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Berger, Ed. 5 Expires: September 12, 2019 LabN Consulting, L.L.C. 6 March 11, 2019 8 DLEP Multi-Hop Forwarding Extension 9 draft-ietf-manet-dlep-multi-hop-extension-06 11 Abstract 13 This document defines an extension to the DLEP protocol that enables 14 the reporting and control of Multi-Hop Forwarding by DLEP capable 15 modems. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on September 12, 2019. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Extension Usage and Identification . . . . . . . . . . . . . 3 54 3. Extension Data Items . . . . . . . . . . . . . . . . . . . . 3 55 3.1. Hop Count . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3.2. Hop Control . . . . . . . . . . . . . . . . . . . . . . . 5 57 3.2.1. Reset . . . . . . . . . . . . . . . . . . . . . . . . 6 58 3.2.2. Terminate . . . . . . . . . . . . . . . . . . . . . . 7 59 3.2.3. Direct Connection . . . . . . . . . . . . . . . . . . 7 60 3.2.4. Suppress Forwarding . . . . . . . . . . . . . . . . . 7 61 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 62 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 63 5.1. Extension Type Value . . . . . . . . . . . . . . . . . . 8 64 5.2. Data Item Values . . . . . . . . . . . . . . . . . . . . 8 65 5.3. Hop Control Actions Registry . . . . . . . . . . . . . . 9 66 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 67 6.1. Normative References . . . . . . . . . . . . . . . . . . 9 68 6.2. Informative References . . . . . . . . . . . . . . . . . 10 69 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 10 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 72 1. Introduction 74 The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175]. 75 It provides the exchange of link related control information between 76 DLEP peers. DLEP peers are comprised of a modem and a router. DLEP 77 defines a base set of mechanisms as well as support for possible 78 extensions. This document defines one such extension. 80 Some modem technologies support mobile ad hoc network (MANET) 81 forwarding where connectivity to destinations is provided via 82 forwarding in intermediate modems. This document refers to 83 forwarding by intermediate modems as 'multi-hop forwarding'. example 84 using . DLEP Destination messages can be used to report such 85 reachable destinations, see [RFC8175], but do not provide any 86 information related to the number or capacity of the hops. The 87 extension defined in this document enables modems to inform routers 88 when multi-hop forwarding is being used, and routers to request that 89 modems change multi-hop forwarding behavior. The extension defined 90 in this document is referred to as "Multi-Hop Forwarding", where each 91 modem that transmits/sends data to reach a particular destination is 92 counted as a hop. 94 It is important to note that the use of the hop control mechanism 95 defined in this can result in connectivity changes and even loss of 96 the ability to reach one or more destinations. The defined mechanism 97 will report such connectivity changes, but the details of what a 98 router does or how it reacts to such are out scope of this document. 100 This document defines a new DLEP Extension Type Value in Section 2 101 which is used to indicate the use of the extension, and three new 102 DLEP Data Items in Section 3. 104 1.1. Key Words 106 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 107 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 108 "OPTIONAL" in this document are to be interpreted as described in BCP 109 14 [RFC2119] [RFC8174] when, and only when, they appear in all 110 capitals, as shown here. 112 2. Extension Usage and Identification 114 The use of the Multi-Hop Forwarding Extension SHOULD be configurable. 115 To indicate that the extension is to be used, an implementation MUST 116 include the Multi-Hop Forwarding Extension Type Value in the 117 Extensions Supported Data Item. The Extensions Supported Data Item 118 is sent and processed according to [RFC8175]. 120 The Multi-Hop Forwarding Extension Type Value is TBA1, see Section 5. 122 3. Extension Data Items 124 Three data items are defined by this extension. The Hop Count Data 125 Item is used by a modem to provide the number of modem hops traversed 126 to reach a particular destination. The Hop Control Data Item is used 127 by a router to request that a modem alter connectivity to a 128 particular destination. The Suppress Forwarding Data Item is used by 129 a router to request that a modem disable multi-hop forwarding on 130 either a device or destination basis. 132 3.1. Hop Count 134 The Hop Count Data Item is used by a modem to indicate the number of 135 modem that transmits/sends data to reach a particular destination, 136 i.e., hops, between the modem and a specific destination. In other 137 words, each hop represents a transmission and the number of hops is 138 equal to the number of transmissions required to go from a router 139 connected modem to the destination's connected modem. The minimum 140 number of hops is 1, which represents transmission to destinations 141 that are directly reachable via the router's locally connected modem. 143 The data item also contains an indication of when a destination which 144 currently has a hop count of greater than one (1) could be made 145 directly reachable by a modem, e.g., by re-aiming an antenna. 147 The Hop Count Data Item SHOULD be carried in the Destination Up, 148 Destination Update, Destination Announce Response, and Link 149 Characteristics Response Messages when the Hop Count to a destination 150 is greater than one (1). 152 A router receiving a Hop Count Data Item can use this information in 153 its forwarding and routing decisions, and specific use is out of 154 scope of this document. The absence of the Hop Count Data Item MUST 155 be interpreted by the router as a Hop Count value of one (1). 