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'14') (Obsoleted by RFC 4301) -- Obsolete informational reference (is this intentional?): RFC 2409 (ref. '15') (Obsoleted by RFC 4306) Summary: 4 errors (**), 0 flaws (~~), 9 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Draft L. Yang 2 Expiration: February 2004 Intel Corp. 3 File: draft-ietf-forces-framework-08.txt R. Dantu 4 Working Group: ForCES Univ. of North Texas 5 T. Anderson 6 Intel Corp. 7 R. Gopal 8 Nokia 9 August 2003 11 Forwarding and Control Element Separation (ForCES) Framework 13 draft-ietf-forces-framework-08.txt 15 Status of this Memo 17 This document is an Internet-Draft and is in full conformance with 18 all provisions of Section 10 of RFC2026. Internet-Drafts are 19 working documents of the Internet Engineering Task Force (IETF), 20 its areas, and its working groups. Note that other groups may also 21 distribute working documents as Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other 25 documents at any time. It is inappropriate to use Internet-Drafts 26 as reference material or to cite them other than as ``work in 27 progress.'' 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Copyright Notice 37 Copyright (C) The Internet Society (2003). All Rights Reserved. 39 Abstract 41 This document defines the architectural framework for the ForCES 42 (Forwarding and Control Element Separation) network elements, and 43 identifies the associated entities and the interaction among them. 45 Table of Contents 46 1. Definitions...................................................3 47 2. Introduction to Forwarding and Control Element Separation 48 (ForCES).........................................................5 49 3. Architecture..................................................9 50 3.1. Control Elements and Fr Reference Point.................10 51 3.2. Forwarding Elements and Fi reference point..............11 52 3.3. CE Managers.............................................14 53 3.4. FE Managers.............................................14 54 4. Operational Phases...........................................15 55 4.1. Pre-association Phase...................................15 56 4.1.1. Fl Reference Point.................................15 57 4.1.2. Ff Reference Point.................................16 58 4.1.3. Fc Reference Point.................................17 59 4.2. Post-association Phase and Fp reference point...........17 60 4.2.1. Proximity and Interconnect between CEs and FEs.....17 61 4.2.2. Association Establishment..........................18 62 4.2.3. Steady-state Communication.........................19 63 4.2.4. Data Packets across Fp reference point.............20 64 4.2.5. Proxy FE...........................................21 65 4.3. Association Re-establishment............................21 66 4.3.1. CE graceful restart................................21 67 4.3.2. FE restart.........................................23 68 5. Applicability to RFC1812.....................................24 69 5.1. General Router Requirements.............................24 70 5.2. Link Layer..............................................25 71 5.3. Internet Layer Protocols................................26 72 5.4. Internet Layer Forwarding...............................26 73 5.5. Transport Layer.........................................27 74 5.6. Application Layer -- Routing Protocols..................28 75 5.7. Application Layer -- Network Management Protocol........28 76 6. Summary......................................................29 77 7. Security Considerations......................................29 78 7.1. Analysis of Potential Threats Introduced by ForCES......29 79 7.1.1. "Join" or "Remove" Message Flooding on CEs.........29 80 7.1.2. Impersonation Attack...............................30 81 7.1.3. Replay Attack......................................30 82 7.1.4. Attack during Fail Over............................30 83 7.1.5. Data Integrity.....................................31 84 7.1.6. Data Confidentiality...............................31 85 7.1.7. Sharing security parameters........................31 86 7.1.8. Denial of Service Attack via External Interface....32 87 7.2. Security Recommendations for ForCES.....................32 88 7.2.1. Security Configuration.............................33 89 7.2.2. Using TLS with ForCES..............................33 90 7.2.3. Using IPsec with ForCES............................34 91 8. Normative References.........................................36 92 9. Informative References.......................................36 93 10. Acknowledgements............................................37 94 11. Authors' Addresses..........................................37 95 12. Intellectual Property Right.................................38 96 13. Full Copyright Statement....................................38 98 Conventions used in this document 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 102 this document are to be interpreted as described in [RFC-2119]. 104 1. Definitions 106 A set of terminology associated with the ForCES requirements is 107 defined in [3] and we only include the definitions that are most 108 relevant to this document here. 110 Addressable Entity (AE) - An entity that is directly addressable 111 given some interconnect technology. For example, on IP networks, 112 it is a device to which we can communicate using an IP address; on 113 a switch fabric, it is a device to which we can communicate using a 114 switch fabric port number. 116 Physical Forwarding Element (PFE) - An AE that includes hardware 117 used to provide per-packet processing and handling. This hardware 118 may consist of (but is not limited to) network processors, ASICs 119 (Application-Specific Integrated Circuits), or general processors, 120 installed on line cards, daughter boards, mezzanine cards, or in 121 stand-alone boxes. 123 PFE Partition - A logical partition of a PFE consisting of some 124 subset of each of the resources (e.g., ports, memory, forwarding 125 table entries) available on the PFE. This concept is analogous to 126 that of the resources assigned to a virtual switching element as 127 described in [8]. 129 Physical Control Element (PCE) - An AE that includes hardware used 130 to provide control functionality. This hardware typically includes 131 a general-purpose processor. 133 PCE Partition - A logical partition of a PCE consisting of some 134 subset of each of the resources available on the PCE. 136 Forwarding Element (FE) - A logical entity that implements the 137 ForCES protocol. FEs use the underlying hardware to provide per- 138 packet processing and handling as directed by a CE via the ForCES 139 protocol. FEs may happen to be a single blade (or PFE), a 140 partition of a PFE or multiple PFEs. 142 Control Element (CE) - A logical entity that implements the ForCES 143 protocol and uses it to instruct one or more FEs how to process 144 packets. CEs handle functionality such as the execution of control 145 and signaling protocols. CEs may consist of PCE partitions or 146 whole PCEs. 148 ForCES Network Element (NE) - An entity composed of one or more CEs 149 and one or more FEs. To entities outside an NE, the NE represents 150 a single point of management. Similarly, an NE usually hides its 151 internal organization from external entities. 153 Pre-association Phase - The period of time during which an FE 154 Manager (see below) and a CE Manager (see below) are determining 155 which FE and CE should be part of the same network element. 157 Post-association Phase - The period of time during which an FE does 158 know which CE is to control it and vice versa, including the time 159 during which the CE and FE are establishing communication with one 160 another. 162 ForCES Protocol - While there may be multiple protocols used within 163 the overall ForCES architecture, the term "ForCES protocol" refers 164 only to the ForCES post-association phase protocol (see below). 166 ForCES Post-Association Phase Protocol - The protocol used for 167 post-association phase communication between CEs and FEs. This 168 protocol does not apply to CE-to-CE communication, FE-to-FE 169 communication, nor to communication between FE and CE managers. 170 The ForCES protocol is a master-slave protocol in which FEs are 171 slaves and CEs are masters. This protocol includes both the 172 management of the communication channel (e.g., connection 173 establishment, heartbeats) and the control messages themselves. 174 This protocol could be a single protocol or could consist of 175 multiple protocols working together. 177 FE Manager - A logical entity that operates in the pre-association 178 phase and is responsible for determining to which CE(s) an FE 179 should communicate. This process is called CE discovery and may 180 involve the FE manager learning the capabilities of available CEs. 181 A FE manager may use anything from a static configuration to a pre- 182 association phase protocol (see below) to determine which CE(s) to 183 use, however this is currently out of scope. Being a logical 184 entity, an FE manager might be physically combined with any of the 185 other logical entities mentioned in this section. 187 CE Manager - A logical entity that operates in the pre-association 188 phase and is responsible for determining to which FE(s) a CE should 189 communicate. This process is called FE discovery and may involve 190 the CE manager learning the capabilities of available FEs. A CE 191 manager may use anything from a static configuration to a pre- 192 association phase protocol (see below) to determine which FE to 193 use, however this is currently out of scope. Being a logical 194 entity, a CE manager might be physically combined with any of the 195 other logical entities mentioned in this section. 