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'15') (Obsoleted by RFC 4306) Summary: 5 errors (**), 0 flaws (~~), 8 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Draft L. Yang 2 Expiration: March 2004 Intel Corp. 3 File: draft-ietf-forces-framework-09.txt R. Dantu 4 Working Group: ForCES Univ. of North Texas 5 T. Anderson 6 Intel Corp. 7 R. Gopal 8 Nokia 10 September 2003 12 Forwarding and Control Element Separation (ForCES) Framework 14 draft-ietf-forces-framework-09.txt 16 Status of this Memo 18 This document is an Internet-Draft and is in full conformance with 19 all provisions of Section 10 of RFC2026. Internet-Drafts are 20 working documents of the Internet Engineering Task Force (IETF), 21 its areas, and its working groups. Note that other groups may also 22 distribute working documents as Internet-Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six 25 months and may be updated, replaced, or obsoleted by other 26 documents at any time. It is inappropriate to use Internet-Drafts 27 as reference material or to cite them other than as ``work in 28 progress.'' 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 Copyright Notice 38 Copyright (C) The Internet Society (2003). All Rights Reserved. 40 Abstract 42 This document defines the architectural framework for the ForCES 43 (Forwarding and Control Element Separation) network elements, and 44 identifies the associated entities and the interactions among them. 46 Table of Contents 47 1. Definitions...................................................3 48 2. Introduction to Forwarding and Control Element Separation 49 (ForCES).........................................................5 50 3. Architecture..................................................9 51 3.1. Control Elements and Fr Reference Point.................10 52 3.2. Forwarding Elements and Fi reference point..............11 53 3.3. CE Managers.............................................14 54 3.4. FE Managers.............................................14 55 4. Operational Phases...........................................15 56 4.1. Pre-association Phase...................................15 57 4.1.1. Fl Reference Point.................................15 58 4.1.2. Ff Reference Point.................................16 59 4.1.3. Fc Reference Point.................................17 60 4.2. Post-association Phase and Fp reference point...........17 61 4.2.1. Proximity and Interconnect between CEs and FEs.....17 62 4.2.2. Association Establishment..........................18 63 4.2.3. Steady-state Communication.........................19 64 4.2.4. Data Packets across Fp reference point.............20 65 4.2.5. Proxy FE...........................................21 66 4.3. Association Re-establishment............................21 67 4.3.1. CE graceful restart................................22 68 4.3.2. FE restart.........................................23 69 5. Applicability to RFC1812.....................................24 70 5.1. General Router Requirements.............................24 71 5.2. Link Layer..............................................26 72 5.3. Internet Layer Protocols................................26 73 5.4. Internet Layer Forwarding...............................27 74 5.5. Transport Layer.........................................28 75 5.6. Application Layer -- Routing Protocols..................28 76 5.7. Application Layer -- Network Management Protocol........28 77 6. Summary......................................................29 78 7. Acknowledgements.............................................29 79 8. Security Considerations......................................29 80 8.1. Analysis of Potential Threats Introduced by ForCES......30 81 8.1.1. "Join" or "Remove" Message Flooding on CEs.........30 82 8.1.2. Impersonation Attack...............................30 83 8.1.3. Replay Attack......................................30 84 8.1.4. Attack during Fail Over............................31 85 8.1.5. Data Integrity.....................................31 86 8.1.6. Data Confidentiality...............................31 87 8.1.7. Sharing security parameters........................32 88 8.1.8. Denial of Service Attack via External Interface....32 89 8.2. Security Recommendations for ForCES.....................32 90 8.2.1. Security Configuration.............................33 91 8.2.2. Using TLS with ForCES..............................33 92 8.2.3. Using IPsec with ForCES............................34 94 9. Normative References.........................................36 95 10. Informative References......................................36 96 11. Authors' Addresses..........................................37 97 12. Intellectual Property Right.................................38 98 13. Full Copyright Statement....................................38 100 Conventions used in this document 102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 104 this document are to be interpreted as described in RFC 2119. 106 1. Definitions 108 A set of terminology associated with the ForCES requirements is 109 defined in [3] and we only include the definitions that are most 110 relevant to this document here. 112 Addressable Entity (AE) - An entity that is directly addressable 113 given some interconnect technology. For example, on IP networks, 114 it is a device to which we can communicate using an IP address; on 115 a switch fabric, it is a device to which we can communicate using a 116 switch fabric port number. 118 Physical Forwarding Element (PFE) - An AE that includes hardware 119 used to provide per-packet processing and handling. This hardware 120 may consist of (but is not limited to) network processors, ASICs 121 (Application-Specific Integrated Circuits), or general purpose 122 processors, installed on line cards, daughter boards, mezzanine 123 cards, or in stand-alone boxes. 125 PFE Partition - A logical partition of a PFE consisting of some 126 subset of each of the resources (e.g., ports, memory, forwarding 127 table entries) available on the PFE. This concept is analogous to 128 that of the resources assigned to a virtual switching element as 129 described in [8]. 131 Physical Control Element (PCE) - An AE that includes hardware used 132 to provide control functionality. This hardware typically includes 133 a general purpose processor. 135 PCE Partition - A logical partition of a PCE consisting of some 136 subset of each of the resources available on the PCE. 138 Forwarding Element (FE) - A logical entity that implements the 139 ForCES protocol. FEs use the underlying hardware to provide per- 140 packet processing and handling as directed by a CE via the ForCES 141 protocol. FEs may happen to be a single blade (or PFE), a 142 partition of a PFE or multiple PFEs. 144 Control Element (CE) - A logical entity that implements the ForCES 145 protocol and uses it to instruct one or more FEs how to process 146 packets. CEs handle functionality such as the execution of control 147 and signaling protocols. CEs may consist of PCE partitions or 148 whole PCEs. 150 ForCES Network Element (NE) - An entity composed of one or more CEs 151 and one or more FEs. To entities outside an NE, the NE represents 152 a single point of management. Similarly, an NE usually hides its 153 internal organization from external entities. 155 Pre-association Phase - The period of time during which an FE 156 Manager (see below) and a CE Manager (see below) are determining 157 which FE and CE should be part of the same network element. 159 Post-association Phase - The period of time during which an FE does 160 know which CE is to control it and vice versa, including the time 161 during which the CE and FE are establishing communication with one 162 another. 164 ForCES Protocol - While there may be multiple protocols used within 165 the overall ForCES architecture, the term "ForCES protocol" refers 166 only to the ForCES post-association phase protocol (see below). 168 ForCES Post-Association Phase Protocol - The protocol used for 169 post-association phase communication between CEs and FEs. This 170 protocol does not apply to CE-to-CE communication, FE-to-FE 171 communication, nor to communication between FE and CE managers. 172 The ForCES protocol is a master-slave protocol in which FEs are 173 slaves and CEs are masters. This protocol includes both the 174 management of the communication channel (e.g., connection 175 establishment, heartbeats) and the control messages themselves. 176 This protocol could be a single protocol or could consist of 177 multiple protocols working together, and may be unicast based or 178 multicast based. A separate protocol document will specify this 179 information. 181 FE Manager - A logical entity that operates in the pre-association 182 phase and is responsible for determining to which CE(s) an FE 183 should communicate. This process is called CE discovery and may 184 involve the FE manager learning the capabilities of available CEs. 185 An FE manager may use anything from a static configuration to a 186 pre-association phase protocol (see below) to determine which CE(s) 187 to use; however, this is currently out of scope. Being a logical 188 entity, an FE manager might be physically combined with any of the 189 other logical entities mentioned in this section. 191 CE Manager - A logical entity that operates in the pre-association 192 phase and is responsible for determining to which FE(s) a CE should 193 communicate. This process is called FE discovery and may involve 194 the CE manager learning the capabilities of available FEs. A CE 195 manager may use anything from a static configuration to a pre- 196 association phase protocol (see below) to determine which FE to 197 use, however this is currently out of scope. Being a logical 198 entity, a CE manager might be physically combined with any of the 199 other logical entities mentioned in this section. 201 Pre-association Phase Protocol - A protocol between FE managers and 202 CE managers that is used to determine which CEs or FEs to use. A 203 pre-association phase protocol may include a CE and/or FE 204 capability discovery mechanism. Note that this capability 205 discovery process is wholly separate from (and does not replace) 206 that used within the ForCES protocol. However, the two capability 207 discovery mechanisms may utilize the same FE model. 