157 The format of the Hop Count Data Item is: 159 0 1 2 3 160 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 1 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | Data Item Type | Length | 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 |P| Reserved | Hop Count | 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 Data Item Type: TBA2 169 Length: 2 171 P: 173 The P-bit indicates that a destination is potentially directly 174 reachable. When the P-bit is set, the router MAY request a direct 175 link to the associated destination using the Hop Control Data Item 176 described below. This field MUST be ignored when the value 177 contained in the Hop Count field is one (1). 179 Reserved: 181 MUST be set to zero by the sender (a modem) and ignored by the 182 receiver (a router). 184 Hop Count: 186 An unsigned 8-bit integer indicating the number of modem hops 187 required (i.e., number of times a packet will be transmitted) to 188 reach the destination indicated in the message. The special value 189 of 255 (0xFF) is used to indicate that the number of hops is an 190 unknown number greater than one (1). This field MUST contain a 191 value of at least one (1) if the associated destination is 192 reachable. 194 A value of zero (0) is used to indicate that processing of a Hop 195 Control action, see Section 3.2, has resulted in the destination 196 no longer being reachable. A zero value MUST NOT be used in any 197 message other then a Link Characteristics Response Message. 199 3.2. Hop Control 201 The Hop Control Data Item is used by a router to request a change in 202 connectivity to a particular destination, or in multi-hop processing 203 on a device wide basis. A router can request multi-hop reachable 204 destination be changed to a single hop. A router can also indicate 205 that the modem terminates a previous direct connectivity request to a 206 particular destination. 208 The Hop Control Data Item MAY be carried in a Session Update Message 209 sent by a router when the control applies to the whole device, or a 210 Link Characteristics Request Message when the control applies to a 211 particular destination. 213 A modem that receives the Hop Control Data Item in a Link 214 Characteristics Request Message SHOULD take whatever actions are 215 needed to make the change indicated by the data item for the 216 associated destination MAC address. Once the change is made, fails 217 or is rejected, the modem MUST respond with a Link Characteristics 218 Response Message containing an updated Hop Count Data Item. Note 219 that other destinations can be impacted as a result of the change and 220 such changes are reported in Destination Down and Destination Update 221 Messages. The modem MUST notify the router of each destination that 222 is not identified in the Link Characteristics Response Message and is 223 no longer reachable via a Destination Down Message. The modem MUST 224 also notify the router of each destination that is not identified in 225 the Link Characteristics Response Message and has a changed Hop Count 226 impacted via a Destination Update Message. 228 Failures may occur for multiple reasons, for example, the 229 transmission characteristics of the link don't support the one-hop 230 connection at the time of the request. Requests may be rejected by 231 local policy. 233 A modem that receives the Hop Control Data Item in a Session Update 234 Message SHOULD take whatever actions are needed to make the change 235 indicated by the data item for all known destinations. Once the 236 change is made, or fails or is rejected, the modem MUST respond with 237 a Session Update Response Message with an appropriate Status Code. 238 Destination specific impact resulting from the processing of a Hop 239 Control Data Item in a Session Update Message is provided via 240 Destination Down and Destination Update Messages. The modem MUST 241 notify the router of each destination that is no longer reachable via 242 a Destination Down Message. The modem MUST notify the router of any 243 changes in Hop Counts via Destination Update Messages. 245 The format of the Hop Control Data Item is: 247 0 1 2 3 248 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 1 249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 250 | Data Item Type | Length | 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | Hop Control Actions | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 Data Item Type: TBA3 257 Length: 2 259 Hop Control Actions: 261 An unsigned 16-bit value with the following meaning: 263 +-------+---------------------+ 264 | Value | Action | 265 +-------+---------------------+ 266 | 0 | Reset | 267 | | | 268 | 1 | Terminate | 269 | | | 270 | 2 | Direct Connection | 271 | | | 272 | 3 | Suppress Forwarding | 273 +-------+---------------------+ 275 Table 1: Hop Control Actions Values 277 3.2.1. Reset 279 The Reset Action requests that the default behavior be restored. 280 When received in a Session Update Message message, a modem MUST clear 281 all control actions that have previously been processed on a device 282 wide basis, and revert to its configured behavior. When received in 283 a Link Characteristics Request Message, a modem MUST clear all 284 control actions that have previously been processed for the 285 destination indicated in the message. 287 3.2.2. Terminate 289 The Terminate Action is only valid on a per destination basis and 290 MUST NOT be sent in a Session Update Message message. It indicates 291 that a direct connection is no longer needed with the destination 292 identified in the message. This request has no impact for multi-hop 293 destinations and may fail even in a single hop case, i.e. can result 294 in the Hop Count to the destination not being impacted by the 295 processing of the request. 