197 Pre-association Phase Protocol - A protocol between FE managers and 198 CE managers that is used to determine which CEs or FEs to use. A 199 pre-association phase protocol may include a CE and/or FE 200 capability discovery mechanism. Note that this capability 201 discovery process is wholly separate from (and does not replace) 202 that used within the ForCES protocol. However, the two capability 203 discovery mechanisms may utilize the same FE model. 205 FE Model - A model that describes the logical processing functions 206 of an FE. 208 ForCES Protocol Element - An FE or CE. 210 Intra-FE topology - Representation of how a single FE is realized 211 by combining possibly multiple logical functional blocks along 212 multiple data path. This is defined by the FE model. 214 FE Topology -- Representation of how the multiple FEs in a single 215 NE are interconnected. Sometimes it is called inter-FE topology, 216 to be distinguished from intra-FE topology used by the FE model. 218 Inter-FE topology - see FE Topology. 220 2. Introduction to Forwarding and Control Element Separation (ForCES) 222 An IP network element (NE) appears to external entities as a 223 monolithic piece of network equipment, e.g., a router, NAT, 224 firewall, or load balancer. Internally, however, an IP network 225 element (NE) (such as a router) is composed of numerous logically 226 separated entities that cooperate to provide a given functionality 227 (such as routing). Two types of network element components exist: 228 control element (CE) in control plane and forwarding element (FE) 229 in forwarding plane (or data plane). Forwarding elements typically 230 are ASIC, network-processor, or general-purpose processor-based 231 devices that handle data path operations for each packet. Control 232 elements are typically based on general-purpose processors that 233 provide control functionality like routing and signaling protocols. 235 ForCES aims to define a framework and associated protocol(s) to 236 standardize information exchange between the control and forwarding 237 plane. Having standard mechanisms allows CEs and FEs to become 238 physically separated standard components. This physical separation 239 accrues several benefits to the ForCES architecture. Separate 240 components would allow component vendors to specialize in one 241 component without having to become experts in all components. 242 Standard protocol also allows the CEs and FEs from different 243 component vendors to interoperate with each other and hence it 244 becomes possible for system vendors to integrate together the CEs 245 and FEs from different component suppliers. This interoperability 246 translates into a lot more design choices and flexibility for the 247 system vendors. Overall, ForCES will enable rapid innovation in 248 both the control and forwarding planes while maintaining 249 interoperability. Scalability is also easily provided by this 250 architecture in that additional forwarding or control capacity can 251 be added to existing network elements without the need for forklift 252 upgrades. 254 ------------------------- ------------------------- 255 | Control Blade A | | Control Blade B | 256 | (CE) | | (CE) | 257 ------------------------- ------------------------- 258 ^ | ^ | 259 | | | | 260 | V | V 261 --------------------------------------------------------- 262 | Switch Fabric Backplane | 263 --------------------------------------------------------- 264 ^ | ^ | ^ | 265 | | | | . . . | | 266 | V | V | V 267 ------------ ------------ ------------ 268 |Router | |Router | |Router | 269 |Blade #1 | |Blade #2 | |Blade #N | 270 | (FE) | | (FE) | | (FE) | 271 ------------ ------------ ------------ 272 ^ | ^ | ^ | 273 | | | | . . . | | 274 | V | V | V 276 Figure 1. A router configuration example with separate blades. 278 One example of such physical separation is at the blade level. 279 Figure 1 shows such an example configuration of a router, with two 280 control blades and multiple router (forwarding) blades, all 281 interconnected into a switch fabric backplane. In such a chassis 282 configuration, the control blades are the CEs while the router 283 blades are FEs, and the switch fabric backplane provides the 284 physical interconnect for all the blades. Control blade A may be 285 the primary CE while control blade B may be the backup CE providing 286 redundancy. It is also possible to have a redundant switch fabric 287 for high availability support. Routers today with this kind of 288 configuration use proprietary interfaces for messaging between CEs 289 and FEs. The goal of ForCES is to replace such proprietary 290 interfaces with a standard protocol. With a standard protocol like 291 ForCES implemented on all blades, it becomes possible for control 292 blades from vendor X and routing blades from vendor Y to work 293 seamlessly together in one chassis. 295 ------- ------- 296 | CE1 | | CE2 | 297 ------- ------- 298 ^ ^ 299 | | 300 V V 301 ============================================ Ethernet 302 ^ ^ . . . ^ 303 | | | 304 V V V 305 ------- ------- -------- 306 | FE#1| | FE#2| | FE#n | 307 ------- ------- -------- 308 ^ | ^ | ^ | 309 | | | | | | 310 | V | V | V 312 Figure 2. A router configuration example with separate boxes. 314 Another level of physical separation between the CEs and FEs can be 315 at the box level. In such configuration, all the CEs and FEs are 316 physically separated boxes, interconnected with some kind of high 317 speed LAN connection (like Gigabit Ethernet). These separated CEs 318 and FEs are only one hop away from each other within a local area 319 network. The CEs and FEs communicate to each other by running 320 ForCES, and the collection of these CEs and FEs together become one 321 routing unit to the external world. Figure 2 shows such an example. 323 In both examples shown here, the same physical interconnect is used 324 for both CE-to-FE and FE-to-FE communication. However, that does 325 not have to be the case. One reason to use different interconnects 326 is that CE-to-FE interconnect does not have to be as fast as the 327 FE-to-FE interconnect, so the more expensive fast connections can 328 be saved for FE-to-FE. The separate interconnects may also provide 329 reliability and redundancy benefits for the NE. 331 Some examples of control functions that can be implemented in the 332 CE include routing protocols like RIP, OSPF and BGP, control and 333 signaling protocols like RSVP (Resource Reservation Protocol), LDP 334 (Label Distribution Protocol) for MPLS, etc. Examples of 335 forwarding functions in the FE include LPM (longest prefix match) 336 forwarder, classifiers, traffic shaper, meter, NAT (Network Address 337 Translators), etc. Figure 3 provides example functions in both CE 338 and FE. Any given NE may contain one or many of these CE and FE 339 functions in it. The diagram also shows that ForCES protocol is 340 used to transport both the control messages for ForCES itself and 341 the data packets that are originated/destined from/to the control 342 functions in CE (e.g., routing packets). Section 4.2.4 provides 343 more detail on this. 345 ------------------------------------------------- 346 | | | | | | | 347 |OSPF |RIP |BGP |RSVP |LDP |. . . | 348 | | | | | | | 349 ------------------------------------------------- 350 | ForCES Interface | 351 ------------------------------------------------- 352 ^ ^ 353 ForCES | |data 354 control | |packets 355 messages| |(e.g., routing packets) 356 v v 357 ------------------------------------------------- 358 | ForCES Interface | 359 ------------------------------------------------- 360 | | | | | | | 361 |LPM Fwd|Meter |Shaper |NAT |Classi-|. . . | 362 | | | | |fier | | 363 ------------------------------------------------- 364 | FE resources | 365 ------------------------------------------------- 367 Figure 3. Examples of CE and FE functions 369 A set of requirements for control and forwarding separation is 370 identified in [3]. This document describes a ForCES architecture 371 that satisfies the architectural requirements of that document and 372 defines a framework for ForCES network elements and the associated 373 entities to facilitate protocol definition. Whenever necessary, 374 this document uses many examples to illustrate the issues and/or 375 possible solutions in ForCES. These examples are intended to be 376 just examples, and should not be taken as the only or definite ways 377 of doing certain things. It is expected that separate document 378 will be produced by the ForCES working group to specify the ForCES 379 protocol(s). 381 3. Architecture 383 This section defines the ForCES architectural framework and the 384 associated logical components. This ForCES framework defines 385 components of ForCES NEs including several ancillary components. 386 These components may be connected in different kinds of topologies 387 for flexible packet processing. 