209 FE Model - A model that describes the logical processing functions 210 of an FE. 212 ForCES Protocol Element - An FE or CE. 214 Intra-FE topology - - Representation of how a single FE is realized 215 by combining possibly multiple logical functional blocks along 216 multiple data path. This is defined by the FE model. 218 FE Topology -- Representation of how the multiple FEs in a single 219 NE are interconnected. Sometimes it is called inter-FE topology, 220 to be distinguished from intra-FE topology used by the FE model. 222 Inter-FE topology - see FE Topology. 224 2. Introduction to Forwarding and Control Element Separation (ForCES) 226 An IP network element (NE) appears to external entities as a 227 monolithic piece of network equipment, e.g., a router, NAT, 228 firewall, or load balancer. Internally, however, an IP network 229 element (NE) (such as a router) is composed of numerous logically 230 separated entities that cooperate to provide a given functionality 231 (such as routing). Two types of network element components exist: 232 control element (CE) in control plane and forwarding element (FE) 233 in forwarding plane (or data plane). Forwarding elements typically 234 are ASIC, network-processor, or general-purpose processor-based 235 devices that handle data path operations for each packet. Control 236 elements are typically based on general-purpose processors that 237 provide control functionality like routing and signaling protocols. 239 ForCES aims to define a framework and associated protocol(s) to 240 standardize information exchange between the control and forwarding 241 plane. Having standard mechanisms allows CEs and FEs to become 242 physically separated standard components. This physical separation 243 accrues several benefits to the ForCES architecture. Separate 244 components would allow component vendors to specialize in one 245 component without having to become experts in all components. 246 Standard protocol also allows the CEs and FEs from different 247 component vendors to interoperate with each other and hence it 248 becomes possible for system vendors to integrate together the CEs 249 and FEs from different component suppliers. This interoperability 250 translates into more design choices and flexibility for the system 251 vendors. Overall, ForCES will enable rapid innovation in both the 252 control and forwarding planes while maintaining interoperability. 253 Scalability is also easily provided by this architecture in that 254 additional forwarding or control capacity can be added to existing 255 network elements without the need for forklift upgrades. 257 ------------------------- ------------------------- 258 | Control Blade A | | Control Blade B | 259 | (CE) | | (CE) | 260 ------------------------- ------------------------- 261 ^ | ^ | 262 | | | | 263 | V | V 264 --------------------------------------------------------- 265 | Switch Fabric Backplane | 266 --------------------------------------------------------- 267 ^ | ^ | ^ | 268 | | | | . . . | | 269 | V | V | V 270 ------------ ------------ ------------ 271 |Router | |Router | |Router | 272 |Blade #1 | |Blade #2 | |Blade #N | 273 | (FE) | | (FE) | | (FE) | 274 ------------ ------------ ------------ 275 ^ | ^ | ^ | 276 | | | | . . . | | 277 | V | V | V 279 Figure 1. A router configuration example with separate blades. 281 One example of such physical separation is at the blade level. 282 Figure 1 shows such an example configuration of a router, with two 283 control blades and multiple forwarding blades, all interconnected 284 into a switch fabric backplane. In such a chassis configuration, 285 the control blades are the CEs while the router blades are FEs, and 286 the switch fabric backplane provides the physical interconnect for 287 all the blades. Control blade A may be the primary CE while 288 control blade B may be the backup CE providing redundancy. It is 289 also possible to have a redundant switch fabric for high 290 availability support. Routers today with this kind of 291 configuration use proprietary interfaces for messaging between CEs 292 and FEs. The goal of ForCES is to replace such proprietary 293 interfaces with a standard protocol. With a standard protocol like 294 ForCES implemented on all blades, it becomes possible for control 295 blades from vendor X and forwarding blades from vendor Y to work 296 seamlessly together in one chassis. 298 ------- ------- 299 | CE1 | | CE2 | 300 ------- ------- 301 ^ ^ 302 | | 303 V V 304 ============================================ Ethernet 305 ^ ^ . . . ^ 306 | | | 307 V V V 308 ------- ------- -------- 309 | FE#1| | FE#2| | FE#n | 310 ------- ------- -------- 311 ^ | ^ | ^ | 312 | | | | | | 313 | V | V | V 315 Figure 2. A router configuration example with separate boxes. 317 Another level of physical separation between the CEs and FEs can be 318 at the box level. In such configuration, all the CEs and FEs are 319 physically separated boxes, interconnected with some kind of high 320 speed LAN connection (like Gigabit Ethernet). These separated CEs 321 and FEs are only one hop away from each other within a local area 322 network. The CEs and FEs communicate to each other by running 323 ForCES, and the collection of these CEs and FEs together become one 324 routing unit to the external world. Figure 2 shows such an example. 326 In both examples shown here, the same physical interconnect is used 327 for both CE-to-FE and FE-to-FE communication. However, that does 328 not have to be the case. One reason to use different interconnects 329 is that CE-to-FE interconnect does not have to be as fast as the 330 FE-to-FE interconnect, so the more expensive fast connections can 331 be saved for FE-to-FE. The separate interconnects may also provide 332 reliability and redundancy benefits for the NE. 334 Some examples of control functions that can be implemented in the 335 CE include routing protocols like RIP, OSPF and BGP, control and 336 signaling protocols like RSVP (Resource Reservation Protocol), LDP 337 (Label Distribution Protocol) for MPLS, etc. Examples of 338 forwarding functions in the FE include LPM (longest prefix match) 339 forwarder, classifiers, traffic shaper, meter, NAT (Network Address 340 Translators), etc. Figure 3 provides example functions in both CE 341 and FE. Any given NE may contain one or many of these CE and FE 342 functions in it. The diagram also shows that ForCES protocol is 343 used to transport both the control messages for ForCES itself and 344 the data packets that are originated/destined from/to the control 345 functions in CE (e.g., routing packets). Section 4.2.4 provides 346 more detail on this. 348 ------------------------------------------------- 349 | | | | | | | 350 |OSPF |RIP |BGP |RSVP |LDP |. . . | 351 | | | | | | | 352 ------------------------------------------------- 353 | ForCES Interface | 354 ------------------------------------------------- 355 ^ ^ 356 ForCES | |data 357 control | |packets 358 messages| |(e.g., routing packets) 359 v v 360 ------------------------------------------------- 361 | ForCES Interface | 362 ------------------------------------------------- 363 | | | | | | | 364 |LPM Fwd|Meter |Shaper |NAT |Classi-|. . . | 365 | | | | |fier | | 366 ------------------------------------------------- 367 | FE resources | 368 ------------------------------------------------- 370 Figure 3. Examples of CE and FE functions 372 A set of requirements for control and forwarding separation is 373 identified in [3]. This document describes a ForCES architecture 374 that satisfies the architectural requirements of that document and 375 defines a framework for ForCES network elements and the associated 376 entities to facilitate protocol definition. Whenever necessary, 377 this document uses many examples to illustrate the issues and/or 378 possible solutions in ForCES. These examples are intended to be 379 just examples, and should not be taken as the only or definite ways 380 of doing certain things. It is expected that separate document 381 will be produced by the ForCES working group to specify the ForCES 382 protocol(s). 384 3. Architecture 386 This section defines the ForCES architectural framework and the 387 associated logical components. This ForCES framework defines 388 components of ForCES NEs including several ancillary components. 389 These components may be connected in different kinds of topologies 390 for flexible packet processing. 392 --------------------------------------- 393 | ForCES Network Element | 394 -------------- Fc | -------------- -------------- | 395 | CE Manager |---------+-| CE 1 |------| CE 2 | | 396 -------------- | | | Fr | | | 397 | | -------------- -------------- | 398 | Fl | | | Fp / | 399 | | Fp| |----------| / | 400 | | | |/ | 401 | | | | | 402 | | | Fp /|----| | 403 | | | /--------/ | | 404 -------------- Ff | -------------- -------------- | 405 | FE Manager |---------+-| FE 1 | Fi | FE 2 | | 406 -------------- | | |------| | | 407 | -------------- -------------- | 408 | | | | | | | | | | 409 ----+--+--+--+----------+--+--+--+----- 410 | | | | | | | | 411 | | | | | | | | 412 Fi/f Fi/f 414 Figure 4. ForCES Architectural Diagram 416 The diagram in Figure 4 shows the logical components of the ForCES 417 architecture and their relationships. There are two kinds of 418 components inside a ForCES network element: control element (CE) 419 and forwarding element (FE). The framework allows multiple 420 instances of CE and FE inside one NE. Each FE contains one or more 421 physical media interfaces for receiving and transmitting packets 422 from/to the external world. The aggregation of these FE interfaces 423 becomes the NE's external interfaces. In addition to the external 424 interfaces, there must also exist some kind of interconnect within 425 the NE so that the CE and FE can communicate with each other, and 426 one FE can forward packets to another FE. The diagram also shows 427 two entities outside of the ForCES NE: CE Manager and FE Manager. 