Allocating port 171 sets in a single request can result in a single mapping entry 172 being used, therefore allowing greater scalability. 174 Therefore, while it is functionally possible to obtain the same 175 results using plain MAP, the extension proposed in this document 176 allows greater efficiency, scalability, and simplicity, while 177 lowering latency and necessary network traffic. 179 In addition, PORT_SET supports parity preservation. Some protocols 180 (e.g. RTP [RFC3550]) assign meaning to a port number's parity. When 181 mapping sets of ports for the purpose of using such kind of protocol, 182 preserving parity can be necessary. 184 3. Terminology 186 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 187 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 188 document are to be interpreted as described in [RFC2119]. 190 4. The PORT_SET Option 192 Option Name: PORT_SET 194 Number: TBD 196 Purpose: To map sets of ports. 198 Valid for Opcodes: MAP 200 Length: 5 bytes 202 May appear in: Both requests and responses 204 Maximum occurrences: 1 206 The PORT_SET Option indicates that the PCP client wishes to reserve a 207 set of ports. The requested number of ports in that set is indicated 208 in the option. 210 The maximum occurrences of the PORT_SET Option should be limited to 211 1. The reason is that the suggested external port set depends on the 212 data contained in the MAP Opcode header. Having two PORT_SET options 213 with a single MAP Opcode header would imply having two overlapping 214 suggested external port sets. 216 Note that the option number is in the "optional to process" range 217 (128-191), meaning that a MAP request with a PORT_SET option will be 218 interpreted by a PCP server that does not support PORT_SET as a 219 single-port MAP request, as if the PORT_SET option was absent. 221 The PORT_SET Option is formatted as shown in Figure 1. 223 0 1 2 3 224 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 1 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 |Option Code=TBD| Reserved | Option Length=5 | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Port Set Size | First Internal Port | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Reserved |P| 231 +-+-+-+-+-+-+-+-+ 233 Figure 1: PORT_SET Option 235 The fields are as follows: 237 Port Set Size: Number of ports requested. MUST NOT be zero. 239 First Internal Port: In a request, this field MUST be set equal to 240 the Internal Port field in the MAP opcode by the PCP client. In a 241 response, this field indicates the first internal port of the port 242 set mapped by the PCP server, which may differ from the value sent 243 in the request. That is to be contrasted to the Internal Port 244 field, which by necessity is always identical in matched requests 245 and responses. 247 Reserved: MUST be set to zero when sending, MUST be ignored when 248 receiving. 250 P: 1 if parity preservation is requested, 0 otherwise. See 251 [RFC4787], Section 4.2.2. 253 The Internal Port Set is defined as being the range of Port Set Size 254 ports starting from the First Internal Port. The External Port Set 255 is respectively defined as being the range of Port Set Size ports 256 starting from the Assigned External Port. The two ranges always have 257 the same size (i.e., the Port Set Size returned by the PCP server). 259 The Suggested External Port corresponds to the first port in the 260 Assigned External Port Set. Its purpose is for clients to be able to 261 regenerate previous mappings after state loss. When such an event 262 happens, clients may attempt to regenerate identical mappings by 263 suggesting the same External Port Set as before the state loss. Note 264 that there is no guarantee that the allocated External Port Set will 265 be the one suggested by the client. In particular, the 266 PREFER_FAILURE option MUST NOT be present in a request that contains 267 a PORT_SET option. 269 4.1. Client Behavior 271 To retrieve a set of ports, the PCP client adds a PORT_SET option to 272 its PCP MAP request. If port preservation is required, the PCP 273 Client MUST set the parity bit (to 1) to ask the PCP server to 274 preserve the port parity. 276 The PCP Client MUST NOT include more than one PORT_SET option in a 277 MAP request. If several port sets are needed, the PCP client MUST 278 issue separate MAP requests, each potentially including a PORT_SET 279 option. These individual MAP requests MUST include distinct Internal 280 Port. 282 If the PCP Client does not know the exact number of ports it 283 requires, it MAY then set the Port Set Size to 0xffff, indicating 284 that it is willing to accept as many ports as the PCP server can 285 offer. 287 When the PCP-controlled device supports multiple port-sets delegation 288 for a given PCP client, the PCP client MAY re-initiate a PCP request 289 to get another port set when it has exhausted all the ports within 290 the port-set. 292 4.2. Server Behavior 294 In addition to regular MAP request processing, the following checks 295 are made upon receipt of a PORT_SET option with non-zero Requested 296 Lifetime: 298 o If multiple PORT_SET options are present in a single MAP request, 299 a MALFORMED_OPTION error is returned. 