389 --------------------------------------- 390 | ForCES Network Element | 391 -------------- Fc | -------------- -------------- | 392 | CE Manager |---------+-| CE 1 |------| CE 2 | | 393 -------------- | | | Fr | | | 394 | | -------------- -------------- | 395 | Fl | | | Fp / | 396 | | Fp| |----------| / | 397 | | | |/ | 398 | | | | | 399 | | | Fp /|----| | 400 | | | /--------/ | | 401 -------------- Ff | -------------- -------------- | 402 | FE Manager |---------+-| FE 1 | Fi | FE 2 | | 403 -------------- | | |------| | | 404 | -------------- -------------- | 405 | | | | | | | | | | 406 ----+--+--+--+----------+--+--+--+----- 407 | | | | | | | | 408 | | | | | | | | 409 Fi/f Fi/f 411 Figure 4. ForCES Architectural Diagram 413 The diagram in Figure 4 shows the logical components of the ForCES 414 architecture and their relationships. There are two kinds of 415 components inside a ForCES network element: control element (CE) 416 and forwarding element (FE). The framework allows multiple 417 instances of CE and FE inside one NE. Each FE contains one or 418 more physical media interfaces for receiving and transmitting 419 packets from/to the external world. The aggregation of these FE 420 interfaces becomes the NE's external interfaces. In addition to 421 the external interfaces, there must also exist some kind of 422 interconnect within the NE so that the CE and FE can communicate 423 with each other, and one FE can forward packets to another FE. 424 The diagram also shows two entities outside of the ForCES NE: CE 425 Manager and FE Manager. These two entities provide configuration 426 to the corresponding CE or FE in the pre-association phase (see 427 Section 5.1). There is no defined role for FE Manager and CE 428 Manager in post-association phase, thus these logical components 429 are not considered part of the ForCES NE. 431 For convenience, the logical interactions between these components 432 are labeled by reference points Fp, Fc, Ff, Fr, Fl, and Fi, as 433 shown in Figure 4. The FE external interfaces are labeled as Fi/f. 434 More detail is provided in Section 4 and 5 for each of these 435 reference points. All these reference points are important in 436 understanding the ForCES architecture, however, the ForCES protocol 437 is only defined over one reference point -- Fp. 439 The interface between two ForCES NEs is identical to the interface 440 between two conventional routers and these two NEs exchange the 441 protocol packets through the external interfaces at Fi/f. ForCES 442 NEs connect to existing routers transparently. 444 3.1. Control Elements and Fr Reference Point 446 It is not necessary to define any protocols across the Fr reference 447 point to enable control and forwarding separation for simple 448 configurations like single CE and multiple FEs. However, this 449 architecture permits multiple CEs to be present in a network 450 element. In cases where an implementation uses multiple CEs, the 451 invariant that the CEs and FEs together appear as a single NE must 452 be maintained. 454 Multiple CEs may be used for redundancy, load sharing, distributed 455 control, or other purposes. Redundancy is the case where one or 456 more CEs are prepared to take over should an active CE fail. Load 457 sharing is the case where two or more CEs are concurrently active 458 and any request that can be serviced by one of the CEs can also be 459 serviced by any of the other CEs. For both redundancy and load 460 sharing, the CEs involved are equivalently capable. The only 461 difference between these two cases is in terms of how many active 462 CEs there are. Distributed control is the case where two or more 463 CEs are concurrently active but certain requests can only be 464 serviced by certain CEs. 466 When multiple CEs are employed in a ForCES NE, their internal 467 organization is considered an implementation issue that is beyond 468 the scope of ForCES. CEs are wholly responsible for coordinating 469 amongst themselves via the Fr reference point to provide 470 consistency and synchronization. However, ForCES does not define 471 the implementation or protocols used between CEs, nor does it 472 define how to distribute functionality among CEs. Nevertheless, 473 ForCES will support mechanisms for CE redundancy or fail over, and 474 it is expected that vendors will provide redundancy or fail over 475 solutions within this framework. 477 3.2. Forwarding Elements and Fi reference point 479 An FE is a logical entity that implements the ForCES protocol and 480 uses the underlying hardware to provide per-packet processing and 481 handling as directed by a CE. It is possible to partition one 482 physical FE into multiple logical FEs. It is also possible for one 483 FE to use multiple physical FEs. The mapping between physical 484 FE(s) and the logical FE(s) is beyond the scope of ForCES. For 485 example, a logical partition of a physical FE can be created by 486 assigning some portion of each of the resources (e.g., ports, 487 memory, forwarding table entries) available on the physical FE to 488 each of the logical FEs. Such concept of FE virtualization is 489 analogous to a virtual switching element as described in [8]. FE 490 virtualization should occur only in the pre-association phase and 491 hence has no impact on ForCES. 493 FEs perform all packet processing functions as directed by CEs. 494 FEs have no initiative of their own. Instead, FEs are slaves and 495 only do as they are told. FEs may communicate with one or more CEs 496 concurrently across reference point Fp. FEs have no notion of CE 497 redundancy, load sharing, or distributed control. Instead, FEs 498 accept commands from any CE authorized to control them, and it is 499 up to the CEs to coordinate among themselves to achieve redundancy, 500 load sharing or distributed control. The idea is to keep FEs as 501 simple and dumb as possible so that FEs can focus their resource on 502 the packet processing functions. 504 For example, in Figure 5, FE1 and FE2 can be configured to accept 505 commands from both the primary CE (CE1) and the backup CE (CE2). 506 Upon detection of CE1 failure, perhaps across the Fr or Fp 507 reference point, CE2 is configured to take over activities of CE1. 508 This is beyond the scope of ForCES and is not discussed further. 510 Distributed control can be achieved in the similar fashion, without 511 much intelligence on the part of FEs. For example, FEs can be 512 configured to detect RSVP and BGP protocol packets, and forward 513 RSVP packets to one CE and BGP packets to another CE. Hence, FEs 514 may need to do packet filtering for forwarding packets to specific 515 CEs. 517 ------- Fr ------- 518 | CE1 | ------| CE2 | 519 ------- ------- 520 | \ / | 521 | \ / | 522 | \ / | 523 | \/Fp | 524 | /\ | 525 | / \ | 526 | / \ | 527 ------- Fi ------- 528 | FE1 |<----->| FE2 | 529 ------- ------- 531 Figure 5. CE redundancy example. 533 This architecture permits multiple FEs to be present in an NE. [3] 534 dictates that the ForCES protocol must be able to scale to at least 535 hundreds of FEs (see [3] Section 5, requirement #11). Each of 536 these FEs may potentially have a different set of packet processing 537 functions, with different media interfaces. FEs are responsible 538 for basic maintenance of layer-2 connectivity with other FEs and 539 with external entities. Many layer-2 media include sophisticated 540 control protocols. The FORCES protocol (over the Fp reference 541 point) will be able to carry messages for such protocols so that, 542 in keeping with the dumb FE model, the CE can provide appropriate 543 intelligence and control over these media. 545 When multiple FEs are present, ForCES requires that packets must be 546 able to arrive at the NE by one FE and leave the NE via a different 547 FE (See [3], Section 5, Requirement #3). Packets that enter the NE 548 via one FE and leave the NE via a different FE are transferred 549 between FEs across the Fi reference point. Fi reference point 550 could be used by FEs to discovery their (inter-FE) topology, 551 perhaps during pre-association phase. The Fi reference point is a 552 separate protocol from the Fp reference point and is not currently 553 defined by the ForCES architecture. 555 FEs could be connected in different kinds of topologies and packet 556 processing may spread across several FEs in the topology. Hence, 557 logical packet flow may be different from physical FE topology. 558 Figure 6 provides some topology examples. When it is necessary to 559 forward packets between FEs, the CE needs to understand the FE 560 topology. The FE topology can be queried from the FEs by CEs. 562 ----------------- 563 | CE | 564 ----------------- 565 ^ ^ ^ 566 / | \ 567 / v \ 568 / ------- \ 569 / +->| FE3 |<-+ \ 570 / | | | | \ 571 v | ------- | v 572 ------- | | ------- 573 | FE1 |<-+ +->| FE2 | 574 | |<--------------->| | 575 ------- ------- 576 ^ | ^ | 577 | | | | 578 | v | v 580 (a) Full mesh among FE1, FE2 and FE3. 582 ----------- 583 | CE | 584 ----------- 585 ^ ^ ^ ^ 586 / | | \ 587 /------ | | ------\ 588 v v v v 589 ------- ------- ------- ------- 590 | FE1 |<->| FE2 |<->| FE3 |<->| FE4 | 591 ------- ------- ------- ------- 592 ^ | ^ | ^ | ^ | 593 | | | | | | | | 594 | v | v | v | v 596 (b) Multiple FEs in a daisy chain 598 ^ | 599 | v 600 ----------- 601 | FE1 |<-----------------------| 602 ----------- | 603 ^ ^ | 604 / \ | 605 | ^ / \ ^ | V 606 v | v v | v ---------- 607 --------- --------- | | 608 | FE2 | | FE3 |<------------>| CE | 609 --------- --------- | | 610 ^ ^ ^ ---------- 611 | \ / ^ ^ 612 | \ / | | 613 | v v | | 614 | ----------- | | 615 | | FE4 |<----------------------| | 616 | ----------- | 617 | | ^ | 618 | v | | 619 | | 620 |----------------------------------------| 622 (c) Multiple FEs connected by a ring 624 Figure 6. Some examples of FE topology. 626 3.3.CE Managers 628 CE managers are responsible for determining which FEs a CE should 629 control. It is legitimate for CE managers to be hard-coded with 630 the knowledge of with which FEs its CEs should communicate with. A 631 CE manager may also be physically embedded into a CE and be 632 implemented as a simple keypad or other direct configuration 633 mechanism on the CE. Finally, CE managers may be physically and 634 logically separate entities that configure the CE with FE 635 information via such mechanisms as COPS-PR [6] or SNMP [4]. 