428 These two entities provide configuration to the corresponding CE or 429 FE in the pre-association phase (see Section 4.1). There is no 430 defined role for FE Manager and CE Manager in post-association 431 phase, thus these logical components are not considered part of the 432 ForCES NE. 434 For convenience, the logical interactions between these components 435 are labeled by reference points Fp, Fc, Ff, Fr, Fl, and Fi, as 436 shown in Figure 4. The FE external interfaces are labeled as Fi/f. 437 More detail is provided in Section 3 and 4 for each of these 438 reference points. All these reference points are important in 439 understanding the ForCES architecture, however, the ForCES protocol 440 is only defined over one reference point -- Fp. 442 The interface between two ForCES NEs is identical to the interface 443 between two conventional routers and these two NEs exchange the 444 protocol packets through the external interfaces at Fi/f. ForCES 445 NEs connect to existing routers transparently. 447 3.1. Control Elements and Fr Reference Point 449 It is not necessary to define any protocols across the Fr reference 450 point to enable control and forwarding separation for simple 451 configurations like single CE and multiple FEs. However, this 452 architecture permits multiple CEs to be present in a network 453 element. In cases where an implementation uses multiple CEs, the 454 invariant that the CEs and FEs together appear as a single NE must 455 be maintained. 457 Multiple CEs may be used for redundancy, load sharing, distributed 458 control, or other purposes. Redundancy is the case where one or 459 more CEs are prepared to take over should an active CE fail. Load 460 sharing is the case where two or more CEs are concurrently active 461 and any request that can be serviced by one of the CEs can also be 462 serviced by any of the other CEs. For both redundancy and load 463 sharing, the CEs involved are equivalently capable. The only 464 difference between these two cases is in terms of how many active 465 CEs there are. Distributed control is the case where two or more 466 CEs are concurrently active but certain requests can only be 467 serviced by certain CEs. 469 When multiple CEs are employed in a ForCES NE, their internal 470 organization is considered an implementation issue that is beyond 471 the scope of ForCES. CEs are wholly responsible for coordinating 472 amongst themselves via the Fr reference point to provide 473 consistency and synchronization. However, ForCES does not define 474 the implementation or protocols used between CEs, nor does it 475 define how to distribute functionality among CEs. Nevertheless, 476 ForCES will support mechanisms for CE redundancy or fail over, and 477 it is expected that vendors will provide redundancy or fail over 478 solutions within this framework. 480 3.2. Forwarding Elements and Fi reference point 482 An FE is a logical entity that implements the ForCES protocol and 483 uses the underlying hardware to provide per-packet processing and 484 handling as directed by a CE. It is possible to partition one 485 physical FE into multiple logical FEs. It is also possible for one 486 FE to use multiple physical FEs. The mapping between physical 487 FE(s) and the logical FE(s) is beyond the scope of ForCES. For 488 example, a logical partition of a physical FE can be created by 489 assigning some portion of each of the resources (e.g., ports, 490 memory, forwarding table entries) available on the physical FE to 491 each of the logical FEs. Such concept of FE virtualization is 492 analogous to a virtual switching element as described in [8]. If 493 FE virtualization occurs only in the pre-association phase, it has 494 no impact on ForCES. However, if FE virtualization results in 495 dynamic resource change on FE during post-associaiton phase, the FE 496 model needs to be able to report such capability and the ForCES 497 protocol needs to be able to inform the CE of such change via 498 asynchronous messages (see [3], Section 5, requirement #6). 500 FEs perform all packet processing functions as directed by CEs. 501 FEs have no initiative of their own. Instead, FEs are slaves and 502 only do as they are told. FEs may communicate with one or more CEs 503 concurrently across reference point Fp. FEs have no notion of CE 504 redundancy, load sharing, or distributed control. Instead, FEs 505 accept commands from any CE authorized to control them, and it is 506 up to the CEs to coordinate among themselves to achieve redundancy, 507 load sharing or distributed control. The idea is to keep FEs as 508 simple and dumb as possible so that FEs can focus their resource on 509 the packet processing functions. 511 For example, in Figure 5, FE1 and FE2 can be configured to accept 512 commands from both the primary CE (CE1) and the backup CE (CE2). 513 Upon detection of CE1 failure, perhaps across the Fr or Fp 514 reference point, CE2 is configured to take over activities of CE1. 515 This is beyond the scope of ForCES and is not discussed further. 517 Distributed control can be achieved in the similar fashion, without 518 much intelligence on the part of FEs. For example, FEs can be 519 configured to detect RSVP and BGP protocol packets, and forward 520 RSVP packets to one CE and BGP packets to another CE. Hence, FEs 521 may need to do packet filtering for forwarding packets to specific 522 CEs. 524 ------- Fr ------- 525 | CE1 | ------| CE2 | 526 ------- ------- 527 | \ / | 528 | \ / | 529 | \ / | 530 | \/Fp | 531 | /\ | 532 | / \ | 533 | / \ | 534 ------- Fi ------- 535 | FE1 |<----->| FE2 | 536 ------- ------- 538 Figure 5. CE redundancy example. 540 This architecture permits multiple FEs to be present in an NE. [3] 541 dictates that the ForCES protocol must be able to scale to at least 542 hundreds of FEs (see [3] Section 5, requirement #11). Each of 543 these FEs may potentially have a different set of packet processing 544 functions, with different media interfaces. FEs are responsible 545 for basic maintenance of layer-2 connectivity with other FEs and 546 with external entities. Many layer-2 media include sophisticated 547 control protocols. The FORCES protocol (over the Fp reference 548 point) will be able to carry messages for such protocols so that, 549 in keeping with the dumb FE model, the CE can provide appropriate 550 intelligence and control over these media. 552 When multiple FEs are present, ForCES requires that packets must be 553 able to arrive at the NE by one FE and leave the NE via a different 554 FE (See [3], Section 5, Requirement #3). Packets that enter the NE 555 via one FE and leave the NE via a different FE are transferred 556 between FEs across the Fi reference point. Fi reference point 557 could be used by FEs to discovery their (inter-FE) topology, 558 perhaps during pre-association phase. The Fi reference point is a 559 separate protocol from the Fp reference point and is not currently 560 defined by the ForCES architecture. 562 FEs could be connected in different kinds of topologies and packet 563 processing may spread across several FEs in the topology. Hence, 564 logical packet flow may be different from physical FE topology. 565 Figure 6 provides some topology examples. When it is necessary to 566 forward packets between FEs, the CE needs to understand the FE 567 topology. The FE topology may be queried from the FEs by the CEs 568 via ForCES protocol, but the FEs are not required to provide that 569 information to the CEs. So, the FE topology information may also be 570 gathered by other means outside of the ForCES protocol (like inter- 571 FE topology discovery protocol). 573 ----------------- 574 | CE | 575 ----------------- 576 ^ ^ ^ 577 / | \ 578 / v \ 579 / ------- \ 580 / +->| FE3 |<-+ \ 581 / | | | | \ 582 v | ------- | v 583 ------- | | ------- 584 | FE1 |<-+ +->| FE2 | 585 | |<--------------->| | 586 ------- ------- 587 ^ | ^ | 588 | | | | 589 | v | v 591 (a) Full mesh among FE1, FE2 and FE3. 593 ----------- 594 | CE | 595 ----------- 596 ^ ^ ^ ^ 597 / | | \ 598 /------ | | ------\ 599 v v v v 600 ------- ------- ------- ------- 601 | FE1 |<->| FE2 |<->| FE3 |<->| FE4 | 602 ------- ------- ------- ------- 603 ^ | ^ | ^ | ^ | 604 | | | | | | | | 605 | v | v | v | v 606 (b) Multiple FEs in a daisy chain 608 ^ | 609 | v 610 ----------- 611 | FE1 |<-----------------------| 612 ----------- | 613 ^ ^ | 614 / \ | 615 | ^ / \ ^ | V 616 v | v v | v ---------- 617 --------- --------- | | 618 | FE2 | | FE3 |<------------>| CE | 619 --------- --------- | | 620 ^ ^ ^ ---------- 621 | \ / ^ ^ 622 | \ / | | 623 | v v | | 624 | ----------- | | 625 | | FE4 |<----------------------| | 626 | ----------- | 627 | | ^ | 628 | v | | 629 | | 630 |----------------------------------------| 632 (c) Multiple FEs connected by a ring 634 Figure 6. Some examples of FE topology. 636 3.3.CE Managers 638 CE managers are responsible for determining which FEs a CE should 639 control. It is legitimate for CE managers to be hard-coded with 640 the knowledge of with which FEs its CEs should communicate with. A 641 CE manager may also be physically embedded into a CE and be 642 implemented as a simple keypad or other direct configuration 643 mechanism on the CE. Finally, CE managers may be physically and 644 logically separate entities that configure the CE with FE 645 information via such mechanisms as COPS-PR [6] or SNMP [4]. 647 3.4. FE Managers 649 FE managers are responsible for determining with which CE any 650 particular FE should initially communicate. Like CE managers, no 651 restrictions are placed on how an FE manager decides with which CE 652 its FEs should communicate, nor are restrictions placed on how FE 653 managers are implemented. Each FE should have one and only one FE 654 manager, while different FEs may have the same or different FE 655 manager(s). Each manager can choose to exist and operate 656 independently of other manager. 658 4. Operational Phases 660 Both FEs and CEs require some configuration in place before they 661 can start information exchange and function as a coherent network 662 element. Two operational phases are identified in this framework: 663 pre-association and post-association. 665 4.1.Pre-association Phase 667 Pre-association phase is the period of time during which an FE 668 Manager and a CE Manager are determining which FE and CE should be 669 part of the same network element. The protocols used during this 670 phase may include all or some of the message exchange over Fl, Ff 671 and Fc reference points. However, all these may be optional and 672 none of this is within the scope of ForCES protocol. 