301 o If the Port Set Size is zero, a MALFORMED_OPTION error is 302 returned. 304 PREFER_FAILURE MUST NOT appear in a request with PORT_SET option. 305 The PCP server MAY map fewer ports than the value of Port Set Size 306 from the request. It MUST NOT map more ports than the PCP client 307 asked for. Internal ports outside the range of Port Set Size ports 308 starting from the Internal Port MUST NOT be mapped by the PCP server. 310 If the requested port set cannot be fully satisfied, the PCP server 311 SHOULD map as many ports as possible, and SHOULD map at least one 312 port (which is the same behavior as if Port Set Size is set to 1). 314 If the PCP server ends up mapping only a single port, for any reason, 315 the PORT_SET option MUST NOT be present in the response. 317 If the port parity preservation is requested (P = 1), the PCP server 318 MAY preserve port parity. In that case, the External Port is set to 319 a value having the same parity as the First Internal Port. 321 If the mapping is successful, the MAP response's Assigned External 322 Port is set to the first port in the External Port Set, and the 323 PORT_SET option's Port Set Size is set to number of ports in the 324 mapped port set. The First Internal Port field is set to the first 325 port in the Internal Port Set. 327 4.3. Absence of Capability Discovery 329 There is intentionally no port set capability discovery mechanism. A 330 PCP client that wishes to make use of a port set unconditionally 331 includes the PORT_SET option. If no PORT_SET option is present in 332 the response, the PCP client cannot conclude that the PCP server does 333 not support the PORT_SET option. It may just be that the PCP server 334 does support PORT_SET but decided to allocate only a single port, for 335 reasons that are its own. If the client wishes to obtain more ports, 336 it MAY send additional MAP requests (see Section 6.4), which the PCP 337 server may or may not grant according to local policy. 339 If port set capability is added to or removed from a running PCP 340 server, the server MAY reset its Epoch time and send an ANNOUNCE 341 message as described in the PCP specification ([RFC6887], 342 Section 14.1). This causes PCP clients to re-try, and those using 343 PORT_SET will now receive a different response. 345 4.4. Port Set Renewal and Deletion 347 Port set mappings are renewed and deleted as a single entity. That 348 is, the lifetime of all port mappings in the set is set to the 349 Assigned Lifetime at once. 351 A PCP client attempting to refresh or delete a port set mapping MUST 352 include the PORT_SET option in its request. A PCP client MUST NOT 353 send a PORT_SET option for single-port refreshes. 355 4.4.1. Overlap Conditions 357 Port set map requests can overlap with existing single port or port 358 set mappings. This can happen either by mistake or after a PCP 359 client becomes out of sync with server state. 361 If a PCP server receives a MAP request, with or without a PORT_SET 362 option, that tries to map one or more internal ports or port sets 363 belonging to already existing mappings, then the request is 364 considered to be a refresh request applying those mappings. Each of 365 the matching port or port set mappings is processed independently, as 366 if a separate refresh request had been received. The processing is 367 as described in Section 15 of [RFC6887]. The PCP server sends a 368 Mapping Update message for each of the mappings. 370 5. Examples 372 5.1. Simple Request on NAT44 374 An application requires a range of 100 IPv4 UDP ports to be mapped to 375 itself. The application running on the host has created sockets 376 bound to IPv4 UDP ports 50,000 to 50,099 for this purpose. It does 377 not care about which external port numbers are allocated. The PCP 378 client sends a PCP request with the following parameters over IPv4: 380 o MAP opcode 382 Mapping Nonce: 384 Protocol: 17 386 Internal Port: 50,000 388 Suggested External Port: 0 390 Suggested External IP Address: ::ffff:0.0.0.0 392 o PORT_SET Option 394 Port Set Size: 100 396 First Internal Port: 50,000 398 P: 0 400 The PCP server is unable to fulfill the request fully: it is 401 configured by local policy to only allocate 32 ports per user. Since 402 the PREFER_FAILURE option is absent from the request, it decides to 403 map UDP ports 37,056 to 37,087 on external address 192.0.2.3 to 404 internal ports 50,000 to 50,031. After setting up the mapping in the 405 NAT44 device it controls, it replies with the following PCP response: 407 o MAP opcode 409 Mapping Nonce: 411 Protocol: 17 412 Internal Port: 50,000 414 Assigned External Port: 37,056 416 Assigned External IP Address: ::ffff:192.0.2.3 418 o PORT_SET Option 420 Port Set Size: 32 422 First Internal Port: 50,000 424 P: 0 426 Upon receiving this response, the host decides that 32 ports is good 427 enough for its purposes. It closes sockets bound to ports 50,032 to 428 50,099, sets up a refresh timer, and starts using the port range it 429 has just been assigned. 