637 3.4. FE Managers 639 FE managers are responsible for determining with which CE any 640 particular FE should initially communicate. Like CE managers, no 641 restrictions are placed on how an FE manager decides with which CE 642 its FEs should communicate, nor are restrictions placed on how FE 643 managers are implemented. Each FE should have one and only one FE 644 manager, while different FEs may have the same or different FE 645 manager(s). Each manager can choose to exist and operate 646 independently of other manager. 648 4. Operational Phases 650 Both FEs and CEs require some configuration in place before they 651 can start information exchange and function as a coherent network 652 element. Two operational phases are identified in this framework: 653 pre-association and post-association. 655 4.1.Pre-association Phase 657 Pre-association phase is the period of time during which an FE 658 Manager and a CE Manager are determining which FE and CE should be 659 part of the same network element. The protocols used during this 660 phase may include all or some of the message exchange over Fl, Ff 661 and Fc reference points. However, all these may be optional and 662 none of this is within the scope of ForCES protocol. 664 4.1.1. Fl Reference Point 666 CE managers and FE managers may communicate across the Fl reference 667 point in the pre-association phase in order to determine which CEs 668 and FEs should communicate with each other. Communication across 669 the Fl reference point is optional in this architecture. No 670 requirements are placed on this reference point. 672 CE managers and FE managers may be operated by different entities. 673 The operator of the CE manager may not want to divulge, except to 674 specified FE managers, any characteristics of the CEs it manages. 675 Similarly, the operator of the FE manager may not want to divulge 676 FE characteristics, except to authorized entities. As such, CE 677 managers and FE managers may need to authenticate one another. 678 Subsequent communication between CE managers and FE managers may 679 require other security functions such as privacy, non-repudiation, 680 freshness, and integrity. 682 FE Manager FE CE Manager CE 683 | | | | 684 | | | | 685 |(security exchange) | | 686 1|<------------------------------>| | 687 | | | | 688 |(a list of CEs and their attributes) | 689 2|<-------------------------------| | 690 | | | | 691 |(a list of FEs and their attributes) | 692 3|------------------------------->| | 693 | | | | 694 | | | | 695 |<----------------Fl------------>| | 697 Figure 7. An example of message exchange over Fl reference point 699 Once the necessary security functions have been performed, the CE 700 and FE managers communicate to determine which CEs and FEs should 701 communicate with each other. At the very minimum, the CE and FE 702 managers need to learn of the existence of available FEs and CEs 703 respectively. This discovery process may entail one or both 704 managers learning the capabilities of the discovered ForCES 705 protocol elements. Figure 7 shows an example of possible message 706 exchange between CE manager and FE manager over Fl reference point. 708 4.1.2. Ff Reference Point 710 The Ff reference point is used to inform forwarding elements of the 711 association decisions made by the FE manager in pre-association 712 phase. Only authorized entities may instruct an FE with respect to 713 which CE should control it. Therefore, privacy, integrity, 714 freshness, and authentication are necessary between the FE manager 715 and FEs when the FE manager is remote to the FE. Once the 716 appropriate security has been established, the FE manager instructs 717 the FEs across this reference point to join a new NE or to 718 disconnect from an existing NE. The FE Manager could also assign 719 unique FE identifiers to the FEs using this reference point. The 720 FE identifiers are useful in post association phase to express FE 721 topology. Figure 8 shows example of message exchange over Ff 722 reference point. 724 FE Manager FE CE Manager CE 725 | | | | 726 | | | | 727 |(security exchange) |(security exchange) 728 1|<------------>|authentication 1|<----------- 729 >|authentication | | | 730 | 731 |(FE ID, attributes) |(CE ID, attributes) 732 2|<-------------|request 2|<------------|request 733 | | | | 734 3|------------->|response 3|------------>|response 735 |(corresponding CE ID) |(corresponding FE ID) 736 | | | | 737 | | | | 738 |<-----Ff----->| |<-----Fc---->| 740 Figure 8. Examples of message exchange 741 over Ff and Fc reference points. 743 Note that the FE manager function may be co-located with the FE 744 (such as by manual keypad entry of the CE IP address), in which 745 case this reference point is reduced to a built-in function. 747 4.1.3. Fc Reference Point 749 The Fc reference point is used to inform control elements of the 750 association decisions made by CE managers in pre-association phase. 751 When the CE manager is remote, only authorized entities may 752 instruct a CE to control certain FEs. Privacy, integrity, 753 freshness and authentication are also required across this 754 reference point in such a configuration. Once appropriate security 755 has been established, the CE manager instructs CEs as to which FEs 756 they should control and how they should control them. Figure 8 757 shows example of message exchange over Fc reference point. 759 As with the FE manager and FEs, configurations are possible where 760 the CE manager and CE are co-located and no protocol is used for 761 this function. 763 4.2. Post-association Phase and Fp reference point 765 Post-association phase is the period of time during which an FE and 766 CE have been configured with information necessary to contact each 767 other and includes both association establishment and steady-state 768 communication. The communication between CE and FE is performed 769 across the Fp ("p" meaning protocol) reference point. ForCES 770 protocol is exclusively used for all communication across the Fp 771 reference point. 773 4.2.1. Proximity and Interconnect between CEs and FEs 775 The ForCES Working Group has made a conscious decision that the 776 first version of ForCES will not be designed to support 777 configurations where the CE and FE are located arbitrarily in the 778 network. In particular, ForCES is intended for "very close" CE/FE 779 localities in IP networks, as defined by ForCES Applicability 780 Statement ([7]). Very Close localities consist of control and 781 forwarding elements that either are components in the same physical 782 box, or are separated at most by one local network hop. CEs and 783 FEs can be connected by a variety of interconnect technologies, 784 including Ethernet connections, backplanes, ATM (cell) fabrics, 785 etc. ForCES should be able to support each of these interconnects 786 (see [3] Section 5, requirement #1). When the CEs and FEs are 787 separated beyond a single L3 routing hop, the ForCES protocol will 788 make use of an existing RFC2914 compliant L4 protocol with adequate 789 reliability, security and congestion control (e.g. TCP, SCTP) for 790 transport purposes. 792 4.2.2. Association Establishment 794 FE CE 795 | | 796 |(Security exchange.) | 797 1|<--------------------->| 798 | | 799 |(Let me join the NE please.) 800 2|---------------------->| 801 | | 802 |(What kind of FE are you? -- capability query) 803 3|<----------------------| 804 | | 805 |(Here is my FE functions/state: use model to 806 describe) 807 4|---------------------->| 808 | | 809 |(How are you connected with other FEs?) 810 5|<----------------------| 811 | | 812 |(Here is the FE topology info) 813 6|---------------------->| 814 | | 815 |(Initial config for FE -- optional) 816 7|<----------------------| 817 | | 818 |(I am ready to go. Shall I?) 819 8|---------------------->| 820 | | 821 |(Go ahead!) | 822 9|<----------------------| 823 | | 825 Figure 9. Example of message exchange between CE and FE 826 over Fp to establish NE association 828 As an example, figure 9 shows some of the message exchange that may 829 happen before the association between the CE and FE is fully 830 established. Either the CE or FE can initiate the connection. 831 Security handshake is necessary to authenticate the two 832 communication endpoints to each other before any further message 833 exchange can happen. The exact details of the security handshake 834 depend on the security solution chosen by ForCES protocol. It is 835 most likely that either IPSec or TLS will be used. Section 9 836 provides more details on the security considerations for ForCES. 837 After the successful security handshake, the FE needs to inform the 838 CE of its own capability and its topology in relation to other FEs. 839 The capability of the FE is represented by the FE model, described 840 in a separate document. The model would allow an FE to describe 841 what kind of packet processing functions it contains, in what order 842 the processing happens, what kinds of configurable parameters it 843 allows, what statistics it collects and what events it might throw, 844 etc. Once such information is available to the CE, the CE may 845 choose to send some initial or default configuration to the FE so 846 that the FE can start receiving and processing packets correctly. 847 Such initialization may not be necessary if the FE already obtains 848 the information from its own bootstrap process. Once FE starts 849 accepting packets for processing, we say the association of this FE 850 with its CE is now established. From then on, the CE and FE enter 851 steady-state communication. 853 4.2.3. Steady-state Communication 855 Once an association is established between the CE and FE, the 856 ForCES protocol is used by the CE and FE over Fp reference point to 857 exchange information to facilitate packet processing. 859 FE CE 860 | | 861 |(Add these new routes.)