674 4.1.1. Fl Reference Point 676 CE managers and FE managers may communicate across the Fl reference 677 point in the pre-association phase in order to determine which CEs 678 and FEs should communicate with each other. Communication across 679 the Fl reference point is optional in this architecture. No 680 requirements are placed on this reference point. 682 CE managers and FE managers may be operated by different entities. 683 The operator of the CE manager may not want to divulge, except to 684 specified FE managers, any characteristics of the CEs it manages. 685 Similarly, the operator of the FE manager may not want to divulge 686 FE characteristics, except to authorized entities. As such, CE 687 managers and FE managers may need to authenticate one another. 688 Subsequent communication between CE managers and FE managers may 689 require other security functions such as privacy, non-repudiation, 690 freshness, and integrity. 692 FE Manager FE CE Manager CE 693 | | | | 694 | | | | 695 |(security exchange) | | 696 1|<------------------------------>| | 697 | | | | 698 |(a list of CEs and their attributes) | 699 2|<-------------------------------| | 700 | | | | 701 |(a list of FEs and their attributes) | 702 3|------------------------------->| | 703 | | | | 704 | | | | 705 |<----------------Fl------------>| | 707 Figure 7. An example of message exchange over Fl reference point 709 Once the necessary security functions have been performed, the CE 710 and FE managers communicate to determine which CEs and FEs should 711 communicate with each other. At the very minimum, the CE and FE 712 managers need to learn of the existence of available FEs and CEs 713 respectively. This discovery process may entail one or both 714 managers learning the capabilities of the discovered ForCES 715 protocol elements. Figure 7 shows an example of possible message 716 exchange between CE manager and FE manager over Fl reference point. 718 4.1.2. Ff Reference Point 720 The Ff reference point is used to inform forwarding elements of the 721 association decisions made by the FE manager in pre-association 722 phase. Only authorized entities may instruct an FE with respect to 723 which CE should control it. Therefore, privacy, integrity, 724 freshness, and authentication are necessary between the FE manager 725 and FEs when the FE manager is remote to the FE. Once the 726 appropriate security has been established, the FE manager instructs 727 the FEs across this reference point to join a new NE or to 728 disconnect from an existing NE. The FE Manager could also assign 729 unique FE identifiers to the FEs using this reference point. The 730 FE identifiers are useful in post association phase to express FE 731 topology. Figure 8 shows example of message exchange over Ff 732 reference point. 734 FE Manager FE CE Manager CE 735 | | | | 736 | | | | 737 |(security exchange) |(security exchange) 738 1|<------------>|authentication 1|<----------->|authentication 739 | | | | 740 |(FE ID, attributes) |(CE ID, attributes) 741 2|<-------------|request 2|<----------->|request 742 | | | | 743 3|------------->|response 3|------------>|response 744 |(corresponding CE ID) |(corresponding FE ID) 745 | | | | 746 | | | | 747 |<-----Ff----->| |<-----Fc---->| 749 Figure 8. Examples of message exchange 750 over Ff and Fc reference points. 752 Note that the FE manager function may be co-located with the FE 753 (such as by manual keypad entry of the CE IP address), in which 754 case this reference point is reduced to a built-in function. 756 4.1.3. Fc Reference Point 758 The Fc reference point is used to inform control elements of the 759 association decisions made by CE managers in pre-association phase. 760 When the CE manager is remote, only authorized entities may 761 instruct a CE to control certain FEs. Privacy, integrity, 762 freshness and authentication are also required across this 763 reference point in such a configuration. Once appropriate security 764 has been established, the CE manager instructs CEs as to which FEs 765 they should control and how they should control them. Figure 8 766 shows example of message exchange over Fc reference point. 768 As with the FE manager and FEs, configurations are possible where 769 the CE manager and CE are co-located and no protocol is used for 770 this function. 772 4.2. Post-association Phase and Fp reference point 774 Post-association phase is the period of time during which an FE and 775 CE have been configured with information necessary to contact each 776 other and includes both association establishment and steady-state 777 communication. The communication between CE and FE is performed 778 across the Fp ("p" meaning protocol) reference point. ForCES 779 protocol is exclusively used for all communication across the Fp 780 reference point. 782 4.2.1. Proximity and Interconnect between CEs and FEs 784 The ForCES Working Group has made a conscious decision that the 785 first version of ForCES will be focused on "very close" CE/FE 786 localities in IP networks. Very Close localities consist of control 787 and forwarding elements that either are components in the same 788 physical box, or are separated at most by one local network hop 789 ([7]). CEs and FEs can be connected by a variety of interconnect 790 technologies, including Ethernet connections, backplanes, ATM 791 (cell) fabrics, etc. ForCES should be able to support each of 792 these interconnects (see [3] Section 5, requirement #1). When the 793 CEs and FEs are separated beyond a single L3 routing hop, the 794 ForCES protocol will make use of an existing RFC2914 compliant L4 795 protocol with adequate reliability, security and congestion control 796 (e.g. TCP, SCTP) for transport purposes. 798 4.2.2. Association Establishment 800 FE CE 801 | | 802 |(Security exchange.) | 803 1|<--------------------->| 804 | | 805 |(Let me join the NE please.) 806 2|---------------------->| 807 | | 808 |(What kind of FE are you? -- capability query) 809 3|<----------------------| 810 | | 811 |(Here is my FE functions/state: use model to 812 describe) 813 4|---------------------->| 814 | | 815 |(How are you connected with other FEs?) 816 5|<----------------------| 817 | | 818 |(Here is the FE topology info) 819 6|---------------------->| 820 | | 821 |(Initial config for FE -- optional) 822 7|<----------------------| 823 | | 824 |(I am ready to go. Shall I?) 825 8|---------------------->| 826 | | 827 |(Go ahead!) | 828 9|<----------------------| 829 | | 831 Figure 9. Example of message exchange between CE and FE 832 over Fp to establish NE association 834 As an example, figure 9 shows some of the message exchange that may 835 happen before the association between the CE and FE is fully 836 established. Either the CE or FE can initiate the connection. 837 Security handshake is necessary to authenticate the two 838 communication endpoints to each other before any further message 839 exchange can happen. The exact details of the security handshake 840 depend on the security solution chosen by ForCES protocol. Section 841 8 provides more details on the security considerations for ForCES. 842 After the successful security handshake, the FE needs to inform the 843 CE of its own capability and its topology in relation to other FEs. 844 The capability of the FE is represented by the FE model, described 845 in a separate document. The model would allow an FE to describe 846 what kind of packet processing functions it contains, in what order 847 the processing happens, what kinds of configurable parameters it 848 allows, what statistics it collects and what events it might throw, 849 etc. Once such information is available to the CE, the CE may 850 choose to send some initial or default configuration to the FE so 851 that the FE can start receiving and processing packets correctly. 852 Such initialization may not be necessary if the FE already obtains 853 the information from its own bootstrap process. Once FE starts 854 accepting packets for processing, we say the association of this FE 855 with its CE is now established. From then on, the CE and FE enter 856 steady-state communication. 858 4.2.3. Steady-state Communication 860 Once an association is established between the CE and FE, the 861 ForCES protocol is used by the CE and FE over Fp reference point to 862 exchange information to facilitate packet processing. 864 FE CE 865 | | 866 |(Add these new routes.)| 867 1|<----------------------| 868 | | 869 |(Successful.) | 870 2|---------------------->| 871 | | 872 | | 873 |(Query some stats.) | 874 1|<----------------------| 875 | | 876 |(Reply with stats collected.) 877 2|---------------------->| 878 | | 879 | | 880 |(My port is down, with port #.) 881 1|---------------------->| 882 | | 883 |(Here is a new forwarding table) 884 2|<----------------------| 885 | | 886 Figure 10. Examples of message exchange between CE and FE 887 over Fp during steady-state communication 889 Based on the information acquired through CEs' control processing, 890 CEs will frequently need to manipulate the packet-forwarding 891 behaviors of their FE(s) by sending instructions to FEs. For 892 example, Figure 10 shows message exchange examples in which the CE 893 sends new routes to the FE so that the FE can add them to its 894 forwarding table. The CE may query the FE for statistics collected 895 by the FE and the FE may notify the CE of important events such as 896 port failure. 