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Miscellaneous warnings: ---------------------------------------------------------------------------- == Line 708 has weird spacing: '... ar$sha noct...' == Line 709 has weird spacing: '... ar$spa moct...' == Line 710 has weird spacing: '... ar$tha noct...' == Line 711 has weird spacing: '... ar$tpa moct...' == Line 813 has weird spacing: '... ar$sha unk...' == (16 more instances...) == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (September 10, 1998) is 9332 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: '5' is defined on line 1382, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. '1' -- Possible downref: Non-RFC (?) normative reference: ref. '2' -- Possible downref: Non-RFC (?) normative reference: ref. '3' ** Obsolete normative reference: RFC 1638 (ref. '4') (Obsoleted by RFC 2878) -- Possible downref: Non-RFC (?) normative reference: ref. '5' ** Obsolete normative reference: RFC 1700 (ref. '7') (Obsoleted by RFC 3232) -- Possible downref: Non-RFC (?) normative reference: ref. '10' ** Obsolete normative reference: RFC 1293 (ref. '11') (Obsoleted by RFC 2390) -- Possible downref: Non-RFC (?) normative reference: ref. '12' -- Possible downref: Non-RFC (?) normative reference: ref. '13' -- Possible downref: Non-RFC (?) normative reference: ref. '14' -- Possible downref: Non-RFC (?) normative reference: ref. '15' -- Possible downref: Non-RFC (?) normative reference: ref. '18' Summary: 14 errors (**), 0 flaws (~~), 9 warnings (==), 14 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Brown 3 INTERNET DRAFT Fore Systems, Inc. 4 Obsoletes: 1294, 1490 A. Malis 5 Ascend Communications, Inc. 6 March 11, 1998 7 Expires September 10, 1998 9 Multiprotocol Interconnect over Frame Relay 11 Status of this Memo 13 This document is an Internet-Draft. Internet-Drafts are working 14 documents of the Internet Engineering Task Force (IETF), its areas, 15 and its working groups. Note that other groups may also distribute 16 working documents as Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as ``work in progress.'' 23 To learn the current status of any Internet-Draft, please check the 24 ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow 25 Directories on ds.internic.net (US East Coast), nic.nordu.net 26 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 27 Rim). 29 This draft specifies an IAB standards track protocol for the Internet 30 community, and requests discussion and suggestions for improvements. 31 Please refer to the current edition of the "IAB Official Protocol 32 Standards" for the standardization state and status of this protocol. 33 Distribution of this memo is unlimited. 35 Abstract 37 This memo describes an encapsulation method for carrying network 38 interconnect traffic over a Frame Relay backbone. It covers aspects 39 of both Bridging and Routing. 41 Systems with the ability to transfer both the encapsulation method 42 described in this document, and others must have a priori knowledge 43 of which virtual circuits will carry which encapsulation method and 44 this encapsulation must only be used over virtual circuits that have 45 been explicitly configured for its use. 47 Acknowledgments 49 This document could not have been completed without the support of 50 Terry Bradley of Avici Systems, Inc.. Comments and contributions 51 from many sources, especially those from Ray Samora of Proteon, Ken 52 Rehbehn of Visual Networks, Fred Baker and Charles Carvalho of Cisco 53 Systems, and Mostafa Sherif of AT&T have been incorporated into this 54 document. Special thanks to Dory Leifer of University of Michigan for 55 his contributions to the resolution of fragmentation issues (though 56 it was deleted in the final version) and Floyd Backes and Laura 57 Bridge of 3Com for their contributions to the bridging descriptions. 58 This document could not have been completed without the expertise of 59 the IP over Large Public Data Networks and the IP over NBMA working 60 groups of the IETF. 62 Modifications from RFC 1490 64 RFC 1490 has been widely implemented and used, and has been adopted 65 by the Frame Relay Forum in FRF.3.1 [15] and by the ITU in Q.933 [2]. 66 This section describes updates to RFC 1490 that have been made as a 67 result of this implementation and interoperability experience, and 68 which reflect current implementation practice. 70 Some language changes were necessary to clarify RFC 1490. None of 71 these changes impacted the technical aspects of this document, but 72 were required to keep diagrams and language specific and consistent. 73 Specifics of these changes will not be listed here. Below are listed 74 those changes which were significant. 76 a) The requirement for stations to accept SNAP encapsulated protocols 77 for which a NLPID was available, was removed. RFC 1490 indicated 78 that, if a protocol, such as IP, had a designated NLPID value, it 79 must be used. Later the document required stations to accept a 80 SNAP encapsulated version of this same protocol. This is clearly 81 inconsistent. A compliant station must send and accept the NLPID 82 encapsulated version of such a protocol. It MAY accept the SNAP 83 encapsulation but should not be required to do so as these frames 84 are noncompliant. 86 b) Fragmentation was removed. To date there are no interoperable 87 implementations of the fragmentation algorithm presented in RFC 88 1490. Additionally, there have been several suggestions that the 89 proposed mechanisms are insufficient for some frame relay 90 applications. To this end, fragmentation was removed from this 91 document, and has been replaced by the fragmentation specified in 92 FRF.12 [18]. 94 c) The address resolution presented in RFC 1490 referred only to 95 PVC environments and is insufficient for SVC environments. 96 Therefore the section title was changed to reflect this. Further 97 work on SVC address resolution will take place in the ION working 98 group. 100 d) The encapsulation for Source Routing BPDUs was added, and the 101 lists in Appendix A were augmented. 103 e) The use of canonical and non-canonical MAC destination addresses 104 in the bridging encapsulations was clarified. 106 f) Explicit support for multiple IP addresses mapped to a single 107 Frame Relay DLCI. 109 g) A new security section was added. 111 1. Conventions and Acronyms 113 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 114 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 115 document, are to be interpreted as described in [16]. 117 All drawings in this document are drawn with the left-most bit as the 118 high order bit for transmission. For example, the drawings might be 119 labeled as: 121 0 1 2 3 4 5 6 7 bits 122 +---+---+---+---+---+---+---+ 124 +---------------------------+ 125 | flag (7E hexadecimal) | 126 +---------------------------+ 127 | Q.922 Address* | 128 +-- --+ 129 | | 130 +---------------------------+ 131 : : 132 : : 133 +---------------------------+ 135 Drawings that would be too large to fit onto one page if each octet 136 were presented on a single line are drawn with two octets per line. 137 These are also drawn with the left-most bit as the high order bit for 138 transmission. There will be a "+" to distinguish between octets as 139 in the following example. 