| 862 1|<----------------------| 863 | | 864 |(Successful.) | 865 2|---------------------->| 866 | | 867 | | 868 |(Query some stats.) | 869 1|<----------------------| 870 | | 871 |(Reply with stats collected.) 872 2|---------------------->| 873 | | 874 | | 875 |(My port is down, with port #.) 876 1|---------------------->| 877 | | 878 |(Here is a new forwarding table) 880 2|<----------------------| 881 | | 882 Figure 10. Examples of message exchange between CE and FE 883 over Fp during steady-state communication 885 Based on the information acquired through CEs' control processing, 886 CEs will frequently need to manipulate the packet-forwarding 887 behaviors of their FE(s) by sending instructions to FEs. For 888 example, Figure 10 shows message exchange examples in which the CE 889 sends new routes to the FE so that the FE can add them to its 890 forwarding table. The CE may query the FE for statistics collected 891 by the FE and the FE may notify the CE of important events such as 892 port failure. 894 4.2.4. Data Packets across Fp reference point 896 --------------------- ---------------------- 897 | | | | 898 | +--------+ | | +--------+ | 899 | |CE(BGP) | | | |CE(BGP) | | 900 | +--------+ | | +--------+ | 901 | | | | ^ | 902 | |Fp | | |Fp | 903 | v | | | | 904 | +--------+ | | +--------+ | 905 | | FE | | | | FE | | 906 | +--------+ | | +--------+ | 907 | | | | ^ | 908 | Router | | | Router | | 909 | A | | | B | | 910 ---------+----------- -----------+---------- 911 v ^ 912 | | 913 | | 914 ------------------->--------------- 916 Figure 11. Example to show data packet flow between two NEs. 918 Control plane protocol packets (such as RIP, OSPF messages) 919 addressed to any of NE's interfaces are typically redirected by the 920 receiving FE to its CE, and CE may originate packets and have its 921 FE deliver them to other NEs. Therefore, ForCES protocol over Fp 922 not only transports the ForCES protocol messages between CEs and 923 FEs, but also encapsulates the data packets from control plane 924 protocols. Moreover, one FE may be controlled by multiple CEs for 925 distributed control. In this configuration, the control protocols 926 supported by the FORCES NEs may spread across multiple CEs. For 927 example, one CE may support routing protocols like OSPF and BGP, 928 while a signaling and admission control protocol like RSVP is 929 supported in another CE. FEs are configured to recognize and 930 filter these protocol packets and forward them to the corresponding 931 CE. 933 Figure 11 shows one example of how the BGP packets originated by 934 router A are passed to router B. In this example, the ForCES 935 protocol is used to transport the packets from the CE to the FE 936 inside router A, and then from the FE to the CE inside router B. 937 In light of the fact that the ForCES protocol is responsible for 938 transporting both the control messages and the data packets between 939 the CE and FE over Fp reference point, it is possible to use either 940 a single protocol or multiple protocols to achieve this. 942 4.2.5. Proxy FE 944 In the case where a physical FE cannot implement (e.g., due to the 945 lack of a general purpose CPU) the ForCES protocol directly, a 946 proxy FE can be used in the middle of Fp reference point. This 947 allows the CE communicate to the physical FE via the proxy by using 948 ForCES, while the proxy manipulates the physical FE using some 949 intermediary form of communication (e.g., a non-ForCES protocol or 950 DMA). In such an implementation, the combination of the proxy and 951 the physical FE becomes one logical FE entity. 953 4.3. Association Re-establishment 955 FEs and CEs may join and leave NEs dynamically (see [3] Section 5, 956 requirements #12). When an FE or CE leaves the NE, the association 957 with the NE is broken. If the leaving party rejoins an NE later, 958 to re-establish the association, it may need to re-enter the pre- 959 association phase. Loss of association can also happen 960 unexpectedly due to loss of connection between the CE and the FE. 961 Therefore, the framework allows the bi-directional transition 962 between these two phases, but the ForCES protocol is only 963 applicable for the post-association phase. However, the protocol 964 should provide mechanisms to support association re-establishment. 965 This includes the ability for CEs and FEs to determine when there 966 is a loss of association between them, ability to restore 967 association and efficient state (re)synchronization mechanisms (see 968 [3] Section 5, requirement #7). Note that security association and 969 state must be also re-established to guarantee the same level of 970 security exists before and after the association re-establishment. 972 4.3.1. CE graceful restart 973 The failure and restart of the CE in a router can potentially cause 974 much stress and disruption on the control plane throughout a 975 network. Because when a CE has to restart for any reason, the 976 router loses routing adjacencies or sessions with its routing 977 neighbors. Neighbors who detect the lost adjacency normally re- 978 compute new routes and then send routing updates to their own 979 neighbors to communicate the lost adjacency. Their neighbors do 980 the same thing to propagate throughout the network. In the 981 meantime, the restarting router cannot receive traffic from other 982 routers because the neighbors have stopped using the router's 983 previously advertised routes. When the restarting router restores 984 adjacencies, neighbors must once again re-compute new routes and 985 send out additional routing updates. The restarting router is 986 unable to forward packets until it has re-established routing 987 adjacencies with neighbors, received route updates through these 988 adjacencies, and computed new routes. Until convergence takes 989 place throughout the network, packets may be lost in transient 990 black holes or forwarding loops. 992 A high availability mechanism known as the "graceful restart" has 993 been used by the IP routing protocols (OSPF [10], BGP [11], BGP 994 [11]) and MPLS label distribution protocol (LDP [9]) to help 995 minimize the negative effects on routing throughout an entire 996 network caused by a restarting router. Route flap on neighboring 997 routers is avoided, and a restarting router can continue to forward 998 packets that would otherwise be dropped. 1000 While the details differ from protocol to protocol, the general 1001 idea behind the graceful restart mechanism remains the same. With 1002 the graceful restart, a restarting router can inform its neighbors 1003 when it restarts. The neighbors may detect the lost adjacency but 1004 do not recompute new routes or send routing updates to their 1005 neighbors. The neighbors also hold on to the routes received from 1006 the restarting router before restart and assume they are still 1007 valid for a limited time. By doing so, the restarting router's FEs 1008 can also continue to receive and forward traffic from other 1009 neighbors for a limited time by using the routes they already have. 1010 The restarting router then re-establishes routing adjacencies, 1011 downloads updated routes from all its neighbors, recomputes new 1012 routes and uses them to replace the older routes it was using. It 1013 then sends these updated routes to its neighbors and signals the 1014 completion of the graceful restart process. 1016 Non-stop forwarding is a requirement for graceful restart. It is 1017 necessary so a router can continue to forward packets while it is 1018 downloading routing information and recomputing new routes. This 1019 ensures that packets will not be dropped. As one can see, one of 1020 the benefits afforded by the separation of CE and FE is exactly the 1021 ability of non-stop forwarding in the face of the CE failure and 1022 restart. The support of dynamic changes to CE/FE association in 1023 ForCES also makes it compatible with high availability mechanisms 1024 such as graceful restart. 1026 ForCES should be able to support CE graceful restart easily. When 1027 the association is established the first time, the CE must inform 1028 the FEs what to do in the case of CE failure. If graceful restart 1029 is not supported, the FEs may be told to stop packet processing all 1030 together if its CE fails. If graceful restart is supported, the 1031 FEs should be told to cache and hold on to its FE state including 1032 the forwarding tables across the restarts. A timer must be 1033 included so that the timeout causes such cached state to expire 1034 eventually. Those timers should be settable by the CE. 1036 4.3.2. FE restart 1038 In the same example in Figure 5, assuming CE1 is the working CE for 1039 the moment, what would happen if one of the FEs, say FE1, leaves 1040 the NE temporarily? FE1 may voluntarily decide to leave the 1041 association. Alternatively, FE1 may stop functioning simply due to 1042 unexpected failure. In former case, CE1 receives a "leave- 1043 association request" from FE1. In the latter, CE1 detects the 1044 failure of FE1 by some other means. In both cases, CE1 must inform 1045 the routing protocols of such an event, most likely prompting a 1046 reachability and SPF (Shortest Path First) recalculation and 1047 associated downloading of new FIBs from CE1 to the other remaining 1048 FEs (only FE2 in this example). Such recalculation and FIB update 1049 will also be propagated from the CE1 to its neighbors that are 1050 affected by the connectivity of FE1. 