898 4.2.4. Data Packets across Fp reference point 900 --------------------- ---------------------- 901 | | | | 902 | +--------+ | | +--------+ | 903 | |CE(BGP) | | | |CE(BGP) | | 904 | +--------+ | | +--------+ | 905 | | | | ^ | 906 | |Fp | | |Fp | 907 | v | | | | 908 | +--------+ | | +--------+ | 909 | | FE | | | | FE | | 910 | +--------+ | | +--------+ | 911 | | | | ^ | 912 | Router | | | Router | | 913 | A | | | B | | 914 ---------+----------- -----------+---------- 915 v ^ 916 | | 917 | | 918 ------------------->--------------- 920 Figure 11. Example to show data packet flow between two NEs. 922 Control plane protocol packets (such as RIP, OSPF messages) 923 addressed to any of NE's interfaces are typically redirected by the 924 receiving FE to its CE, and CE may originate packets and have its 925 FE deliver them to other NEs. Therefore, ForCES protocol over Fp 926 not only transports the ForCES protocol messages between CEs and 927 FEs, but also encapsulates the data packets from control plane 928 protocols. Moreover, one FE may be controlled by multiple CEs for 929 distributed control. In this configuration, the control protocols 930 supported by the FORCES NEs may spread across multiple CEs. For 931 example, one CE may support routing protocols like OSPF and BGP, 932 while a signaling and admission control protocol like RSVP is 933 supported in another CE. FEs are configured to recognize and 934 filter these protocol packets and forward them to the corresponding 935 CE. 937 Figure 11 shows one example of how the BGP packets originated by 938 router A are passed to router B. In this example, the ForCES 939 protocol is used to transport the packets from the CE to the FE 940 inside router A, and then from the FE to the CE inside router B. 941 In light of the fact that the ForCES protocol is responsible for 942 transporting both the control messages and the data packets between 943 the CE and FE over Fp reference point, it is possible to use either 944 a single protocol or multiple protocols to achieve this. 946 4.2.5. Proxy FE 948 In the case where a physical FE cannot implement (e.g., due to the 949 lack of a general purpose CPU) the ForCES protocol directly, a 950 proxy FE can be used in the middle of Fp reference point. This 951 allows the CE communicate to the physical FE via the proxy by using 952 ForCES, while the proxy manipulates the physical FE using some 953 intermediary form of communication (e.g., a non-ForCES protocol or 954 DMA). In such an implementation, the combination of the proxy and 955 the physical FE becomes one logical FE entity. 957 4.3. Association Re-establishment 959 FEs and CEs may join and leave NEs dynamically (see [3] Section 5, 960 requirements #12). When an FE or CE leaves the NE, the association 961 with the NE is broken. If the leaving party rejoins an NE later, 962 to re-establish the association, it may need to re-enter the pre- 963 association phase. Loss of association can also happen 964 unexpectedly due to loss of connection between the CE and the FE. 965 Therefore, the framework allows the bi-directional transition 966 between these two phases, but the ForCES protocol is only 967 applicable for the post-association phase. However, the protocol 968 should provide mechanisms to support association re-establishment. 969 This includes the ability for CEs and FEs to determine when there 970 is a loss of association between them, ability to restore 971 association and efficient state (re)synchronization mechanisms (see 972 [3] Section 5, requirement #7). Note that security association and 973 state must be also re-established to guarantee the same level of 974 security exists before and after the association re-establishment. 976 When an FE leaves or joins an existing NE that is already in post- 977 association phase, the CE needs to be aware of the impact on FE 978 topology and deals with the change accordingly. 980 4.3.1. CE graceful restart 982 The failure and restart of the CE in a router can potentially cause 983 much stress and disruption on the control plane throughout a 984 network. Because when a CE has to restart for any reason, the 985 router loses routing adjacencies or sessions with its routing 986 neighbors. Neighbors who detect the lost adjacency normally re- 987 compute new routes and then send routing updates to their own 988 neighbors to communicate the lost adjacency. Their neighbors do 989 the same thing to propagate throughout the network. In the 990 meantime, the restarting router cannot receive traffic from other 991 routers because the neighbors have stopped using the router's 992 previously advertised routes. When the restarting router restores 993 adjacencies, neighbors must once again re-compute new routes and 994 send out additional routing updates. The restarting router is 995 unable to forward packets until it has re-established routing 996 adjacencies with neighbors, received route updates through these 997 adjacencies, and computed new routes. Until convergence takes 998 place throughout the network, packets may be lost in transient 999 black holes or forwarding loops. 1001 A high availability mechanism known as the "graceful restart" has 1002 been used by the IP routing protocols (OSPF [10], BGP [11], BGP 1003 [11]) and MPLS label distribution protocol (LDP [9]) to help 1004 minimize the negative effects on routing throughout an entire 1005 network caused by a restarting router. Route flap on neighboring 1006 routers is avoided, and a restarting router can continue to forward 1007 packets that would otherwise be dropped. 1009 While the details differ from protocol to protocol, the general 1010 idea behind the graceful restart mechanism remains the same. With 1011 the graceful restart, a restarting router can inform its neighbors 1012 when it restarts. The neighbors may detect the lost adjacency but 1013 do not recompute new routes or send routing updates to their 1014 neighbors. The neighbors also hold on to the routes received from 1015 the restarting router before restart and assume they are still 1016 valid for a limited time. By doing so, the restarting router's FEs 1017 can also continue to receive and forward traffic from other 1018 neighbors for a limited time by using the routes they already have. 1019 The restarting router then re-establishes routing adjacencies, 1020 downloads updated routes from all its neighbors, recomputes new 1021 routes and uses them to replace the older routes it was using. It 1022 then sends these updated routes to its neighbors and signals the 1023 completion of the graceful restart process. 1025 Non-stop forwarding is a requirement for graceful restart. It is 1026 necessary so a router can continue to forward packets while it is 1027 downloading routing information and recomputing new routes. This 1028 ensures that packets will not be dropped. As one can see, one of 1029 the benefits afforded by the separation of CE and FE is exactly the 1030 ability of non-stop forwarding in the face of the CE failure and 1031 restart. The support of dynamic changes to CE/FE association in 1032 ForCES also makes it compatible with high availability mechanisms 1033 such as graceful restart. 1035 ForCES should be able to support CE graceful restart easily. When 1036 the association is established the first time, the CE must inform 1037 the FEs what to do in the case of CE failure. If graceful restart 1038 is not supported, the FEs may be told to stop packet processing all 1039 together if its CE fails. If graceful restart is supported, the 1040 FEs should be told to cache and hold on to its FE state including 1041 the forwarding tables across the restarts. A timer must be 1042 included so that the timeout causes such cached state to expire 1043 eventually. Those timers should be settable by the CE. 1045 4.3.2. FE restart 1047 In the same example in Figure 5, assuming CE1 is the working CE for 1048 the moment, what would happen if one of the FEs, say FE1, leaves 1049 the NE temporarily? FE1 may voluntarily decide to leave the 1050 association. Alternatively, FE1 may stop functioning simply due to 1051 unexpected failure. In former case, CE1 receives a "leave- 1052 association request" from FE1. In the latter, CE1 detects the 1053 failure of FE1 by some other means. In both cases, CE1 must inform 1054 the routing protocols of such an event, most likely prompting a 1055 reachability and SPF (Shortest Path First) recalculation and 1056 associated downloading of new FIBs from CE1 to the other remaining 1057 FEs (only FE2 in this example). Such recalculation and FIB update 1058 will also be propagated from the CE1 to its neighbors that are 1059 affected by the connectivity of FE1. 1061 When FE1 decides to rejoin again, or when it restarts again from 1062 the failure, FE1 needs to re-discover its master (CE). This can be 1063 achieved by several means. It may re-enter the pre-association 1064 phase and get that information from its FE manager. It may 1065 retrieve the previous CE information from its cache, if it can 1066 validate the information freshness. Once it discovers its CE, it 1067 starts message exchange with CE to re-establish the association 1068 just as outlined in Figure 9, with the possible exception that it 1069 might be able to bypass the transport of the complete initial 1070 configuration. Suppose that FE1 still has its routing table and 1071 other state information from the last association, instead of 1072 sending all the information again from scratch, it may be able to 1073 use more efficient mechanism to re-sync up the state with its CE if 1074 such mechanism is supported by the ForCES protocol. For example, 1075 CRC-32 of the state might give a quick indication of whether or not 1076 the state is in-sync with its CE. By comparing its state with CE 1077 first, it sends information update only if it is needed. ForCES 1078 protocol may choose to implement similar optimization mechanisms, 1079 but it may also choose not to, as this is not a requirement. 1081 5. Applicability to RFC1812 1083 [3] Section 5, requirement #9 dictates "Any proposed ForCES 1084 architecture must explain how that architecture supports all of the 1085 router functions as defined in RFC1812." RFC1812 discusses many 1086 important requirements for IPv4 routers from the link layer to the 1087 application layer. This section addresses the relevant 1088 requirements in RFC1812 for implementing IPv4 routers based on 1089 ForCES architecture and explains how ForCES satisfies these 1090 requirements by providing guidelines on how to separate the 1091 functionalities required into forwarding plane and control plane. 1093 In general, the forwarding plane carries out the bulk of the per- 1094 packet processing that is required at line speed, while the control 1095 plane carries most of the computationally complex operations that 1096 are typical of the control and signaling protocols. However, it is 1097 impossible to draw a rigid line to divide the processing into CEs 1098 and FEs cleanly. Nor should the ForCES architecture limit the 1099 innovative approaches in control and forwarding plane separation. 