141 |--- octet one ---|--- octet two ---| 142 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 143 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 145 +--------------------------------------------+ 146 | Organizationally Unique | 147 +-- +--------------------+ 148 | Identifier | Protocol | 149 +-----------------------+--------------------+ 150 | Identifier | 151 +-----------------------+ 153 The following are common acronyms used throughout this document. 155 BECN - Backward Explicit Congestion Notification 156 BPDU - Bridge Protocol Data Unit 157 C/R - Command/Response bit 158 DCE - Data Communication Equipment 159 DE - Discard Eligibility bit 160 DTE - Data Terminal Equipment 161 FECN - Forward Explicit Congestion Notification 162 PDU - Protocol Data Unit 163 PTT - Postal Telephone & Telegraph 164 SNAP - Subnetwork Access Protocol 166 2. Introduction 168 The following discussion applies to those devices which serve as end 169 stations (DTEs) on a public or private Frame Relay network (for 170 example, provided by a common carrier or PTT. It will not discuss 171 the behavior of those stations that are considered a part of the 172 Frame Relay network (DCEs) other than to explain situations in which 173 the DTE must react. 175 The Frame Relay network provides a number of virtual circuits that 176 form the basis for connections between stations attached to the same 177 Frame Relay network. The resulting set of interconnected devices 178 forms a private Frame Relay group which may be either fully 179 interconnected with a complete "mesh" of virtual circuits, or only 180 partially interconnected. In either case, each virtual circuit is 181 uniquely identified at each Frame Relay interface by a Data Link 182 Connection Identifier (DLCI). In most circumstances, DLCIs have 183 strictly local significance at each Frame Relay interface. 185 The specifications in this document are intended to apply to both 186 switched and permanent virtual circuits. 188 3. Frame Format 190 All protocols must encapsulate their packets within a Q.922 Annex A 191 frame [1]. Additionally, frames shall contain information necessary 192 to identify the protocol carried within the protocol data unit (PDU), 193 thus allowing the receiver to properly process the incoming packet. 194 The format shall be as follows: 196 +---------------------------+ 197 | flag (7E hexadecimal) | 198 +---------------------------+ 199 | Q.922 Address* | 200 +-- --+ 201 | | 202 +---------------------------+ 203 | Control (UI = 0x03) | 204 +---------------------------+ 205 | Pad (when required) (0x00)| 206 +---------------------------+ 207 | NLPID | 208 +---------------------------+ 209 | . | 210 | . | 211 | . | 212 | Data | 213 | . | 214 | . | 215 +---------------------------+ 216 | Frame Check Sequence | 217 +-- . --+ 218 | (two octets) | 219 +---------------------------+ 220 | flag (7E hexadecimal) | 221 +---------------------------+ 223 * Q.922 addresses, as presently defined, are two octets and 224 contain a 10-bit DLCI. In some networks Q.922 addresses 225 may optionally be increased to three or four octets. 227 The control field is the Q.922 control field. The UI (0x03) value is 228 used unless it is negotiated otherwise. The use of XID (0xAF or 229 0xBF) is permitted and is discussed later. 231 The pad field is used to align the data portion (beyond the 232 encapsulation header) of the frame to a two octet boundary. If 233 present, the pad is a single octet and must have a value of zero. 234 Explicit directions of when to use the pad field are discussed later 235 in this document. 237 The Network Level Protocol ID (NLPID) field is administered by ISO 238 and the ITU. It contains values for many different protocols 239 including IP, CLNP, and IEEE Subnetwork Access Protocol (SNAP)[10]. 240 This field tells the receiver what encapsulation or what protocol 241 follows. Values for this field are defined in ISO/IEC TR 9577 [3]. A 242 NLPID value of 0x00 is defined within ISO/IEC TR 9577 as the Null 243 Network Layer or Inactive Set. Since it cannot be distinguished from 244 a pad field, and because it has no significance within the context of 245 this encapsulation scheme, a NLPID value of 0x00 is invalid under the 246 Frame Relay encapsulation. Appendix A contains a list of some of the 247 more commonly used NLPID values. 249 There is no commonly implemented minimum maximum frame size for Frame 250 Relay. A network must, however, support at least a 262 octet 251 maximum. Generally, the maximum will be greater than or equal to 252 1600 octets, but each Frame Relay provider will specify an 253 appropriate value for its network. A Frame Relay DTE, therefore, 254 must allow the maximum acceptable frame size to be configurable. 256 The minimum frame size allowed for Frame Relay is five octets between 257 the opening and closing flags assuming a two octet Q.922 address 258 field. This minimum increases to six octets for three octet Q.922 259 address and seven octets for the four octet Q.922 address format. 261 4. Interconnect Issues 263 There are two basic types of data packets that travel within the 264 Frame Relay network: routed packets and bridged packets. These 265 packets have distinct formats and therefore, must contain an 266 indicator that the destination may use to correctly interpret the 267 contents of the frame. This indicator is embedded within the NLPID 268 and SNAP header information. 270 For those protocols that do not have a NLPID already assigned, it is 271 necessary to provide a mechanism to allow easy protocol 272 identification. There is a NLPID value defined indicating the 273 presence of a SNAP header. 275 A SNAP header is of the form: 277 +--------------------------------------------+ 278 | Organizationally Unique | 279 +-- +--------------------+ 280 | Identifier | Protocol | 281 +-----------------------+--------------------+ 282 | Identifier | 283 +-----------------------+ 285 The three-octet Organizationally Unique Identifier (OUI) identifies 286 an organization which administers the meaning of the Protocol 287 Identifier (PID) which follows. Together they identify a distinct 288 protocol. Note that OUI 0x00-00-00 specifies that the following PID 289 is an Ethertype. 291 4.1. Routed Frames 293 Some protocols will have an assigned NLPID, but because the NLPID 294 numbering space is limited, not all protocols have specific NLPID 295 values assigned to them. When packets of such protocols are routed 296 over Frame Relay networks, they are sent using the NLPID 0x80 (which 297 indicates the presence of a SNAP header) followed by SNAP. If the 298 protocol has an Ethertype assigned, the OUI is 0x00-00-00 (which 299 indicates an Ethertype follows), and PID is the Ethertype of the 300 protocol in use. 302 When a SNAP header is present as described above, a one octet pad is 303 used to align the protocol data on a two octet boundary as shown 304 below. 