1052 When FE1 decides to rejoin again, or when it restarts again from 1053 the failure, FE1 needs to re-discover its master (CE). This can be 1054 achieved by several means. It may re-enter the pre-association 1055 phase and get that information from its FE manager. It may 1056 retrieve the previous CE information from its cache, if it can 1057 validate the information freshness. Once it discovers its CE, it 1058 starts message exchange with CE to re-establish the association 1059 just as outlined in Figure 9, with the possible exception that it 1060 might be able to bypass the transport of the complete initial 1061 configuration. Suppose that FE1 still has its routing table and 1062 other state information from the last association, instead of 1063 sending all the information again from scratch, it may be able to 1064 use more efficient mechanism to re-sync up the state with its CE if 1065 such mechanism is supported by the ForCES protocol. For example, 1066 CRC-32 of the state might give a quick indication of whether or not 1067 the state is in-sync with its CE. By comparing its state with CE 1068 first, it sends information update only if it is needed. ForCES 1069 protocol may choose to implement similar optimization mechanisms, 1070 but it may also choose not to, as this is not a requirement. 1072 5. Applicability to RFC1812 1074 [3] Section 5, requirement #9 dictates "Any proposed ForCES 1075 architecture must explain how that architecture supports all of the 1076 router functions as defined in RFC1812." RFC1812 discusses many 1077 important requirements for IPv4 routers from the link layer to the 1078 application layer. This section addresses the relevant 1079 requirements in RFC1812 for implementing IPv4 routers based on 1080 ForCES architecture and explains how ForCES satisfies these 1081 requirements by providing guidelines on how to separate the 1082 functionalities required into forwarding plane and control plane. 1084 In general, the forwarding plane carries out the bulk of the per- 1085 packet processing that is required at line speed, while the control 1086 plane carries most of the computationally complex operations that 1087 are typical of the control and signaling protocols. However, it is 1088 impossible to draw a rigid line to divide the processing into CEs 1089 and FEs cleanly. Nor should the ForCES architecture limit the 1090 innovative approaches in control and forwarding plane separation. 1091 As more and more processing power is available in the FEs, some of 1092 the control functions that traditionally are performed by CEs may 1093 now be moved to FEs for better performance and scalability. Such 1094 offloaded functions may include part of ICMP or TCP processing, or 1095 part of routing protocols. Once off-loaded onto the forwarding 1096 plane, such CE functions, even though logically belonging to the 1097 control plane, now become part of the FE functions. Just like the 1098 other logical functions performed by FEs, such off-loaded functions 1099 must be expressed as part of the FE model so that the CEs can 1100 decide how to best take advantage of these off-loaded functions 1101 when present on the FEs. 1103 5.1. General Router Requirements 1105 Routers have at least two or more logical interfaces. When CEs and 1106 FEs are separated by ForCES within a single NE, some additional 1107 interfaces are needed for intra-NE communications. Figure 12 shows 1108 an example to illustrate that. This NE contains one CE and two 1109 FEs. Each FE has four interfaces; two of them are used for 1110 receiving and transmitting packets to the external world, while the 1111 other two are for intra-NE connections. CE has two logical 1112 interfaces #9 and #10, connected to interfaces #3 and #6 from FE1 1113 and FE2, respectively. Interface #4 and #5 are connected for FE1- 1114 FE2 communication. Therefore, this router NE provides four 1115 external interfaces (#1, 2, 7 and 8). 1117 --------------------------------- 1118 | router NE | 1119 | ----------- ----------- | 1120 | | FE1 | | FE2 | | 1121 | ----------- ----------- | 1122 | 1| 2| 3| 4| 5| 6| 7| 8| | 1123 | | | | | | | | | | 1124 | | | | +----+ | | | | 1125 | | | | | | | | 1126 | | | 9| 10| | | | 1127 | | | -------------- | | | 1128 | | | | CE | | | | 1129 | | | -------------- | | | 1130 | | | | | | 1131 -----+--+----------------+--+---- 1132 | | | | 1133 | | | | 1135 Figure 12. A router NE example with four interfaces. 1137 IPv4 routers must implement IP to support its packet forwarding 1138 function, which is driven by its FIB (Forwarding Information Base). 1139 This Internet layer forwarding (see RFC1812 [1] Section 5) 1140 functionality naturally belongs to FEs in the ForCES architecture. 1142 A router may implement transport layer protocols (like TCP and UDP) 1143 that are required to support application layer protocols (see 1144 RFC1812 [1] Section 6). One important class of application 1145 protocols is routing protocols (see RFC1812 [1] Section 7). In 1146 ForCES architecture, routing protocols are naturally implemented by 1147 CEs. Routing protocols require routers communicate with each 1148 other. This communication between CEs in different routers is 1149 supported in ForCES by FEs' ability to redirect data packets 1150 addressed to routers (i.e., NEs) and CEs' ability to originate 1151 packets and have them delivered by their FEs. This communication 1152 occurs across Fp reference point inside each router and between 1153 neighboring routers' external interfaces, as illustrated in Figure 1154 11. 1156 5.2.Link Layer 1158 Since FEs own all the external interfaces for the router, FEs need 1159 to conform to the link layer requirements in RFC1812. Arguably, 1160 ARP support may be implemented in either CEs or FEs. As we will 1161 see later, a number of behaviors that RFC1812 mandates fall into 1162 this category -- they may be performed by the FE and may be 1163 performed by the CE. A general guideline is needed to ensure 1164 interoperability between separated control and forwarding planes. 1165 The guideline we offer here is that CEs MUST be capable of these 1166 kind of operations while FEs MAY choose to implement them. FE 1167 model should indicate its capabilities in this regard so that CEs 1168 can decide where these functions are implemented. 1170 Interface parameters, including MTU, IP address, etc., must be 1171 configurable by CEs via ForCES. CEs must be able to determine 1172 whether a physical interface in an FE is available to send packets 1173 or not. FEs must also inform CEs the status change of the 1174 interfaces (like link up/down) via ForCES. 1176 5.3.Internet Layer Protocols 1178 Both FEs and CEs must implement IP protocol and all mandatory 1179 extensions as RFC1812 specified. CEs should implement IP options 1180 like source route and record route while FEs may choose to 1181 implement those as well. The timestamp option should be 1182 implemented by FEs to insert the timestamp most accurately. The FE 1183 must interpret the IP options that it understands and preserve the 1184 rest unchanged for use by CEs. Both FEs and CEs might choose to 1185 silently discard packets without sending ICMP errors, but such 1186 events should be logged and counted. FEs may report statistics for 1187 such events to CEs via ForCES. 1189 When multiple FEs are involved to process packets, the appearance 1190 of single NE must be strictly maintained. For example, Time-To- 1191 Live (TTL) must be decremented only once within a single NE. For 1192 example, it can be always decremented by the last FE with egress 1193 function. 1195 FEs must receive and process normally any packets with a broadcast 1196 destination address or a multicast destination address that the 1197 router has asked to receive. When IP multicast is supported in 1198 routers, IGMP is implemented in CEs. CEs are also required of ICMP 1199 support, while it is optional for FEs to support ICMP. Such an 1200 option can be communicated to CEs as part of the FE model. 1201 Therefore, FEs can always rely upon CEs to send out ICMP error 1202 messages, but FEs also have the option to generate ICMP error 1203 messages themselves. 1205 5.4.Internet Layer Forwarding 1206 IP forwarding is implemented by FEs. When the routing table is 1207 updated at CEs, ForCES is used to send the new route entries from 1208 CEs to FEs. Each FE has its own forwarding table and uses this 1209 table to direct packets to the next hop interface. 1211 Upon receiving IP packets, the FE verifies the IP header and 1212 processes most of the IP options. Some options cannot be processed 1213 until the routing decision has been made. The routing decision is 1214 made after examining the destination IP address. If the 1215 destination address belongs to the router itself, the packets are 1216 filtered and either processed locally or forwarded to CE, depending 1217 upon the instructions set-up by CE. Otherwise, the FE determines 1218 the next hop IP address by looking up in its forwarding table. The 1219 FE also determines the network interface it uses to send the 1220 packets. Sometimes an FE may need to forward the packets to 1221 another FE before packets can be forwarded out to the next hop. 1222 Right before packets are forwarded out to the next hop, the FE 1223 decrements TTL by 1 and processes any IP options that cannot be 1224 processed before. The FE performs any IP fragmentation if 1225 necessary, determines link layer address (e.g., by ARP), and 1226 encapsulates the IP datagram (or each of the fragments thereof) in 1227 an appropriate link layer frame and queues it for output on the 1228 interface selected. 1230 Other options mentioned in RFC1812 for IP forwarding may also be 1231 implemented at FEs, for example, packet filtering. 