1100 As more and more processing power is available in the FEs, some of 1101 the control functions that traditionally are performed by CEs may 1102 now be moved to FEs for better performance and scalability. Such 1103 offloaded functions may include part of ICMP or TCP processing, or 1104 part of routing protocols. Once off-loaded onto the forwarding 1105 plane, such CE functions, even though logically belonging to the 1106 control plane, now become part of the FE functions. Just like the 1107 other logical functions performed by FEs, such off-loaded functions 1108 must be expressed as part of the FE model so that the CEs can 1109 decide how to best take advantage of these off-loaded functions 1110 when present on the FEs. 1112 5.1. General Router Requirements 1113 Routers have at least two or more logical interfaces. When CEs and 1114 FEs are separated by ForCES within a single NE, some additional 1115 interfaces are needed for intra-NE communications. Figure 12 shows 1116 an example to illustrate that. This NE contains one CE and two 1117 FEs. Each FE has four interfaces; two of them are used for 1118 receiving and transmitting packets to the external world, while the 1119 other two are for intra-NE connections. CE has two logical 1120 interfaces #9 and #10, connected to interfaces #3 and #6 from FE1 1121 and FE2, respectively. Interface #4 and #5 are connected for FE1- 1122 FE2 communication. Therefore, this router NE provides four 1123 external interfaces (#1, 2, 7 and 8). 1125 --------------------------------- 1126 | router NE | 1127 | ----------- ----------- | 1128 | | FE1 | | FE2 | | 1129 | ----------- ----------- | 1130 | 1| 2| 3| 4| 5| 6| 7| 8| | 1131 | | | | | | | | | | 1132 | | | | +----+ | | | | 1133 | | | | | | | | 1134 | | | 9| 10| | | | 1135 | | | -------------- | | | 1136 | | | | CE | | | | 1137 | | | -------------- | | | 1138 | | | | | | 1139 -----+--+----------------+--+---- 1140 | | | | 1141 | | | | 1143 Figure 12. A router NE example with four interfaces. 1145 IPv4 routers must implement IP to support its packet forwarding 1146 function, which is driven by its FIB (Forwarding Information Base). 1147 This Internet layer forwarding (see RFC1812 [1] Section 5) 1148 functionality naturally belongs to FEs in the ForCES architecture. 1150 A router may implement transport layer protocols (like TCP and UDP) 1151 that are required to support application layer protocols (see 1152 RFC1812 [1] Section 6). One important class of application 1153 protocols is routing protocols (see RFC1812 [1] Section 7). In 1154 ForCES architecture, routing protocols are naturally implemented by 1155 CEs. Routing protocols require routers communicate with each 1156 other. This communication between CEs in different routers is 1157 supported in ForCES by FEs' ability to redirect data packets 1158 addressed to routers (i.e., NEs) and CEs' ability to originate 1159 packets and have them delivered by their FEs. This communication 1160 occurs across Fp reference point inside each router and between 1161 neighboring routers' external interfaces, as illustrated in Figure 1162 11. 1164 5.2.Link Layer 1166 Since FEs own all the external interfaces for the router, FEs need 1167 to conform to the link layer requirements in RFC1812. Arguably, 1168 ARP support may be implemented in either CEs or FEs. As we will 1169 see later, a number of behaviors that RFC1812 mandates fall into 1170 this category -- they may be performed by the FE and may be 1171 performed by the CE. A general guideline is needed to ensure 1172 interoperability between separated control and forwarding planes. 1173 The guideline we offer here is that CEs MUST be capable of these 1174 kind of operations while FEs MAY choose to implement them. FE 1175 model should indicate its capabilities in this regard so that CEs 1176 can decide where these functions are implemented. 1178 Interface parameters, including MTU, IP address, etc., must be 1179 configurable by CEs via ForCES. CEs must be able to determine 1180 whether a physical interface in an FE is available to send packets 1181 or not. FEs must also inform CEs the status change of the 1182 interfaces (like link up/down) via ForCES. 1184 5.3.Internet Layer Protocols 1186 Both FEs and CEs must implement IP protocol and all mandatory 1187 extensions as RFC1812 specified. CEs should implement IP options 1188 like source route and record route while FEs may choose to 1189 implement those as well. The timestamp option should be 1190 implemented by FEs to insert the timestamp most accurately. The FE 1191 must interpret the IP options that it understands and preserve the 1192 rest unchanged for use by CEs. Both FEs and CEs might choose to 1193 silently discard packets without sending ICMP errors, but such 1194 events should be logged and counted. FEs may report statistics for 1195 such events to CEs via ForCES. 1197 When multiple FEs are involved to process packets, the appearance 1198 of single NE must be strictly maintained. For example, Time-To- 1199 Live (TTL) must be decremented only once within a single NE. For 1200 example, it can be always decremented by the last FE with egress 1201 function. 1203 FEs must receive and process normally any packets with a broadcast 1204 destination address or a multicast destination address that the 1205 router has asked to receive. When IP multicast is supported in 1206 routers, IGMP is implemented in CEs. CEs are also required of ICMP 1207 support, while it is optional for FEs to support ICMP. Such an 1208 option can be communicated to CEs as part of the FE model. 1209 Therefore, FEs can always rely upon CEs to send out ICMP error 1210 messages, but FEs also have the option to generate ICMP error 1211 messages themselves. 1213 5.4.Internet Layer Forwarding 1215 IP forwarding is implemented by FEs. When the routing table is 1216 updated at CEs, ForCES is used to send the new route entries from 1217 CEs to FEs. Each FE has its own forwarding table and uses this 1218 table to direct packets to the next hop interface. 1220 Upon receiving IP packets, the FE verifies the IP header and 1221 processes most of the IP options. Some options cannot be processed 1222 until the routing decision has been made. The routing decision is 1223 made after examining the destination IP address. If the 1224 destination address belongs to the router itself, the packets are 1225 filtered and either processed locally or forwarded to CE, depending 1226 upon the instructions set-up by CE. Otherwise, the FE determines 1227 the next hop IP address by looking up in its forwarding table. The 1228 FE also determines the network interface it uses to send the 1229 packets. Sometimes an FE may need to forward the packets to 1230 another FE before packets can be forwarded out to the next hop. 1231 Right before packets are forwarded out to the next hop, the FE 1232 decrements TTL by 1 and processes any IP options that cannot be 1233 processed before. The FE performs any IP fragmentation if 1234 necessary, determines link layer address (e.g., by ARP), and 1235 encapsulates the IP datagram (or each of the fragments thereof) in 1236 an appropriate link layer frame and queues it for output on the 1237 interface selected. 1239 Other options mentioned in RFC1812 for IP forwarding may also be 1240 implemented at FEs, for example, packet filtering. 1242 FEs typically forward packets destined locally to CEs. FEs may 1243 also forward exceptional packets (packets that FEs do not know how 1244 to handle) to CEs. CEs are required to handle packets forwarded by 1245 FEs for whatever different reasons. It might be necessary for 1246 ForCES to attach some meta-data with the packets to indicate the 1247 reasons of forwarding from FEs to CEs. Upon receiving packets with 1248 meta-data from FEs, CEs can decide to either process the packets 1249 themselves, or pass the packets to the upper layer protocols 1250 including routing and management protocols. If CEs are to process 1251 the packets by themselves, CEs may choose to discard the packets, 1252 or modify and re-send the packets. CEs may also originate new 1253 packets and deliver them to FEs for further forwarding. 1255 Any state change during router operation must also be handled 1256 correctly according to RFC1812. For example, when an FE ceases 1257 forwarding, the entire NE may continue forwarding packets, but it 1258 needs to stop advertising routes that are affected by the failed 1259 FE. 1261 5.5. Transport Layer 1263 Transport layer is typically implemented at CEs to support higher 1264 layer application protocols like routing protocols. In practice, 1265 this means that most CEs implement both the Transmission Control 1266 Protocol (TCP) and the User Datagram Protocol (UDP). 1268 Both CEs and FEs need to implement ForCES protocol. If some layer- 1269 4 transport is used to support ForCES, then both CEs and FEs need 1270 to implement the L4 transport and ForCES protocols. 1272 5.6. Application Layer -- Routing Protocols 1274 Interior and exterior routing protocols are implemented on CEs. 1275 The routing packets originated by CEs are forwarded to FEs for 1276 delivery. The results of such protocols (like forwarding table 1277 updates) are communicated to FEs via ForCES. 1279 For performance or scalability reasons, portions of the control 1280 plane functions that need faster response may be moved from the CEs 1281 and off-loaded onto the FEs. For example in OSPF, the Hello 1282 protocol packets are generated and processed periodically. When 1283 done at CEs, the inbound Hello packets have to traverse from the 1284 external interfaces at the FEs to the CEs via the internal CE-FE 1285 channel. Similarly, the outbound Hello packets have to go from the 1286 CEs to the FEs and to the external interfaces. Frequent Hello 1287 updates place heavy processing overhead on the CEs and can 1288 overwhelm the CE-FE channel as well. Since typically there are far 1289 more FEs than CEs in a router, the off-loaded Hello packets are 1290 processed in a much more distributed and scalable fashion. By 1291 expressing such off-loaded functions in the FE model, we can ensure 1292 interoperability. However, the exact description of the off-loaded 1293 functionality corresponding to the off-loaded functions expressed 1294 in the FE model are not part of the model itself and will need to 1295 be worked out as a separate specification. 