306 Format of Routed Frames 307 with a SNAP Header 308 +-------------------------------+ 309 | Q.922 Address | 310 +---------------+---------------+ 311 | Control 0x03 | pad 0x00 | 312 +---------------+---------------+ 313 | NLPID 0x80 | Organization- | 314 +---------------+ | 315 | ally Unique Identifier (OUI) | 316 +-------------------------------+ 317 | Protocol Identifier (PID) | 318 +-------------------------------+ 319 | | 320 | Protocol Data | 321 | | 322 +-------------------------------+ 323 | FCS | 324 +-------------------------------+ 326 In the few cases when a protocol has an assigned NLPID (see Appendix 327 A), 48 bits can be saved using the format below: 329 Format of Routed NLPID Protocol 330 +-------------------------------+ 331 | Q.922 Address | 332 +---------------+---------------+ 333 | Control 0x03 | NLPID | 334 +---------------+---------------+ 335 | Protocol Data | 336 +-------------------------------+ 337 | FCS | 338 +-------------------------------+ 340 When using the NLPID encapsulation format as described above, the pad 341 octet is not used. 343 In the case of ISO protocols, the NLPID is considered to be the first 344 octet of the protocol data. It is unnecessary to repeat the NLPID in 345 this case. The single octet serves both as the demultiplexing value 346 and as part of the protocol data (refer to "Other Protocols over 347 Frame Relay for more details). Other protocols, such as IP, have a 348 NLPID defined (0xCC), but it is not part of the protocol itself. 350 Format of Routed IP Datagram 351 +-------------------------------+ 352 | Q.922 Address | 353 +---------------+---------------+ 354 | Control 0x03 | NLPID 0xCC | 355 +---------------+---------------+ 356 | IP Datagram | 357 +-------------------------------+ 358 | FCS | 359 +-------------------------------+ 361 4.2. Bridged Frames 363 The second type of Frame Relay traffic is bridged packets. These 364 packets are encapsulated using the NLPID value of 0x80 indicating 365 SNAP. As with other SNAP encapsulated protocols, there will be one 366 pad octet to align the data portion of the encapsulated frame. The 367 SNAP header which follows the NLPID identifies the format of the 368 bridged packet. The OUI value used for this encapsulation is the 369 802.1 organization code 0x00-80-C2. The PID portion of the SNAP 370 header (the two bytes immediately following the OUI) specifies the 371 form of the MAC header, which immediately follows the SNAP header. 372 Additionally, the PID indicates whether the original FCS is preserved 373 within the bridged frame. 375 Following the precedent in RFC 1638 [4], non-canonical MAC destination 376 addresses are used for encapsulated IEEE 802.5 and FDDI frames, and 377 canonical MAC destination addresses are used for the remaining 378 encapsulations defined in this section. 380 The 802.1 organization has reserved the following values to be used 381 with Frame Relay: 383 PID Values for OUI 0x00-80-C2 385 with preserved FCS w/o preserved FCS Media 386 ------------------ ----------------- ---------------- 387 0x00-01 0x00-07 802.3/Ethernet 388 0x00-02 0x00-08 802.4 389 0x00-03 0x00-09 802.5 390 0x00-04 0x00-0A FDDI 391 0x00-0B 802.6 393 In addition, the PID value 0x00-0E, when used with OUI 0x00-80-C2, 394 identifies Bridge Protocol Data Units (BPDUs) as defined by 395 802.1(d) or 802.1(g) [12], and the PID value 0x00-0F identifies 396 Source Routing BPDUs. 398 A packet bridged over Frame Relay will, therefore, have one of the 399 following formats: 401 Format of Bridged Ethernet/802.3 Frame 402 +-------------------------------+ 403 | Q.922 Address | 404 +---------------+---------------+ 405 | Control 0x03 | pad 0x00 | 406 +---------------+---------------+ 407 | NLPID 0x80 | OUI 0x00 | 408 +---------------+ --+ 409 | OUI 0x80-C2 | 410 +-------------------------------+ 411 | PID 0x00-01 or 0x00-07 | 412 +-------------------------------+ 413 | MAC destination address | 414 : : 415 | | 416 +-------------------------------+ 417 | (remainder of MAC frame) | 418 +-------------------------------+ 419 | LAN FCS (if PID is 0x00-01) | 420 +-------------------------------+ 421 | FCS | 422 +-------------------------------+ 423 Format of Bridged 802.4 Frame 424 +-------------------------------+ 425 | Q.922 Address | 426 +---------------+---------------+ 427 | Control 0x03 | pad 0x00 | 428 +---------------+---------------+ 429 | NLPID 0x80 | OUI 0x00 | 430 +---------------+ --+ 431 | OUI 0x80-C2 | 432 +-------------------------------+ 433 | PID 0x00-02 or 0x00-08 | 434 +---------------+---------------+ 435 | pad 0x00 | Frame Control | 436 +---------------+---------------+ 437 | MAC destination address | 438 : : 439 | | 440 +-------------------------------+ 441 | (remainder of MAC frame) | 442 +-------------------------------+ 443 | LAN FCS (if PID is 0x00-02) | 444 +-------------------------------+ 445 | FCS | 446 +-------------------------------+ 447 Format of Bridged 802.5 Frame 448 +-------------------------------+ 449 | Q.922 Address | 450 +---------------+---------------+ 451 | Control 0x03 | pad 0x00 | 452 +---------------+---------------+ 453 | NLPID 0x80 | OUI 0x00 | 454 +---------------+ --+ 455 | OUI 0x80-C2 | 456 +-------------------------------+ 457 | PID 0x00-03 or 0x00-09 | 458 +---------------+---------------+ 459 | pad 0x00 | Frame Control | 460 +---------------+---------------+ 461 | MAC destination address | 462 : : 463 | | 464 +-------------------------------+ 465 | (remainder of MAC frame) | 466 +-------------------------------+ 467 | LAN FCS (if PID is 0x00-03) | 468 | | 469 +-------------------------------+ 470 | FCS | 471 +-------------------------------+ 472 Format of Bridged FDDI Frame 473 +-------------------------------+ 474 | Q.922 Address | 475 +---------------+---------------+ 476 | Control 0x03 | pad 0x00 | 477 +---------------+---------------+ 478 | NLPID 0x80 | OUI 0x00 | 479 +---------------+ --+ 480 | OUI 0x80-C2 | 481 +-------------------------------+ 482 | PID 0x00-04 or 0x00-0A | 483 +---------------+---------------+ 484 | pad 0x00 | Frame Control | 485 +---------------+---------------+ 486 | MAC destination address | 487 : : 488 | | 489 +-------------------------------+ 490 | (remainder of MAC frame) | 491 +-------------------------------+ 492 | LAN FCS (if PID is 0x00-04) | 493 | | 494 +-------------------------------+ 495 | FCS | 496 +-------------------------------+ 497 Format of Bridged 802.6 Frame 498 +-------------------------------+ 499 | Q.922 Address | 500 +---------------+---------------+ 501 | Control 0x03 | pad 0x00 | 502 +---------------+---------------+ 503 | NLPID 0x80 | OUI 0x00 | 504 +---------------+ --+ 505 | OUI 0x80-C2 | 506 +-------------------------------+ 507 | PID 0x00-0B | 508 +---------------+---------------+ ------- 509 | Reserved | BEtag | Common 510 +---------------+---------------+ PDU 511 | BAsize | Header 512 +-------------------------------+ ------- 513 | MAC destination address | 514 : : 515 | | 516 +-------------------------------+ 517 | (remainder of MAC frame) | 518 +-------------------------------+ 519 | | 520 +- Common PDU Trailer -+ 521 | | 522 +-------------------------------+ 523 | FCS | 524 +-------------------------------+ 526 Note that in bridge 802.6 PDUs, there is only one choice for the PID 527 value, since the presence of a CRC-32 is indicated by the CIB bit in 528 the header of the MAC frame. 