1233 FEs typically forward packets destined locally to CEs. FEs may 1234 also forward exceptional packets (packets that FEs do not know how 1235 to handle) to CEs. CEs are required to handle packets forwarded by 1236 FEs for whatever different reasons. It might be necessary for 1237 ForCES to attach some meta-data with the packets to indicate the 1238 reasons of forwarding from FEs to CEs. Upon receiving packets with 1239 meta-data from FEs, CEs can decide to either process the packets 1240 themselves, or pass the packets to the upper layer protocols 1241 including routing and management protocols. If CEs are to process 1242 the packets by themselves, CEs may choose to discard the packets, 1243 or modify and re-send the packets. CEs may also originate new 1244 packets and deliver them to FEs for further forwarding. 1246 Any state change during router operation must also be handled 1247 correctly according to RFC1812. For example, when an FE ceases 1248 forwarding, the entire NE may continue forwarding packets, but it 1249 needs to stop advertising routes that are affected by the failed 1250 FE. 1252 5.5. Transport Layer 1253 Transport layer is typically implemented at CEs to support higher 1254 layer application protocols like routing protocols. In practice, 1255 this means that most CEs implement both the Transmission Control 1256 Protocol (TCP) and the User Datagram Protocol (UDP). 1258 Both CEs and FEs need to implement ForCES protocol. If some layer- 1259 4 transport is used to support ForCES, then both CEs and FEs need 1260 to implement the L4 transport and ForCES protocols. 1262 5.6. Application Layer -- Routing Protocols 1264 Interior and exterior routing protocols are implemented on CEs. 1265 The routing packets originated by CEs are forwarded to FEs for 1266 delivery. The results of such protocols (like forwarding table 1267 updates) are communicated to FEs via ForCES. 1269 For performance or scalability reasons, portions of the control 1270 plane functions that need faster response may be moved from the CEs 1271 and off-loaded onto the FEs. For example in OSPF, the Hello 1272 protocol packets are generated and processed periodically. When 1273 done at CEs, the inbound Hello packets have to traverse from the 1274 external interfaces at the FEs to the CEs via the internal CE-FE 1275 channel. Similarly, the outbound Hello packets have to go from the 1276 CEs to the FEs and to the external interfaces. Frequent Hello 1277 updates place heavy processing overhead on the CEs and can 1278 overwhelm the CE-FE channel as well. Since typically there are far 1279 more FEs than CEs in a router, the off-loaded Hello packets are 1280 processed in a much more distributed and scalable fashion. By 1281 expressing such off-loaded functions in the FE model, we can ensure 1282 interoperability. However, the exact description of the off-loaded 1283 functionality corresponding to the off-loaded functions expressed 1284 in the FE model are not part of the model itself and will need to 1285 be worked out as a separate specification. 1287 5.7. Application Layer -- Network Management Protocol 1289 RFC1812 also dictates "Routers MUST be manageable by SNMP." (see 1290 [4] Section 8) In general, for post-association phase, most 1291 external management tasks (including SNMP) should be done through 1292 interaction with the CE in order to support the appearance of a 1293 single functional device. Therefore, it is recommended that SNMP 1294 management agent be implemented by CEs and the SNMP messages 1295 received by FEs be redirected to their CEs. AgentX framework 1296 defined in RFC2741 ([5]) may be applied here such that CEs act in 1297 the role of master agent to process SNMP protocol messages while 1298 FEs act in the role of subagent to provide access to the MIB 1299 objects residing on FEs. AgentX protocol messages between the 1300 master agent (CE) and the subagent (FE) are encapsulated and 1301 transported via ForCES, just like data packets from any other 1302 application layer protocols. 1304 6. Summary 1306 This document defines an architectural framework for ForCES. It 1307 identifies the relevant components for a ForCES network element, 1308 including (one or more) FEs, (one or more) CEs, one optional FE 1309 manager, and one optional CE manager. It also identifies the 1310 interaction among these components and discusses all the major 1311 reference points. It is important to point out that, among all the 1312 reference points, only the Fp interface between CEs and FEs is 1313 within the scope of ForCES. ForCES alone may not be enough to 1314 support all desirable NE configurations. However, we believe that 1315 ForCES over Fp interface is the most important element in realizing 1316 physical separation and interoperability of CEs and FEs, and hence 1317 the first interface that ought to be standardized. Simple and 1318 useful configurations can still be implemented with only CE-FE 1319 interface being standardized, e.g., single CE with full-meshed FEs. 1321 7. Security Considerations 1323 In general, the physical separation of two entities usually results 1324 in a potentially insecure link between the two entities and hence 1325 much stricter security measurements are required. For example, we 1326 pointed out in Section 4.1 that authentication becomes necessary 1327 between CE manager and FE manager, between CE and CE manager, 1328 between FE and FE manager in some configurations. The physical 1329 separation of CE and FE also imposes serious security requirement 1330 for ForCES protocol over Fp interface. This section first attempts 1331 to describe the security threats that may be introduced by the 1332 physical separation of the FEs and the CEs, and then it provides 1333 recommendation and guidelines for secure operation and management 1334 of ForCES protocol over Fp interface based on existing standard 1335 security solutions. 1337 7.1. Analysis of Potential Threats Introduced by ForCES 1339 This section provides the threat analysis for ForCES, with a focus 1340 on Fp interface. Each threat is described in details with the 1341 effects on the ForCES protocol entities or/and the NE as a whole, 1342 and the required functionalities that need to be in place to defend 1343 the threat. 1345 7.1.1. "Join" or "Remove" Message Flooding on CEs 1346 Threats: A malicious node could send a stream of false "join NE" 1347 or "remove from NE" requests on behalf of non-existent or 1348 unauthorized FE to legitimate CEs at a very rapid rate and thereby 1349 create unnecessary state in the CEs. 1351 Effects: If by maintaining state for non-existent or unauthorized 1352 FEs, a CE may become unavailable for other processing and hence 1353 suffer from denial of service (DoS) attack similar to the TCP SYN 1354 DoS. If multiple CEs are used, the unnecessary state information 1355 may also be conveyed to multiple CEs via Fr interface (e.g., from 1356 the active CE to the stand-by CE) and hence subject multiple CEs to 1357 DoS attack. 1359 Requirement: A CE that receives a "join" or "remove" request 1360 should not create any state information until it has authenticated 1361 the FE endpoint. 1363 7.1.2. Impersonation Attack 1365 Threats: A malicious node can impersonate a CE or FE and send out 1366 false messages. 1368 Effects: The whole NE could be compromised. 1370 Requirement: The CE or FE must authenticate the message before 1371 accepting and processing it. 1373 7.1.3. Replay Attack 1375 Threat: A malicious node could replay the entire message previously 1376 sent by an FE or CE entity to get around authentication. 1378 Effect: The NE could be compromised. 1380 Requirement: Replay protection mechanism needs to be part of the 1381 security protocol to defend this attack. 1383 7.1.4. Attack during Fail Over 1385 Threat: A malicious node may exploit the CE fail-over mechanism to 1386 take over the control of NE. For example, suppose two CEs, say CE-A 1387 and CE-B, are controlling several FEs. CE-A is active and CE-B is 1388 stand-by. When CE-A fails, CE-B is taking over the active CE 1389 position. The FEs already had a trusted relationship with CE-A, 1390 but the FEs may not have the same trusted relationship established 1391 with CE-B prior to the fail-over. A malicious node can take over 1392 as CE-B if such trusted relationship is not established during the 1393 fail-over. 1395 Effect: The NE may be compromised after such insecure fail-over. 1397 Requirement: The level of trust relationship between the stand-by 1398 CE and the FEs must be as strong as the one between the active CE 1399 and the FEs. The security association between the FEs and the 1400 stand-by CE may be established prior to fail-over. If not already 1401 in place, such security association must be re-established before 1402 the stand-by CE takes over. 1404 7.1.5. Data Integrity 1406 Threats: A malicious node may inject false messages to legitimate 1407 CE or FE. 1409 Effect: An FE or CE receives the fabricated packet and performs 1410 incorrect or catastrophic operation. 1412 Requirement: Protocol messages require integrity protection. 1414 7.1.6. Data Confidentiality 1416 Threat: When FE and CE are physically separated, a malicious node 1417 may eavesdrop the messages in transit. Some of the messages are 1418 critical to the functioning of the whole network, while others may 1419 contain confidential business data. Leaking of such information 1420 may result in compromise even beyond the immediate CE or FE. 1422 Effect: Sensitive information might be exposed between CE and FE. 1424 Requirement: Data confidentiality between FE and CE must be 1425 available for sensitive information. 1427 7.1.7. Sharing security parameters 1429 Threat: Consider a scenario where several FEs communicating to the 1430 same CE share the same authentication keys for the Fp interface. 1431 If any FE or the CE is compromised, all other entities are 1432 compromised. 1434 Effect: The whole NE is compromised. 1436 Requirement: To avoid this side effect, it is better to configure 1437 different security parameters for each FE-CE communication over Fp 1438 interface. 