1297 5.7. Application Layer -- Network Management Protocol 1299 RFC1812 also dictates "Routers MUST be manageable by SNMP." (see 1300 [4] Section 8) In general, for post-association phase, most 1301 external management tasks (including SNMP) should be done through 1302 interaction with the CE in order to support the appearance of a 1303 single functional device. Therefore, it is recommended that SNMP 1304 management agent be implemented by CEs and the SNMP messages 1305 received by FEs be redirected to their CEs. AgentX framework 1306 defined in RFC2741 ([5]) may be applied here such that CEs act in 1307 the role of master agent to process SNMP protocol messages while 1308 FEs act in the role of subagent to provide access to the MIB 1309 objects residing on FEs. AgentX protocol messages between the 1310 master agent (CE) and the subagent (FE) are encapsulated and 1311 transported via ForCES, just like data packets from any other 1312 application layer protocols. 1314 6. Summary 1316 This document defines an architectural framework for ForCES. It 1317 identifies the relevant components for a ForCES network element, 1318 including (one or more) FEs, (one or more) CEs, one optional FE 1319 manager, and one optional CE manager. It also identifies the 1320 interaction among these components and discusses all the major 1321 reference points. It is important to point out that, among all the 1322 reference points, only the Fp interface between CEs and FEs is 1323 within the scope of ForCES. ForCES alone may not be enough to 1324 support all desirable NE configurations. However, we believe that 1325 ForCES over Fp interface is the most important element in realizing 1326 physical separation and interoperability of CEs and FEs, and hence 1327 the first interface that ought to be standardized. Simple and 1328 useful configurations can still be implemented with only CE-FE 1329 interface being standardized, e.g., single CE with full-meshed FEs. 1331 7. Acknowledgements 1333 Joel M. Halpern gave us many insightful comments and suggestions 1334 and pointed out several major issues. T. Sridhar suggested that 1335 the AgentX protocol could be used with SNMP to manage the ForCES 1336 network elements. Many of our colleagues and people in the ForCES 1337 mailing list also provided valuable feedback. 1339 8. Security Considerations 1341 In general, the physical separation of two entities usually results 1342 in a potentially insecure link between the two entities and hence 1343 much stricter security measurements are required. For example, we 1344 pointed out in Section 4.1 that authentication becomes necessary 1345 between CE manager and FE manager, between CE and CE manager, 1346 between FE and FE manager in some configurations. The physical 1347 separation of CE and FE also imposes serious security requirement 1348 for ForCES protocol over Fp interface. This section first attempts 1349 to describe the security threats that may be introduced by the 1350 physical separation of the FEs and the CEs, and then it provides 1351 recommendation and guidelines for secure operation and management 1352 of ForCES protocol over Fp interface based on existing standard 1353 security solutions. 1355 8.1. Analysis of Potential Threats Introduced by ForCES 1357 This section provides the threat analysis for ForCES, with a focus 1358 on Fp interface. Each threat is described in details with the 1359 effects on the ForCES protocol entities or/and the NE as a whole, 1360 and the required functionalities that need to be in place to defend 1361 the threat. 1363 8.1.1. "Join" or "Remove" Message Flooding on CEs 1365 Threats: A malicious node could send a stream of false "join NE" 1366 or "remove from NE" requests on behalf of non-existent or 1367 unauthorized FE to legitimate CEs at a very rapid rate and thereby 1368 create unnecessary state in the CEs. 1370 Effects: If by maintaining state for non-existent or unauthorized 1371 FEs, a CE may become unavailable for other processing and hence 1372 suffer from denial of service (DoS) attack similar to the TCP SYN 1373 DoS. If multiple CEs are used, the unnecessary state information 1374 may also be conveyed to multiple CEs via Fr interface (e.g., from 1375 the active CE to the stand-by CE) and hence subject multiple CEs to 1376 DoS attack. 1378 Requirement: A CE that receives a "join" or "remove" request 1379 should not create any state information until it has authenticated 1380 the FE endpoint. 1382 8.1.2. Impersonation Attack 1384 Threats: A malicious node can impersonate a CE or FE and send out 1385 false messages. 1387 Effects: The whole NE could be compromised. 1389 Requirement: The CE or FE must authenticate the message before 1390 accepting and processing it. 1392 8.1.3. Replay Attack 1393 Threat: A malicious node could replay the entire message previously 1394 sent by an FE or CE entity to get around authentication. 1396 Effect: The NE could be compromised. 1398 Requirement: Replay protection mechanism needs to be part of the 1399 security solution to defend against this attack. 1401 8.1.4. Attack during Fail Over 1403 Threat: A malicious node may exploit the CE fail-over mechanism to 1404 take over the control of NE. For example, suppose two CEs, say CE-A 1405 and CE-B, are controlling several FEs. CE-A is active and CE-B is 1406 stand-by. When CE-A fails, CE-B is taking over the active CE 1407 position. The FEs already had a trusted relationship with CE-A, 1408 but the FEs may not have the same trusted relationship established 1409 with CE-B prior to the fail-over. A malicious node can take over 1410 as CE-B if such trusted relationship is not established during the 1411 fail-over. 1413 Effect: The NE may be compromised after such insecure fail-over. 1415 Requirement: The level of trust relationship between the stand-by 1416 CE and the FEs must be as strong as the one between the active CE 1417 and the FEs. The security association between the FEs and the 1418 stand-by CE may be established prior to fail-over. If not already 1419 in place, such security association must be re-established before 1420 the stand-by CE takes over. 1422 8.1.5. Data Integrity 1424 Threats: A malicious node may inject false messages to legitimate 1425 CE or FE. 1427 Effect: An FE or CE receives the fabricated packet and performs 1428 incorrect or catastrophic operation. 1430 Requirement: Protocol messages require integrity protection. 1432 8.1.6. Data Confidentiality 1434 Threat: When FE and CE are physically separated, a malicious node 1435 may eavesdrop the messages in transit. Some of the messages are 1436 critical to the functioning of the whole network, while others may 1437 contain confidential business data. Leaking of such information 1438 may result in compromise even beyond the immediate CE or FE. 1440 Effect: Sensitive information might be exposed between CE and FE. 1442 Requirement: Data confidentiality between FE and CE must be 1443 available for sensitive information. 1445 8.1.7. Sharing security parameters 1447 Threat: Consider a scenario where several FEs communicating to the 1448 same CE share the same authentication keys for the Fp interface. 1449 If any FE or the CE is compromised, all other entities are 1450 compromised. 1452 Effect: The whole NE is compromised. 1454 Recommendation: To avoid this side effect, it's better to configure 1455 different security parameters for each FE-CE communication over Fp 1456 interface. 1458 8.1.8. Denial of Service Attack via External Interface 1460 Threat: When an FE receives a packet that is destined for its CE, 1461 the FE forwards the packet over the Fp interface. Malicious node 1462 can generate huge message storm like routing protocol packets etc. 1463 through the external Fi/f interface so that the FE has to process 1464 and forward all packets to CE through Fp interface. 1466 Effect: CE encounters resource exhaustion and bandwidth starvation 1467 on Fp interface due to an overwhelming number of packets from FEs. 1469 Requirement: Some sort of rate limiting mechanism MUST to be in 1470 place at both FE and CE. Examples of such mechanisms include 1471 explicit rate limiters or congestion control algorithms. Rate 1472 Limiter SHOULD be configured at FE for each message type that are 1473 being received through Fi/F interface. 1475 8.2. Security Recommendations for ForCES 1477 The requirements document [3] suggested that ForCES protocol should 1478 support reliability over Fp interface, but no particular transport 1479 protocol is yet specified for ForCES. This framework document does 1480 not intend to specify the particular transport either, and so we 1481 only provide recommendations and guidelines based on the existing 1482 standard security protocols that can work with the common transport 1483 candidates suitable for ForCES. 1485 We review two existing security protocol solutions, namely IPsec 1486 (IP Security) [14] or TLS (Transport Layer Security) [13]. TLS 1487 works with reliable transports such as TCP or SCTP for unicast, 1488 while IPsec can be used with any transport (UDP, TCP, SCTP) and 1489 supports both unicast and multicast. Both TLS and IPsec can be 1490 used potentially to satisfy all of the security requirements for 1491 ForCES protocol. Other approaches may be used as well but are not 1492 documented here. 1494 When ForCES is deployed between CEs and FEs inside a box, 1495 authentication, confidentiality and integrity may be provided by 1496 the physical security of the box and so the security mechanisms may 1497 be turned off, depending on the networking topology and its 1498 administration policy. However, it is important to realize that 1499 even if the NE is in a single-box, the DoS attacks as described in 1500 Section 8.1.8 can still be launched through Fi/f interfaces. 1501 Therefore, it is important to have the corresponding counter- 1502 measurement in place even for single-box deployment. 1504 8.2.1. Security Configuration 1506 The NE administrator has the freedom to determine the exact 1507 security configuration that is needed for the specific deployment. 