431 5.2. Stateless Mapping Discovery 433 A host wants to discover a stateless NAT44 mapping pointing to it. 434 To do so, it sends the following request over IPv4: 436 o MAP opcode 438 Mapping Nonce: 440 Protocol: 0 442 Internal Port: 1 444 Suggested External Port: 0 446 Suggested External IP Address: ::ffff:0.0.0.0 448 o PORT_SET Option 450 Port Set Size: 65,535 452 First Internal Port: 1 454 P: 0 456 The PCP server sends the following response: 458 o MAP opcode 459 Mapping Nonce: 461 Protocol: 0 463 Internal Port: 1 465 Assigned External Port: 26,624 467 Assigned External IP Address: ::ffff:192.0.2.5 469 o PORT_SET Option 471 Port Set Size: 2048 473 First Internal Port: 26,624 475 P: 0 477 From this response, the host understands that a 2048-port stateless 478 mapping is pointing to itself, starting from port 26,624 on external 479 IP address 192.0.2.5. 481 5.3. Resolving Overlap 483 This example relates to Section 4.4.1. 485 Suppose internal port 100 is mapped to external port 100 and port set 486 101-199 is mapped to external port set 201-299. The PCP server 487 receives a MAP request with Internal Port = 100, External Port = 0, 488 and a PORT_SET option with Port Set Size = 100. The request's 489 Mapping Nonce is equal to those of the existing single port and port 490 set mappings. This request is therefore treated as two refresh 491 requests, the first one applying to the single port mapping and the 492 second one applying to the port set mapping. The PCP server updates 493 both mapping's lifetimes as usual then sends two responses: the first 494 one contains Internal Port = 100, External Port = 100, and no 495 PORT_SET option, while the second one contains Internal Port = 101, 496 External Port = 201, and a PORT_SET option with Port Set Size = 99. 498 6. Operational Considerations 500 6.1. Limits and Quotas 502 It is up to the PCP server to determine the port-set quota, if any, 503 for each PCP client. 505 If the PCP server is configured to allocate multiple port-set 506 allocations for one subscriber, the same Assigned External IP Address 507 SHOULD be assigned to the subscriber in multiple port-set responses. 509 To optimize the number of mapping entries maintained by the PCP 510 server, it is RECOMMENDED to configure the PCP server to assign the 511 maximum allowed port set size in a single response. This policy 512 SHOULD be configurable. 514 6.2. High Availability 516 The failover mechanism in MAP [section 14 in [RFC6887]] can also be 517 applied to port sets. 519 6.3. Idempotence 521 A core, desirable property of the PCP protocol is idempotence. In a 522 nutshell, requests produce the same results whether they are executed 523 once or multiple times. This property is preserved with the PORT_SET 524 attribute, with the following caveat: the order in which the PCP 525 server receives requests with overlapping Internal Port Sets will 526 affect the mappings being created and the responses received. 528 For example suppose these two requests are sent by a PCP client: 530 Request A: Internal Port Set 1-10 532 Request B: Internal Port Set 5-14 534 The PCP server's actions will depend on which request is received 535 first. Suppose that A is received before B: 537 Upon reception of A: Internal ports 1-10 are mapped. A success 538 response containing the following fields is sent: 540 Internal Port: 1 542 First Internal Port: 1 544 Port Set Size: 10 546 Upon reception of B: The request matches mapping A. The request is 547 interpreted as a refresh request for mapping A, and a response 548 containing the following fields is sent: 550 Internal Port: 5 552 First Internal Port: 1 553 Port Set Size: 10 555 If the order of reception is reversed (B before A), the created 556 mapping will be different, and the First Internal Port in both 557 responses would then be 5. 559 To avoid surprises, PCP clients MUST ensure that port set mapping 560 requests do not inadvertently overlap. For example, a host's 561 operating system could include a central PCP client process through 562 which port set mapping requests would be arbitrated. Alternatively, 563 individual PCP clients running on the same host would be required to 564 acquire the internal ports from the operating system (e.g., a call to 565 the bind() function from the BSD API) before trying to map them with 566 PCP. 568 6.4. What should a PCP client do when it receives fewer ports than 569 requested? 571 Suppose a PCP client asks for 16 ports and receives 8. What should 572 it do? Should it consider this a final answer? Should it try a 573 second request, asking for 8 more ports? Should it fall back to 8 574 individual MAP requests? This document leaves the answers to be 575 implementation-specific, but describes issues to be considered when 576 answering them. 578 First, the PCP server has decided to allocate 8 ports for some 579 reason. It may be that allocation sizes have been limited by the PCP 580 server's administrator. It may be that the PCP client has reached a 581 quota. It may be that these 8 ports were the last contiguous ones 582 available. Depending on the reason, asking for more ports may or may 583 not be likely to actually yield more ports. However, the PCP client 584 has no way of knowing. 