530 The Common Protocol Data Unit (CPDU) Header and Trailer are conveyed 531 to allow pipelining at the egress bridge to an 802.6 subnetwork. 532 Specifically, the CPDU Header contains the BAsize field, which 533 contains the length of the PDU. If this field is not available to 534 the egress 802.6 bridge, then that bridge cannot begin to transmit 535 the segmented PDU until it has received the entire PDU, calculated 536 the length, and inserted the length into the BAsize field. If the 537 field is available, the egress 802.6 bridge can extract the length 538 from the BAsize field of the Common PDU Header, insert it into the 539 corresponding field of the first segment, and immediately transmit 540 the segment onto the 802.6 subnetwork. Thus, the bridge can begin 541 transmitting the 802.6 PDU before it has received the complete PDU. 543 One should note that the Common PDU Header and Trailer of the 544 encapsulated frame should not be simply copied to the outgoing 802.6 545 subnetwork because the encapsulated BEtag value may conflict with the 546 previous BEtag value transmitted by that bridge. 548 Format of BPDU Frame 549 +-------------------------------+ 550 | Q.922 Address | 551 +-------------------------------+ 552 | Control 0x03 | 553 +-------------------------------+ 554 | PAD 0x00 | 555 +-------------------------------+ 556 | NLPID 0x80 | 557 +-------------------------------+ 558 | OUI 0x00-80-C2 | 559 +-------------------------------+ 560 | PID 0x00-0E | 561 +-------------------------------+ 562 | | 563 | BPDU as defined by | 564 | 802.1(d) or 802.1(g)[12] | 565 | | 566 +-------------------------------+ 567 | FCS | 568 +-------------------------------+ 570 Format of Source Routing BPDU Frame 571 +-------------------------------+ 572 | Q.922 Address | 573 +-------------------------------+ 574 | Control 0x03 | 575 +-------------------------------+ 576 | PAD 0x00 | 577 +-------------------------------+ 578 | NLPID 0x80 | 579 +-------------------------------+ 580 | OUI 0x00-80-C2 | 581 +-------------------------------+ 582 | PID 0x00-0F | 583 +-------------------------------+ 584 | | 585 | Source Routing BPDU | 586 | | 587 | | 588 +-------------------------------+ 589 | FCS | 590 +-------------------------------+ 592 5. Data Link Layer Parameter Negotiation 594 Frame Relay stations may choose to support the Exchange 595 Identification (XID) specified in Appendix III of Q.922 [1]. This 596 XID exchange allows the following parameters to be negotiated at the 597 initialization of a Frame Relay circuit: maximum frame size N201, 598 retransmission timer T200, and the maximum number of outstanding 599 Information (I) frames K. 601 A station may indicate its unwillingness to support acknowledged mode 602 multiple frame operation by specifying a value of zero for the 603 maximum window size, K. 605 If this exchange is not used, these values must be statically 606 configured by mutual agreement of Data Link Connection (DLC) 607 endpoints, or must be defaulted to the values specified in Section 608 5.9 of Q.922: 610 N201: 260 octets 612 K: 3 for a 16 Kbps link, 613 7 for a 64 Kbps link, 614 32 for a 384 Kbps link, 615 40 for a 1.536 Mbps or above link 617 T200: 1.5 seconds [see Q.922 for further details] 619 If a station supporting XID receives an XID frame, it shall respond 620 with an XID response. In processing an XID, if the remote maximum 621 frame size is smaller than the local maximum, the local system shall 622 reduce the maximum size it uses over this DLC to the remotely 623 specified value. Note that this shall be done before generating a 624 response XID. 626 The following diagram describes the use of XID to specify non-use of 627 acknowledged mode multiple frame operation. 629 Non-use of Acknowledged Mode Multiple Frame Operation 630 +---------------+ 631 | Address | (2,3 or 4 octets) 632 | | 633 +---------------+ 634 | Control 0xAF | 635 +---------------+ 636 | format 0x82 | 637 +---------------+ 638 | Group ID 0x80 | 639 +---------------+ 640 | Group Length | (2 octets) 641 | 0x00-0E | 642 +---------------+ 643 | 0x05 | PI = Frame Size (transmit) 644 +---------------+ 645 | 0x02 | PL = 2 646 +---------------+ 647 | Maximum | (2 octets) 648 | Frame Size | 649 +---------------+ 650 | 0x06 | PI = Frame Size (receive) 651 +---------------+ 652 | 0x02 | PL = 2 653 +---------------+ 654 | Maximum | (2 octets) 655 | Frame Size | 656 +---------------+ 657 | 0x07 | PI = Window Size 658 +---------------+ 659 | 0x01 | PL = 1 660 +---------------+ 661 | 0x00 | 662 +---------------+ 663 | 0x09 | PI = Retransmission Timer 664 +---------------+ 665 | 0x01 | PL = 1 666 +---------------+ 667 | 0x00 | 668 +---------------+ 669 | FCS | (2 octets) 670 | | 671 +---------------+ 673 6. Address Resolution for PVCs 675 This document only describes address resolution as it applies to PVCs. 676 SVC operation will be discussed in future documents. 678 There are situations in which a Frame Relay station may wish to 679 dynamically resolve a protocol address over PVCs. This may be 680 accomplished using the standard Address Resolution Protocol (ARP) [6] 681 encapsulated within a SNAP encoded Frame Relay packet as follows: 683 +-----------------------+-----------------------+ 684 | Q.922 Address | 685 +-----------------------+-----------------------+ 686 | Control (UI) 0x03 | pad 0x00 | 687 +-----------------------+-----------------------+ 688 | NLPID 0x80 | | SNAP Header 689 +-----------------------+ OUI 0x00-00-00 + Indicating 690 | | ARP 691 +-----------------------+-----------------------+ 692 | PID 0x0806 | 693 +-----------------------+-----------------------+ 694 | ARP packet | 695 | . | 696 | . | 697 | . | 698 +-----------------------+-----------------------+ 700 Where the ARP packet has the following format and values: 702 Data: 703 ar$hrd 16 bits Hardware type 704 ar$pro 16 bits Protocol type 705 ar$hln 8 bits Octet length of hardware address (n) 706 ar$pln 8 bits Octet length of protocol address (m) 707 ar$op 16 bits Operation code (request or reply) 708 ar$sha noctets source hardware address 709 ar$spa moctets source protocol address 710 ar$tha noctets target hardware address 711 ar$tpa moctets target protocol address 713 ar$hrd - assigned to Frame Relay is 15 decimal 714 (0x000F) [7]. 716 ar$pro - see assigned numbers for protocol ID number for 717 the protocol using ARP. (IP is 0x0800). 719 ar$hln - length in bytes of the address field (2, 3, or 4) 721 ar$pln - protocol address length is dependent on the 722 protocol (ar$pro) (for IP ar$pln is 4). 724 ar$op - 1 for request and 2 for reply. 726 ar$sha - Q.922 source hardware address, with C/R, FECN, 727 BECN, and DE set to zero. 729 ar$tha - Q.922 target hardware address, with C/R, FECN, 730 BECN, and DE set to zero. 732 Because DLCIs within most Frame Relay networks have only local 733 significance, an end station will not have a specific DLCI assigned 734 to itself. Therefore, such a station does not have an address to put 735 into the ARP request or reply. Fortunately, the Frame Relay network 736 does provide a method for obtaining the correct DLCIs. The solution 737 proposed for the locally addressed Frame Relay network below will 738 work equally well for a network where DLCIs have global significance. 