1508 For example, ForCES may be deployed between CEs and FEs connected 1509 to each other inside a box over a backplane. In such scenario, 1510 physical security of the box ensures that most of the attacks such 1511 as man-in-the-middle, snooping, and impersonation are not possible, 1512 and hence ForCES architecture may rely on the physical security of 1513 the box to defend against these attacks and protocol mechanisms may 1514 be turned off. However, it is also shown that denial of service 1515 attack via external interface as described in Section 8.1.8 is 1516 still a potential threat even for such "all-in-one-box" deployment 1517 scenario and hence the rate limiting mechanism is still necessary. 1518 This is just one example to show that it is important to assess the 1519 security needs of the ForCES-enabled network elements under 1520 different deployment scenarios. It should be possible for the 1521 administrator to configure the level of security needed for the 1522 ForCES protocol. 1524 8.2.2. Using TLS with ForCES 1526 TLS [13] can be used if a reliable unicast transport such as TCP or 1527 SCTP is used for ForCES over the Fp interface. The TLS handshake 1528 protocol is used during association establishment or re- 1529 establishment phase to negotiate a TLS session between the CE and 1530 FE. Once the session is in place, the TLS record protocol is used 1531 to secure ForCES communication messages between the CE and FE. 1533 A basic outline of how TLS can be used with ForCES is described 1534 below. Steps 1) till 7) complete the security handshake as 1535 illustrated in Figure 9 while step 8) is for all the further 1536 communication between the CE and FE, including the rest of messages 1537 after the security handshake shown in Figure 9 and the steady-state 1538 communication shown in Figure 10. 1540 1) During Pre-association phase all FEs are configured with 1541 the CEs (including both the active CE and the standby CE). 1542 2) The FE establishes a TLS connection with the CE (master) 1543 and negotiates a cipher suite. 1544 3) The FE (slave) gets the CE certificate, validates the 1545 signature, checks the expiration date, checks if the 1546 certificate has been revoked. 1547 4) The CE (master) gets the FE certificate and performs the 1548 same validation as the FE in step 3). 1549 5) If any of the check fails in step 3) or step 4), endpoint 1550 must generate an error message and abort. 1551 6) After successful mutual authentication, a TLS session is 1552 established between CE and FE. 1553 7) The FE sends a "join NE" message to the CE. 1554 8) The FE and CE use TLS session for further communication. 1556 Note that there are different ways for the CE and FE to validate a 1557 received certificate. One way is to configure the FE Manager or CE 1558 Manager or other central component as CA, so that the CE or FE can 1559 query this pre-configured CA to validate that the certificate has 1560 not been revoked. Another way is to have the CE and the FE 1561 configured directly a list of valid certificates in the pre- 1562 association phase. 1564 In the case of fail-over, it is the responsibility of the active CE 1565 and the standby CE to synchronize ForCES states including the TLS 1566 states to minimize the state reestablishment during fail-over. 1567 Care must be taken to ensure that the standby CE is also 1568 authenticated in the same way as the active CE, either before or 1569 during the fail-over. 1571 8.2.3. Using IPsec with ForCES 1573 IPsec [14] can be used with any transport protocol, such as UDP, 1574 SCTP and TCP over Fp interface for ForCES. When using IPsec, we 1575 recommend using ESP in transport mode for ForCES because message 1576 confidentiality is required for ForCES. 1578 IPsec can be used with both manual and automated SA and 1579 cryptographic key management. But Ipsec's replay protection 1580 mechanisms are not available if manual key management is used. 1581 Hence, automatic key management is recommended if replay protection 1582 is deemed important. Otherwise, manual key management might be 1583 sufficient for some deployment scenarios, esp. when the number of 1584 CEs and FEs is relatively small. It is recommended that the keys 1585 be changed periodically even for manual key management. 1587 IPsec can support both unicast and multicast transport. At the time 1588 this document was published, MSEC working group is actively working 1589 on standardizing protocols to provide multicast security [17]. 1590 Multicast-based solutions relying on IPsec should specify how to 1591 meet the security requirements in [3]. 1593 Unlike TLS, IPsec provides security services between the CE and FE 1594 at IP level, and so the security handshake as illustrated in Figure 1595 9 amounts to a "no-op" when manual key management is used. The 1596 following outline the steps taken for ForCES in such a case. 1598 1) During Pre-association phase all FEs are configured with 1599 the CEs (including active CE and standby CE) and SA parameters 1600 manually. 1601 2) The FE sends a "join NE" message to the CE. This message 1602 and all others that follow are afforded security service 1603 according to the manually configured IPsec SA parameters, but 1604 replay protection is not available. 1606 It is up to the administrator to decide whether to share the same 1607 key across multiple FE-CE communication, but it is recommended that 1608 different keys be used. Similarly, it is recommended that 1609 different keys be used for inbound and outbound traffic. 1611 If automatic key management is needed, IKE [15] can be used for 1612 that purpose. Other automatic key distribution techniques such as 1613 Kerberos may be used as well. The key exchange process 1614 constitutes the security handshake as illustrated in Figure 9. The 1615 following shows the steps involved in using IKE with IPsec for 1616 ForCES. Steps 1) to 6) constitute the security handshake in Figure 1617 9. 1619 1) During Pre-association phase all FEs are configured with 1620 the CEs (including active CE and standby CE), IPsec policy 1621 etc. 1622 2) The FE kicks off IKE process and tries to establish an 1623 IPsec SA with the CE (master). The FE (Slave) gets the CE 1624 certificate as part of the IKE negotiation. The FE validates 1625 signature, checks the expiration date, checks if the 1626 certificate has been revoked. 1627 3) The CE (master) gets the FE certificate and performs the 1628 same check as the FE in step 2). 1629 4) If any of the check fails in step 2) or step 3), the 1630 endpoint must generate an error message and abort. 1631 5) After successful mutual authentication, IPsec session is 1632 established between the CE and FE. 1633 6) The FE sends a "join NE" message to CE. No SADB entry is 1634 created in FE yet. 1635 7) The FE and CE use the IPsec session for further 1636 communication. 1638 FE Manager or CE Manager or other central component can be used as 1639 CA for validating CE and FE certificates during the IKE process. 1640 Alternatively, during the pre-association phase, the CE and FE can 1641 be configured directly with the required information such as 1642 certificates or passwords etc depending upon the type of 1643 authentication that administrator wants to configure. 1645 In the case of fail-over, it is the responsibility of active CE and 1646 standby CE to synchronize ForCES states and IPsec states to 1647 minimize the state reestablishment during fail-over. 1648 Alternatively, the FE needs to establish different IPsec SA during 1649 the startup operation itself with each CE. This will minimize the 1650 periodic state transfer across IPsec layer though Fr (CE-CE) 1651 Interface. 1653 9. Normative References 1655 [1] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, 1656 June 1995. 1658 [2] Floyd, S., "Congestion Control Principles", RFC 2914, September 1659 2000. 1661 [3] Khosravi, H. et al., "Requirements for Separation of IP Control 1662 and Forwarding", work in progress, May 2003, . 1665 10. Informative References 1667 [4] Case, J., et al., "A Simple Network Management Protocol 1668 (SNMP)", RFC 1157, May 1990. 1670 [5] Daniele, M. et al., "Agent Extensibility (AgentX) Protocol 1671 Version 1", RFC 2741, January 2000. 1673 [6] Chan, K. et al., "COPS Usage for Policy Provisioning (COPS- 1674 PR)", RFC 3084, March 2001. 1676 [7] Crouch, A. et al., "ForCES Applicability Statement", work in 1677 progress, June 2002, . 1679 [8] Anderson, T. and J. Buerkle, "Requirements for the Dynamic 1680 Partitioning of Switching Elements", RFC 3532, May 2003. 1682 [9] Leelanivas, M. et al., "Graceful Restart Mechanism for Label 1683 Distribution Protocol", RFC 3478, February 2003. 1685 [10] Moy, J. et al., "Graceful OSPF Restart", work in progress, 1686 March 2003, . 1688 [11] Sangli, S. et al., "Graceful Restart Mechanism for BGP", work 1689 in progress, January 2003, < draft-ietf-idr-restart-06.txt>. 1691 [12] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", work 1692 in progress, March 2003, . 1694 [13] Dierks, T. and C. Allen, "The TLS Protocol, version 1.0", RFC 1695 2246, January 1999. 1697 [14] Kent, S. and R. Atkinson, "Security Architecture for the 1698 Internet Protocol", RFC 2401, November 1998. 1700 [15] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE) ", 1701 RFC 2409, November 1998. 1703 [16] Bellovin, S., "Guidelines for Mandating the Use of Ipsec", 1704 work in progress, October 2002, . 1706 [17] Hardjono, T. and Weis, B. "The Multicast Security 1707 Architecture", work in progress, August 2003, . 1710 11. Authors' Addresses 1712 L. Lily Yang 1713 Intel Corp., MS JF3-206, 1714 2111 NE 25th Avenue 1715 Hillsboro, OR 97124, USA 1716 Phone: +1 503 264 8813 1717 Email: lily.l.yang@intel.com 1718 Ram Dantu 1719 Department of Computer Science, 1720 University of North Texas, 1721 Denton, TX 76203, USA 1722 Phone: +1 940 565 2822 1723 Email: rdantu@unt.edu 1725 Todd A. Anderson 1726 Intel Corp. 1727 2111 NE 25th Avenue 1728 Hillsboro, OR 97124, USA 1729 Phone: +1 503 712 1760 1730 Email: todd.a.anderson@intel.com 1732 Ram Gopal 1733 Nokia Research Center 1734 5, Wayside Road, 1735 Burlington, MA 01803, USA 1736 Phone: +1 781 993 3685 1737 Email: ram.gopal@nokia.com 1739 12. 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