586 Second, not all PCP clients asking for N ports actually need all N 587 ports to function correctly. For example, a DNS resolver could ask 588 for N ports to be used for source port randomization. If fewer than 589 N ports are received, the DNS resolver will still work correctly, but 590 source port randomization will be slightly less efficient, having 591 fewer bits to play with. In that case, it would not make much sense 592 to ask for more ports. 594 Finally, asking for more ports could be considered abuse. External 595 ports are a resource that is to be shared among multiple PCP clients. 596 A PCP client trying to obtain more than its fair share could trigger 597 countermeasures according to local policy. 599 In conclusion, it is expected that for most applications, asking for 600 more ports would not yield benefits justifying the additional costs. 602 7. Security Considerations 604 The security considerations discussed in [RFC6887] apply to this 605 extension. 607 As described in Section 4.4.1, a single PCP request using the 608 PORT_SET option may result in multiple responses. For this to happen 609 it is necessary that the request contain the nonce associated to 610 multiple mappings on the server. Therefore, an on-path attacker 611 could use an eavesdropped nonce to mount an amplification attack. 612 Use of PCP authentication ([RFC6887], Section 18) eliminates this 613 attack vector. 615 8. IANA Considerations 617 IANA has allocated value TBD (note to IANA: to be allocated from the 618 range 128-191) in the "PCP Options" registry at 619 http://www.iana.org/assignments/pcp-parameters for the new PCP option 620 defined in Section 4. 622 9. Contributors 624 The following are extended authors who contributed to the effort: 626 Yunqing Chen 628 China Telecom 630 Room 502, No.118, Xizhimennei Street 632 Beijing 100035 634 P.R.China 636 Chongfeng Xie 638 China Telecom 640 Room 502, No.118, Xizhimennei Street 642 Beijing 100035 644 P.R.China 646 Yong Cui 648 Tsinghua University 649 Beijing 100084 651 P.R.China 653 Phone: +86-10-62603059 655 Email: yong@csnet1.cs.tsinghua.edu.cn 657 Qi Sun 659 Tsinghua University 661 Beijing 100084 663 P.R.China 665 Phone: +86-10-62785822 667 Email: sunqibupt@gmail.com 669 Gabor Bajko 671 Nokia 673 Email: gabor.bajko@nokia.com 675 Xiaohong Deng 677 France Telecom 679 Email: xiaohong.deng@orange-ftgroup.com 681 10. Acknowledgements 683 The authors would like to show sincere appreciation to Alain Durand, 684 Cong Liu, Dan Wing, Dave Thaler, Peter Koch, Reinaldo Penno, Sam 685 Hartman, Stuart Cheshire, Ted Lemon, and Yoshihiro Ohba, for their 686 useful comments and suggestions. 688 11. References 690 11.1. Normative References 692 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 693 Requirement Levels", BCP 14, RFC 2119, March 1997. 695 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 696 Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 697 2013. 699 11.2. Informative References 701 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 702 A., Peterson, J., Sparks, R., Handley, M., and E. 703 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 704 June 2002. 706 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 707 Jacobson, "RTP: A Transport Protocol for Real-Time 708 Applications", STD 64, RFC 3550, July 2003. 710 [RFC4787] Audet, F. and C. Jennings, "Network Address Translation 711 (NAT) Behavioral Requirements for Unicast UDP", BCP 127, 712 RFC 4787, January 2007. 714 [RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A., 715 and H. Ashida, "Common Requirements for Carrier-Grade NATs 716 (CGNs)", BCP 127, RFC 6888, April 2013. 718 [RFC7596] Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and 719 I. Farrer, "Lightweight 4over6: An Extension to the DS- 720 Lite Architecture", draft-ietf-softwire-lw4over6-03 (work 721 in progress), July 2015. 723 Authors' Addresses 725 Qiong Sun 726 China Telecom 727 P.R.China 729 Phone: 86 10 58552936 730 Email: sunqiong@ctbri.com.cn 732 Mohamed Boucadair 733 France Telecom 734 Rennes 35000 735 France 737 Email: mohamed.boucadair@orange.com 738 Senthil Sivakumar 739 Cisco Systems 740 7100-8 Kit Creek Road 741 Research Triangle Park, North Carolina 27709 742 USA 744 Phone: +1 919 392 5158 745 Email: ssenthil@cisco.com 747 Cathy Zhou 748 Huawei Technologies 749 Bantian, Longgang District 750 Shenzhen 518129 751 P.R. China 753 Email: cathy.zhou@huawei.com 755 Tina Tsou 756 Huawei Technologies (USA) 757 2330 Central Expressway 758 Santa Clara, CA 95050 759 USA 761 Phone: +1 408 330 4424 762 Email: Tina.Tsou.Zouting@huawei.com 764 Simon Perreault 765 Jive Communications 766 Quebec, QC 767 Canada 769 Email: sperreault@jive.com