740 The DLCI carried within the Frame Relay header is modified as it 741 traverses the network. When the packet arrives at its destination, 742 the DLCI has been set to the value that, from the standpoint of the 743 receiving station, corresponds to the sending station. For example, 744 in figure 1 below, if station A were to send a message to station B, 745 it would place DLCI 50 in the Frame Relay header. When station B 746 received this message, however, the DLCI would have been modified by 747 the network and would appear to B as DLCI 70. 749 ~~~~~~~~~~~~~~~ 750 ( ) 751 +-----+ ( ) +-----+ 752 | |-50------(--------------------)---------70-| | 753 | A | ( ) | B | 754 | |-60-----(---------+ ) | | 755 +-----+ ( | ) +-----+ 756 ( | ) 757 ( | ) <---Frame Relay 758 ~~~~~~~~~~~~~~~~ network 759 80 760 | 761 +-----+ 762 | | 763 | C | 764 | | 765 +-----+ 766 Figure 1 768 Lines between stations represent data link connections (DLCs). 769 The numbers indicate the local DLCI associated with each 770 connection. 772 DLCI to Q.922 Address Table for Figure 1 774 DLCI (decimal) Q.922 address (hex) 775 50 0x0C21 776 60 0x0CC1 777 70 0x1061 778 80 0x1401 780 For authoritative description of the correlation between DLCI and 781 Q.922 [1] addresses, the reader should consult Q.922. A summary 782 of the correlation is included here for convenience. The 783 translation between DLCI and Q.922 address is based on a two byte 784 address length using the Q.922 encoding format. The format is: 786 8 7 6 5 4 3 2 1 787 +------------------------+---+--+ 788 | DLCI (high order) |c/r|ea| 789 +--------------+----+----+---+--+ 790 | DLCI (lower) |FECN|BECN|DE |EA| 791 +--------------+----+----+---+--+ 793 For ARP and its variants, the FECN, BECN, C/R and DE bits are 794 assumed to be 0. 796 When an ARP message reaches a destination, all hardware addresses 797 will be invalid. The address found in the frame header will, 798 however, be correct. Though it does violate the purity of layering, 799 Frame Relay may use the address in the header as the sender hardware 800 address. It should also be noted that the target hardware address, 801 in both ARP request and reply, will also be invalid. This should not 802 cause problems since ARP does not rely on these fields and in fact, 803 an implementation may zero fill or ignore the target hardware address 804 field entirely. 806 As an example of how this address replacement scheme may work, refer 807 to figure 1. If station A (protocol address pA) wished to resolve 808 the address of station B (protocol address pB), it would format an 809 ARP request with the following values: 811 ARP request from A 812 ar$op 1 (request) 813 ar$sha unknown 814 ar$spa pA 815 ar$tha undefined 816 ar$tpa pB 818 Because station A will not have a source address associated with it, 819 the source hardware address field is not valid. Therefore, when the 820 ARP packet is received, it must extract the correct address from the 821 Frame Relay header and place it in the source hardware address field. 822 This way, the ARP request from A will become: 824 ARP request from A as modified by B 825 ar$op 1 (request) 826 ar$sha 0x1061 (DLCI 70) from Frame Relay header 827 ar$spa pA 828 ar$tha undefined 829 ar$tpa pB 831 Station B's ARP will then be able to store station A's protocol 832 address and Q.922 address association correctly. Next, station B 833 will form a reply message. Many implementations simply place the 834 source addresses from the ARP request into the target addresses and 835 then fills in the source addresses with its addresses. In this case, 836 the ARP response would be: 838 ARP response from B 839 ar$op 2 (response) 840 ar$sha unknown 841 ar$spa pB 842 ar$tha 0x1061 (DLCI 70) 843 ar$tpa pA 845 Again, the source hardware address is unknown and when the request is 846 received, station A will extract the address from the Frame Relay 847 header and place it in the source hardware address field. Therefore, 848 the response will become: 850 ARP response from B as modified by A 851 ar$op 2 (response) 852 ar$sha 0x0C21 (DLCI 50) 853 ar$spa pB 854 ar$tha 0x1061 (DLCI 70) 855 ar$tpa pA 857 Station A will now correctly recognize station B having protocol 858 address pB associated with Q.922 address 0x0C21 (DLCI 50). 860 Reverse ARP (RARP) [8] will work in exactly the same way. Still 861 using figure 1, if we assume station C is an address server, the 862 following RARP exchanges will occur: 864 RARP request from A RARP request as modified by C 865 ar$op 3 (RARP request) ar$op 3 (RARP request) 866 ar$sha unknown ar$sha 0x1401 (DLCI 80) 867 ar$spa undefined ar$spa undefined 868 ar$tha 0x0CC1 (DLCI 60) ar$tha 0x0CC1 (DLCI 60) 869 ar$tpa pC ar$tpa pC 871 Station C will then look up the protocol address corresponding to 872 Q.922 address 0x1401 (DLCI 80) and send the RARP response. 874 RARP response from C RARP response as modified by A 875 ar$op 4 (RARP response) ar$op 4 (RARP response) 876 ar$sha unknown ar$sha 0x0CC1 (DLCI 60) 877 ar$spa pC ar$spa pC 878 ar$tha 0x1401 (DLCI 80) ar$tha 0x1401 (DLCI 80) 879 ar$tpa pA ar$tpa pA 881 This means that the Frame Relay interface must only intervene in the 882 processing of incoming packets. 884 In the absence of suitable multicast, ARP may still be implemented. 885 To do this, the end station simply sends a copy of the ARP request 886 through each relevant DLC, thereby simulating a broadcast. 888 The use of multicast addresses in a Frame Relay environment is 889 presently under study by Frame Relay providers. At such time that 890 the issues surrounding multicasting are resolved, multicast 891 addressing may become useful in sending ARP requests and other 892 "broadcast" messages. 894 Because of the inefficiencies of broadcasting in a Frame Relay 895 environment, a new address resolution variation was developed. It is 896 called Inverse ARP [11] and describes a method for resolving a 897 protocol address when the hardware address is already known. In 898 Frame Relay's case, the known hardware address is the DLCI. Using 899 Inverse ARP for Frame Relay follows the same pattern as ARP and RARP 900 use. That is the source hardware address is inserted at the 901 receiving station. 903 In our example, station A may use Inverse ARP to discover the 904 protocol address of the station associated with its DLCI 50. The 905 Inverse ARP request would be as follows: 907 InARP Request from A (DLCI 50) 908 ar$op 8 (InARP request) 909 ar$sha unknown 910 ar$spa pA 911 ar$tha 0x0C21 (DLCI 50) 912 ar$tpa unknown 914 When Station B receives this packet, it will modify the source 915 hardware address with the Q.922 address from the Frame Relay header. 916 This way, the InARP request from A will become: 918 ar$op 8 (InARP request) 919 ar$sha 0x1061 920 ar$spa pA 921 ar$tha 0x0C21 922 ar$tpa unknown. 