297 3.2.3. Direct Connection 299 The Direct Connection is only valid on a per destination basis and 300 MUST NOT be sent in a Session Update Message message. It indicates 301 that the modem SHOULD attempt to establish a direct connection with 302 the destination identified in the message. This action SHOULD only 303 be sent for destinations for which the Hop Count is greater than 1 304 and has the P-Bit set in the previously received Hop Count Data Item. 305 Results of the request for the destination identified in the message 306 are provided as described above. 308 3.2.4. Suppress Forwarding 310 The Suppress Forwarding Action is used by a router to indicate to its 311 peer that multi-hop forwarding performed by the modem is to be 312 suppressed. A router may request that multi-hop forwarding may be 313 suppressed on a device wide or destination specific basis. 315 A modem which receives the Suppress Forwarding Data Item in a Session 316 Update Message MUST suppress multi-hop forwarding on a device wide 317 basis. This means that data traffic originating from the modem's 318 peer router SHALL only be sent by the modem to destinations that are 319 one modem hop away, and that any data traffic received by the modem 320 from another modem that is not destined to the peer router SHALL be 321 dropped. Impact to destination hop counts are provided to the router 322 by the modem as described above. 324 A modem which receives the Suppress Forwarding Data Item in a Link 325 Characteristics Request Message MUST suppress multi-hop forwarding 326 for only the destination indicated in the message. This means that 327 data traffic originating from the modem's peer router SHALL be sent 328 by the modem to the destination indicated in the Link Characteristics 329 Request Message only when it is one modem hop away. Notably, data 330 traffic received by the modem from another modem can be forwarded by 331 the modem per its normal processing. Results are provided as 332 described above. 334 4. Security Considerations 336 The extension enables the reporting and control of forwarding 337 information by DLEP capable modems. The extension does not 338 inherently introduce any additional threats above those documented in 339 [RFC8175]. The approach taken to Security in that document applies 340 equally when running the extension defined in this document. 342 This extension does define one mechanism that is worth particular 343 note. This extension includes a Hop Control mechanism, see 344 Section 3.2, that is similar to the Link Characteristics Request 345 Message defined in [RFC8175] in that it can impact the set of 346 destinations reported as reachable. With the Link Characteristics 347 Request Message, this risk is implicit. With the Hop Control 348 mechanism defined in this document it is more likely. From a 349 security perspective, implementations should be aware of this 350 increased risk and may choose to implement additional configuration 351 control mechanisms to ensure that the Hop Control mechanism is only 352 used under conditions intended by the network operator. 354 5. IANA Considerations 356 This document requests the assignment of 3 values by IANA. All 357 assignments are to registries defined by [RFC8175]. It also requests 358 creation of one new registry. 360 5.1. Extension Type Value 362 This document requests 1 new assignment to the DLEP Extensions 363 Registry named "Extension Type Values" in the range with the 364 "Specification Required" policy. The requested value is as follows: 366 +------+----------------------+ 367 | Code | Description | 368 +------+----------------------+ 369 | TBA1 | Multi-Hop Forwarding | 370 +------+----------------------+ 372 Table 2: Requested Extension Type Value 374 5.2. Data Item Values 376 This document requests 2 new assignments to the DLEP Data Item 377 Registry named "Data Item Type Values" in the range with the 378 "Specification Required" policy. The requested values are as 379 follows: 381 +-----------+-------------+ 382 | Type Code | Description | 383 +-----------+-------------+ 384 | TBA2 | Hop Count | 385 | | | 386 | TBA3 | Hop Control | 387 +-----------+-------------+ 389 Table 3: Requested Data Item Values 391 5.3. Hop Control Actions Registry 393 Upon approval of this document, IANA is requested to create a new 394 DLEP registry, named "Hop Control Actions Values". The following 395 table provides initial registry values and the [RFC8126] defined 396 policies that should apply to the registry: 398 +-------------+------------------------+ 399 | Value | Action/Policy | 400 +-------------+------------------------+ 401 | 0 | Reset | 402 | | | 403 | 1 | Terminate | 404 | | | 405 | 2 | Direct Connection | 406 | | | 407 | 3 | Suppress Forwarding | 408 | | | 409 | 4-65519 | Specification Required | 410 | | | 411 | 65520-65534 | Private Use | 412 | | | 413 | 65535 | Reserved | 414 +-------------+------------------------+ 416 Table 4: Hop Control Actions Values 418 6. References 420 6.1. Normative References 422 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 423 Requirement Levels", BCP 14, RFC 2119, 424 DOI 10.17487/RFC2119, March 1997, 425 . 427 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 428 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 429 May 2017, . 431 [RFC8175] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B. 432 Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175, 433 DOI 10.17487/RFC8175, June 2017, 434 . 436 6.2. Informative References 438 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 439 Writing an IANA Considerations Section in RFCs", BCP 26, 440 RFC 8126, DOI 10.17487/RFC8126, June 2017, 441 . 443 Appendix A. Acknowledgments 445 Helpful comments were received from members of the MANET working 446 grouping, including Henning Rogge, Victoria Pritchard and David 447 Wiggins. 449 Authors' Addresses 451 Bow-Nan Cheng 452 MIT Lincoln Laboratory 453 Massachusetts Institute of Technology 454 244 Wood Street 455 Lexington, MA 02421-6426 457 Email: bcheng@ll.mit.edu 459 Lou Berger (editor) 460 LabN Consulting, L.L.C. 462 Email: lberger@labn.net