924 Station B will format an Inverse ARP response and send it to station 925 A as it would for any ARP message. 927 Stations must be able to map more than one IP address in the same IP 928 subnet (CIDR address prefix) to a particular DLCI on a Frame Relay 929 interface. This need arises from applications such as remote access, 930 where servers must act as ARP proxies for many dial-in clients, each 931 assigned a unique IP address while sharing bandwidth on the same DLC. 932 The dynamic nature of such applications result in frequent address 933 association changes with no affect on the DLC's status as reported by 934 Frame Relay PVC Status Signaling. 936 As with any other interface that utilizes ARP, stations may learn the 937 associations between IP addresses and DLCIs by processing unsolicited 938 ("gratuitous") ARP requests that arrive on the DLC. If one station 939 (perhaps a terminal server or remote access server) wishes to inform 940 its peer station on the other end of a Frame Relay DLC of a new 941 association between an IP address and that PVC, it should send an 942 unsolicited ARP request with the source IP address equal to the 943 destination IP address, and both set to the new IP address being used 944 on the DLC. This allows a station to "announce" new client 945 connections on a particular DLCI. The receiving station must store 946 the new association, and remove any old existing association, if 947 necessary, from any other DLCI on the interface. 949 7. IP over Frame Relay 951 Internet Protocol [9] (IP) datagrams sent over a Frame Relay network 952 conform to the encapsulation described previously. Within this 953 context, IP could be encapsulated in two different ways. 955 1. NLPID value indicating IP 957 +-----------------------+-----------------------+ 958 | Q.922 Address | 959 +-----------------------+-----------------------+ 960 | Control (UI) 0x03 | NLPID 0xCC | 961 +-----------------------+-----------------------+ 962 | IP packet | 963 | . | 964 | . | 965 | . | 966 +-----------------------+-----------------------+ 968 2. NLPID value indicating SNAP 970 +-----------------------+-----------------------+ 971 | Q.922 Address | 972 +-----------------------+-----------------------+ 973 | Control (UI) 0x03 | pad 0x00 | 974 +-----------------------+-----------------------+ 975 | NLPID 0x80 | | SNAP Header 976 +-----------------------+ OUI = 0x00-00-00 + Indicating 977 | | IP 978 +-----------------------+-----------------------+ 979 | PID 0x0800 | 980 +-----------------------+-----------------------+ 981 | IP packet | 982 | . | 983 | . | 984 | . | 985 +-----------------------+-----------------------+ 987 Although both of these encapsulations are supported under the given 988 definitions, it is advantageous to select only one method as the 989 appropriate mechanism for encapsulating IP data. Therefore, IP data 990 shall be encapsulated using the NLPID value of 0xCC indicating IP as 991 shown in option 1 above. This (option 1) is more efficient in 992 transmission (48 fewer bits), and is consistent with the 993 encapsulation of IP in X.25. 995 8. Other Protocols over Frame Relay 997 As with IP encapsulation, there are alternate ways to transmit 998 various protocols within the scope of this definition. To eliminate 999 the conflicts, the SNAP encapsulation is only used if no NLPID value 1000 is defined for the given protocol. 1002 As an example of how this works, ISO CLNP has a NLPID defined (0x81). 1003 Therefore, the NLPID field will indicate ISO CLNP and the data packet 1004 will follow immediately. The frame would be as follows: 1006 +---------------------------------------------+ 1007 | Q.922 Address | 1008 +----------------------+----------------------+ 1009 | Control (UI) 0x03 | NLPID 0x81 (CLNP) | 1010 +----------------------+----------------------+ 1011 | remainder of CLNP packet | 1012 | . | 1013 | . | 1014 +---------------------------------------------+ 1016 In this example, the NLPID is used to identify the data packet as 1017 CLNP. It is also considered part of the CLNP packet and as such, the 1018 NLPID should not be removed before being sent to the upper layers for 1019 processing. The NLPID is not duplicated. 1021 Other protocols, such as IPX, do not have a NLPID value defined. As 1022 mentioned above, IPX would be encapsulated using the SNAP header. In 1023 this case, the frame would be as follows: 1025 +---------------------------------------------+ 1026 | Q.922 Address | 1027 +----------------------+----------------------+ 1028 | Control (UI) 0x03 | pad 0x00 | 1029 +----------------------+----------------------+ 1030 | NLPID 0x80 (SNAP) | OUI - 0x00 00 00 | 1031 +----------------------+ | 1032 | | 1033 +---------------------------------------------+ 1034 | PID 0x8137 | 1035 +---------------------------------------------+ 1036 | IPX packet | 1037 | . | 1038 | . | 1039 +---------------------------------------------+ 1041 9. Bridging Model for Frame Relay 1043 The model for bridging in a Frame Relay network is identical to the 1044 model for remote bridging as described in IEEE P802.1g "Remote MAC 1045 Bridging" [13] and supports the concept of "Virtual Ports". Remote 1046 bridges with LAN ports receive and transmit MAC frames to and from 1047 the LANs to which they are attached. They may also receive and 1048 transmit MAC frames through virtual ports to and from other remote 1049 bridges. A virtual port may represent an abstraction of a remote 1050 bridge's point of access to one, two or more other remote bridges. 1052 Remote Bridges are statically configured as members of a remote 1053 bridge group by management. All members of a remote bridge group are 1054 connected by one or more virtual ports. The set of remote MAC bridges 1055 in a remote bridge group provides actual or *potential* MAC layer 1056 interconnection between a set of LANs and other remote bridge groups 1057 to which the remote bridges attach. 1059 In a Frame Relay network there must be a full mesh of Frame Relay VCs 1060 between bridges of a remote bridge group. If the frame relay network 1061 is not a full mesh, then the bridge network must be divided into 1062 multiple remote bridge groups. 1064 The frame relay VCs that interconnect the bridges of a remote bridge 1065 group may be combined or used individually to form one or more 1066 virtual bridge ports. This gives flexibility to treat the Frame 1067 Relay interface either as a single virtual bridge port, with all VCs 1068 in a group, or as a collection of bridge ports (individual or grouped 1069 VCs). 1071 When a single virtual bridge port provides the interconnectivity for 1072 all bridges of a given remote bridge group (i.e. all VCs are combined 1073 into a single virtual port), the standard Spanning Tree Algorithm may 1074 be used to determine the state of the virtual port. When more than 1075 one virtual port is configured within a given remote bridge group 1076 then an "extended" Spanning Tree Algorithm is required. Such an 1077 extended algorithm is defined in IEEE 802.1g [13]. The operation of 1078 this algorithm is such that a virtual port is only put into backup if 1079 there is a loop in the network external to the remote bridge group. 1081 The simplest bridge configuration for a Frame Relay network is the 1082 LAN view where all VCs are combined into a single virtual port. 1083 Frames, such as BPDUs, which would be broadcast on a LAN, must be 1084 flooded to each VC (or multicast if the service is developed for 1085 Frame Relay services). Flooding is performed by sending the packet to 1086 each relevant DLC associated with the Frame Relay interface. The VCs 1087 in this environment are generally invisible to the bridge. That is, 1088 the bridge sends a flooded frame to the frame relay interface and 1089 does not "see" that the frame is being forwarded to each VC 1090 individually. If all participating bridges are fully connected (full 1091 mesh) the standard Spanning Tree Algorithm will suffice in this 1092 configuration. 1094 Typically LAN bridges learn which interface a particular end station 1095 may be reached on by associating a MAC address with a bridge port. 1096 In a Frame Relay network configured for the LAN-like single bridge 1097 port (or any set of VCs grouped together to form a single bridge 1098 port), however, the bridge must not only associated a MAC address 1099 with a bridge port, but it must also associate it with a connection 1100 identifier. For Frame Relay networks, this connection identifier is 1101 a DLCI. It is unreasonable and perhaps impossible to require bridges 1102 to statically configure an association of every possible destination 1103 MAC address with a DLC. Therefore, Frame Relay LAN-modeled bridges 1104 must provide a mechanism to allow the Frame Relay bridge port to 1105 dynamically learn the associations. To accomplish this dynamic 1106 learning, a bridged packet shall conform to the encapsulation 1107 described within section 4.2. In this way, the receiving Frame Relay 1108 interface will know to look into the bridged packet to gather the 1109 appropriate information. 1111 A second Frame Relay bridging approach, the point-to-point view, 1112 treats each Frame Relay VC as a separate bridge port. Flooding and 1113 forwarding packets are significantly less complicated using the 1114 point-to-point approach because each bridge port has only one 1115 destination. There is no need to perform artificial flooding or to 1116 associate DLCIs with destination MAC addresses. Depending upon the 1117 interconnection of the VCs, an extended Spanning Tree algorithm may 1118 be required to permit all virtual ports to remain active as long as 1119 there are no true loops in the topology external to the remote bridge 1120 group. 1122 It is also possible to combine the LAN view and the point-to-point 1123 view on a single Frame Relay interface. To do this, certain VCs are 1124 combined to form a single virtual bridge port while other VCs are 1125 independent bridge ports. 1127 The following drawing illustrates the different possible bridging 1128 configurations. The dashed lines between boxes represent virtual 1129 circuits. 1131 +-------+ 1132 -------------------| B | 1133 / -------| | 1134 / / +-------+ 1135 / | 1136 +-------+/ \ +-------+ 1137 | A | -------| C | 1138 | |-----------------------| | 1139 +-------+\ +-------+ 1140 \ 1141 \ +-------+ 1142 \ | D | 1143 -------------------| | 1144 +-------+ 1146 Since there is less than a full mesh of VCs between the bridges in 1147 this example, the network must be divided into more than one remote 1148 bridge group. A reasonable configuration is to have bridges A, B, 1149 and C in one group, and have bridges A and D in a second. 1151 Configuration of the first bridge group combines the VCs 1152 interconnection the three bridges (A, B, and C) into a single virtual 1153 port. This is an example of the LAN view configuration. The second 1154 group would also be a single virtual port which simply connects 1155 bridges A and D. In this configuration the standard Spanning Tree 1156 Algorithm is sufficient to detect loops. 1158 An alternative configuration has three individual virtual ports in 1159 the first group corresponding to the VCs interconnecting bridges A, B 1160 and C. Since the application of the standard Spanning Tree Algorithm 1161 to this configuration would detect a loop in the topology, an 1162 extended Spanning Tree Algorithm would have to be used in order for 1163 all virtual ports to be kept active. Note that the second group 1164 would still consist of a single virtual port and the standard 1165 Spanning Tree Algorithm could be used in this group. 1167 Using the same drawing, one could construct a remote bridge scenario 1168 with three bridge groups. This would be an example of the point-to- 1169 point case. Here, the VC connecting A and B, the VC connecting A and 1170 C, and the VC connecting A and D are all bridge groups with a single 1171 virtual port. 1173 10. Appendix A 1175 List of Commonly Used NLPIDs 1177 0x00 Null Network Layer or Inactive Set 1178 (not used with Frame Relay) 1179 0x08 Q.933 [2] 1180 0x80 SNAP 1181 0x81 ISO CLNP 1182 0x82 ISO ESIS 1183 0x83 ISO ISIS 1184 0x8E IPv6 1185 0xB0 FRF.9 Data Compression [14] 1186 0xB1 FRF.12 Fragmentation [18] 1187 0xCC IPv4 1188 0xCF PPP in Frame Relay [17] 1190 List of PIDs of OUI 00-80-C2 1192 with preserved FCS w/o preserved FCS Media 1193 ------------------ ----------------- -------------- 1194 0x00-01 0x00-07 802.3/Ethernet 1195 0x00-02 0x00-08 802.4 1196 0x00-03 0x00-09 802.5 1197 0x00-04 0x00-0A FDDI 1198 0x00-0B 802.6 1199 0x00-0D Fragments 1200 0x00-0E BPDUs as defined by 1201 802.1(d) or 1202 802.1(g)[12]. 1203 0x00-0F Source Routing BPDUs 1205 11. Appendix B - Connection Oriented Procedures 1207 This Appendix contains additional information and instructions for 1208 using ITU Recommendation Q.933 [2] and other ITU standards for 1209 encapsulating data over frame relay. The information contained here 1210 is similar (and in some cases identical) to that found in Annex E to 1211 ITU Q.933. The authoritative source for this information is in Annex 1212 E and is repeated here only for convenience. 1214 The Network Level Protocol ID (NLPID) field is administered by ISO 1215 and the ITU. It contains values for many different protocols 1216 including IP, CLNP (ISO 8473), ITU Q.933, and ISO 8208. A figure 1217 summarizing a generic encapsulation technique over frame relay 1218 networks follows. The scheme's flexibility consists in the 1219 identification of multiple alternative to identify different 1220 protocols used either by 1221 - end-to-end systems or 1222 - LAN to LAN bride and routers or 1223 - a combination of the above. 1225 over frame relay networks. 1227 Q.922 control 1228 | 1229 | 1230 -------------------------------------------- 1231 | | 1232 UI I Frame 1233 | | 1234 --------------------------------- -------------- 1235 | 0x08 | 0x81 |0xCC | 0x80 |..01.... |..10.... 1236 | | | | | | 1237 Q.933 CLNP IP SNAP ISO 8208 ISO 8208 1238 | | Modulo 8 Modulo 128 1239 | | 1240 -------------------- OUI 1241 | | | 1242 L2 ID L3 ID ------- 1243 | User | | 1244 | Specified | | 1245 | 0x70 802.3 802.6 1246 | 1247 --------------------------- 1248 |0x51 |0x4E | |0x4C |0x50 1249 | | | | | 1250 7776 Q.922 Others 802.2 User 1251 Specified 1253 For those protocols which do not have a NLPID assigned or do not have 1254 a SNAP encapsulation, the NLPID value of 0x08, indicating ITU 1255 Recommendation Q.933 should be used. The four octets following the 1256 NLPID include both layer 2 and layer 3 protocol identification. The 1257 code points for most protocols are currently defined in ITU Q.933 low 1258 layer compatibility information element. The code points for "User 1259 Specified" are described in Frame Relay Forum FRF.3.1 [15]. There is 1260 also an escape for defining non-standard protocols. 1262 Format of Other Protocols 1263 using Q.933 NLPID 1264 +-------------------------------+ 1265 | Q.922 Address | 1266 +---------------+---------------+ 1267 | Control 0x03 | NLPID 0x08 | 1268 +---------------+---------------+ 1269 | L2 Protocol ID | 1270 | octet 1 | octet 2 | 1271 +---------------+---------------+ 1272 | L3 Protocol ID | 1273 | octet 1 | octet 2 | 1274 +---------------+---------------+ 1275 | Protocol Data | 1276 +-------------------------------+ 1277 | FCS | 1278 +-------------------------------+ 1280 ISO 8802/2 with user specified 1281 layer 3 1282 +-------------------------------+ 1283 | Q.922 Address | 1284 +---------------+---------------+ 1285 | Control 0x03 | NLPID 0x08 | 1286 +---------------+---------------+ 1287 | 802/2 0x4C | 0x80 | 1288 +---------------+---------------+ 1289 |User Spec. 0x70| Note 1 | 1290 +---------------+---------------+ 1291 | DSAP | SSAP | 1292 +---------------+---------------+ 1293 | Control (Note 2) | 1294 +-------------------------------+ 1295 | Remainder of PDU | 1296 +-------------------------------+ 1297 | FCS | 1298 +-------------------------------+ 1300 Note 1: Indicates the code point for user specified 1301 layer 3 protocol. 1303 Note 2: Control field is two octets for I-format and 1304 S-format frames (see 88002/2) 1306 Encapsulations using I frame (layer 2) 1307 The Q.922 I frame is for supporting layer 3 protocols which require 1308 acknowledged data link layer (e.g., ISO 8208). The C/R bit will be 1309 used for command and response indications. 1311 Format of ISO 8208 frame 1312 Modulo 8 1313 +-------------------------------+ 1314 | Q.922 Address | 1315 +---------------+---------------+ 1316 | ....Control I frame | 1317 +---------------+---------------+ 1318 | 8208 packet (modulo 8) Note 3 | 1319 | | 1320 +-------------------------------+ 1321 | FCS | 1322 +-------------------------------+ 1324 Note 3: First octet of 8208 packet also identifies the 1325 NLPID which is "..01....". 1327 Format of ISO 8208 frame 1328 Modulo 128 1329 +-------------------------------+ 1330 | Q.922 Address | 1331 +---------------+---------------+ 1332 | ....Control I frame | 1333 +---------------+---------------+ 1334 | 8208 packet (modulo 128) | 1335 | Note 4 | 1336 +-------------------------------+ 1337 | FCS | 1338 +-------------------------------+ 1340 Note 4: First octet of 8208 packet also identifies the 1341 NLPID which is "..10....". 1343 12. Security Considerations 1345 This document contains two major functional specifications: 1346 mechanisms for identifying the multiprotocol encapsulation of 1347 datagrams, and the specification of how ARP and InARP are used over 1348 Frame Relay. 1350 For the former functionality, there is obviously an element in trust 1351 in any encapsulation protocol - a receiver must trust that the sender 1352 has correctly identified the protocol being encapsulated. In 1353 general, there is no way for a receiver to try to ascertain that the 1354 sender did indeed use the proper protocol identification, nor would 1355 this be desired functionality. 1357 For the latter functionality, this document specifies the use of the 1358 ARP family of protocols with Frame Relay, and is subject to the same 1359 security constraints that affect ARP and similar address resolution 1360 protocols. Because authentication is not a part of ARP, there are 1361 known security issues relating to its use (e.g., host impersonation). 1362 No additional security mechanisms have been added to the ARP family 1363 of protocols for use with Frame Relay networks. 1365 13. References 1367 [1] International Telecommunication Union, "ISDN Data Link Layer 1368 Specification for Frame Mode Bearer Services", ITU-T 1369 Recommendation Q.922, 1992. 1371 [2] International Telecommunication Union, "Signalling Specifications 1372 for Frame Mode Switched and Permanent Virtual Connection Control 1373 and Status Monitoring", ITU-T Recommendation Q.933, 1995. 1375 [3] Information technology - Telecommunications and Information 1376 Exchange between systems - Protocol Identification in the Network 1377 Layer, ISO/IEC TR 9577: 1992. 1379 [4] F. Baker, R. Bowen, "PPP Bridging Control Protocol (BCP)", RFC 1380 1638, ACC, June 1994. 1382 [5] International Standard, Information Processing Systems - Local 1383 Area Networks - Logical Link Control, ISO 8802-2, ANSI/IEEE, 1384 Second Edition, 1994-12-30. 1386 [6] Plummer, D., "An Ethernet Address Resolution Protocol - or - 1387 Converting Network Protocol Addresses to 48.bit Ethernet Address 1388 for Transmission on Ethernet Hardware", STD 37, RFC 826, MIT, 1389 November 1982. 1391 [7] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700, 1392 USC/Information Sciences Institute, October 1994 1394 [8] Finlayson, R., Mann, R., Mogul, J., and M. Theimer, "A Reverse 1395 Address Resolution Protocol", STD 38, RFC 903, Stanford 1396 University, June 1984. 1398 [9] Postel, J. and Reynolds, J., "A Standard for the Transmission of 1399 IP Datagrams over IEEE 802 Networks", RFC 1042, USC/Information 1400 Sciences Institute, February 1988. 1402 [10] IEEE, "IEEE Standard for Local and Metropolitan Area Networks: 1403 Overview and architecture", IEEE Standard 802-1990. 1405 [11] Bradley, T., and C. Brown, "Inverse Address Resolution Protocol", 1406 RFC 1293, Wellfleet Communications, Inc., January 1992. 1408 [12] IEEE, "IEEE Standard for Local and Metropolitan Networks: Media 1409 Access Control (MAC) Bridges", IEEE Standard 802.1D-1990. 1411 [13] ISO/IEC 15802-5 : 1998 (IEEE Standard 802.1G), Remote Media 1412 Access Control (MAC) Bridging, March 12, 1997. 1414 [14] Frame Relay Forum, "Data Compression Over Frame Relay 1415 Implementation Agreement", FRF.9, January 22, 1996. 1417 [15] Frame Relay Forum, "Multiprotocol Encapsulation Implementation 1418 Agreement", FRF.3.1, June 22, 1995. 1420 [16] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1421 Levels", BCP 14, RFC 2119, Harvard University, March 1997. 1423 [17] Simpson, W., "PPP in Frame Relay", RFC 1973, Daydreamer, June 1424 1996. 1426 [18] Frame Relay Forum, "Frame Relay Fragmentation Implementation 1427 Agreement", FRF.12, December 1997. 1429 14. Authors' Addresses 1431 Caralyn Brown 1432 FORE Systems, Inc. 1433 1 Corporate Drive 1434 Andover, MA 01810 1435 Phone: (978) 689-2400 x133 1436 Email: cbrown@fore.com 1438 Andrew Malis 1439 Ascend Communications, Inc. 1440 1 Robbins Road 1441 Westford, MA 01886 1442 Phone: (978) 952-7414 1443 Email: malis@ascend.com