1440 7.1.8. Denial of Service Attack via External Interface 1442 Threat: When an FE receives a packet that is destined for its CE, 1443 the FE forwards the packet over the Fp interface. Malicious node 1444 can generate huge message storm like routing protocol packets etc. 1445 through the external Fi/f interface so that the FE has to process 1446 and forward all packets to CE through Fp interface. 1448 Effect: CE encounters resource exhaustion and bandwidth starvation 1449 on Fp interface due to an overwhelming number of packets from FEs. 1451 Requirement: Rate limiting mechanism needs to be in place at both 1452 FE and CE. Rate Limiter can be configured at FE for each message 1453 type that are being received through Fi/F interface. 1455 7.2. Security Recommendations for ForCES 1457 The requirements document [3] suggested that ForCES protocol should 1458 support reliability over Fp interface, but no particular transport 1459 protocol is yet specified for ForCES. This framework document does 1460 not intend to specify the particular transport either, and so we 1461 only provide recommendations and guidelines based on the existing 1462 standard security protocols that can work with the common transport 1463 candidates suitable for ForCES. 1465 We review two existing security protocol solutions, namely IPsec 1466 (IP Security) [14] or TLS (Transport Layer Security) [13]. TLS 1467 works with reliable transports such as TCP or SCTP for unicast, 1468 while IPsec can be used with any transport (UDP, TCP, SCTP) and 1469 supports both unicast and multicast. Both TLS and IPsec can be 1470 used potentially to satisfy all of the security requirements for 1471 ForCES protocol. Other approaches may be used as well but are not 1472 documented here. 1474 When ForCES is deployed between CEs and FEs inside a box, 1475 authentication, confidentiality and integrity may be provided by 1476 the physical security of the box and so the security mechanisms may 1477 be turned off, depending on the networking topology and its 1478 administration policy. However, it is important to realize that 1479 even if the NE is in a single-box, the DoS attacks as described in 1480 Section 7.1.8 can still be launched through Fi/f interfaces. 1481 Therefore, it is important to have the corresponding counter- 1482 measurement in place even for single-box deployment. 1484 7.2.1. Security Configuration 1486 The NE administrator has the freedom to determine the exact 1487 security configuration that is needed for the specific deployment. 1488 For example, ForCES may be deployed between CEs and FEs connected 1489 to each other inside a box over a backplane. In such scenario, 1490 physical security of the box ensures that most of the attacks such 1491 as man-in-the-middle, snooping, and impersonation are not possible, 1492 and hence ForCES architecture may rely on the physical security of 1493 the box to defend against these attacks and protocol mechanisms may 1494 be turned off. However, it is also shown that denial of service 1495 attack via external interface as described in Section 7.1.8 is 1496 still a potential threat even for such "all-in-one-box" deployment 1497 scenario and hence the rate limiting mechanism is still necessary. 1498 This is just one example to show that it is important to assess the 1499 security needs of the ForCES-enabled network elements under 1500 different deployment scenarios. It should be possible for the 1501 administrator to configure the level of security needed for the 1502 ForCES protocol. 1504 7.2.2. Using TLS with ForCES 1506 TLS [13] can be used if a reliable unicast transport such as TCP or 1507 SCTP is used for ForCES over the Fp interface. The TLS handshake 1508 protocol is used during association establishment or re- 1509 establishment phase to negotiate a TLS session between the CE and 1510 FE. Once the session is in place, the TLS record protocol is used 1511 to secure ForCES communication messages between the CE and FE. 1513 A basic outline of how TLS can be used with ForCES is described 1514 below. Steps 1) till 7) complete the security handshake as 1515 illustrated in Figure 9 while step 8) is for all the further 1516 communication between the CE and FE, including the rest of messages 1517 after the security handshake shown in Figure 9 and the steady-state 1518 communication shown in Figure 10. 1520 1) During Pre-association phase all FEs are configured with 1521 the CEs (including both the active CE and the standby CE). 1522 2) The FE establishes a TLS connection with the CE (master) 1523 and negotiates a cipher suite. 1524 3) The FE (slave) gets the CE certificate, validates the 1525 signature, checks the expiration date, checks if the 1526 certificate has been revoked. 1527 4) The CE (master) gets the FE certificate and performs the 1528 same validation as the FE in step 3). 1530 5) If any of the check fails in step 3) or step 4), endpoint 1531 must generate an error message and abort. 1532 6) After successful mutual authentication, a TLS session is 1533 established between CE and FE. 1534 7) The FE sends a "join NE" message to the CE. 1535 8) The FE and CE use TLS session for further communication. 1537 Note that there are different ways for the CE and FE to validate a 1538 received certificate. One way is to configure the FE Manager or CE 1539 Manager or other central component as CA, so that the CE or FE can 1540 query this pre-configured CA to validate that the certificate has 1541 not been revoked. Another way is to have the CE and the FE 1542 configured directly a list of valid certificates in the pre- 1543 association phase. 1545 In the case of fail-over, it is the responsibility of the active CE 1546 and the standby CE to synchronize ForCES states including the TLS 1547 states to minimize the state reestablishment during fail-over. 1548 Care must be taken to ensure that the standby CE is also 1549 authenticated in the same way as the active CE, either before or 1550 during the fail-over. 1552 7.2.3. Using IPsec with ForCES 1554 IPsec [14] can be used with any transport protocol, such as UDP, 1555 SCTP and TCP over Fp interface for ForCES. When using IPsec, we 1556 recommend using ESP in transport mode for ForCES because message 1557 confidentiality is required for ForCES. 1559 IPsec can be used with both manual and automated SA and 1560 cryptographic key management. But Ipsec's replay protection 1561 mechanisms are not available if manual key management is used. 1562 Hence, automatic key management is recommended if replay protection 1563 is deemed important. Otherwise, manual key management might be 1564 sufficient for some deployment scenarios, esp. when the number of 1565 CEs and FEs is relatively small. It is recommended that the keys 1566 be changed periodically even for manual key management. 1568 IPsec can support both unicast and multicast transport. When 1569 multicast is used, IPsec can be used with manual keying with no 1570 replay protection and no automatic rekeying. This meets the 1571 confidentiality and integrity requirements. Multicast-based 1572 solutions relying on IPsec should specify how rekeying and replay 1573 protection are provided. 1575 Unlike TLS, IPsec provides security services between the CE and FE 1576 at IP level, and so the security handshake as illustrated in Figure 1577 9 amounts to a "no-op" when manual key management is used. The 1578 following outline the steps taken for ForCES in such a case. 1580 1) During Pre-association phase all FEs are configured with 1581 the CEs (including active CE and standby CE) and SA parameters 1582 manually. 1583 2) The FE sends a "join NE" message to the CE. This message 1584 and all others that follow are afforded security service 1585 according to the manually configured IPsec SA parameters, but 1586 replay protection is not available. 1588 It is up to the administrator to decide whether to share the same 1589 key across multiple FE-CE communication, but it is recommended that 1590 different keys be used. Similarly, it is recommended that 1591 different keys be used for inbound and outbound traffic. 1593 If automatic key management is needed, IKE [15] can be used for 1594 that purpose. Other automatic key distribution techniques such as 1595 Kerberos may be used as well. The key exchange process 1596 constitutes the security handshake as illustrated in Figure 9. The 1597 following shows the steps involved in using IKE with IPsec for 1598 ForCES. Steps 1) to 6) constitute the security handshake in Figure 1599 9. 1601 1) During Pre-association phase all FEs are configured with 1602 the CEs (including active CE and standby CE), IPsec policy 1603 etc. 1604 2) The FE kicks off IKE process and tries to establish an 1605 IPsec SA with the CE (master). The FE (Slave) gets the CE 1606 certificate as part of the IKE negotiation. The FE validates 1607 signature, checks the expiration date, checks if the 1608 certificate has been revoked. 1609 3) The CE (master) gets the FE certificate and performs the 1610 same check as the FE in step 2). 1611 4) If any of the check fails in step 2) or step 3), the 1612 endpoint must generate an error message and abort. 1613 5) After successful mutual authentication, IPsec session is 1614 established between the CE and FE. 1615 6) The FE sends a "join NE" message to CE. No SADB entry is 1616 created in FE yet. 1617 7) The FE and CE use the IPsec session for further 1618 communication. 1620 FE Manager or CE Manager or other central component can be used as 1621 CA for validating CE and FE certificates during the IKE process. 1622 Alternatively, during the pre-association phase, the CE and FE can 1623 be configured directly with the required information such as 1624 certificates or passwords etc depending upon the type of 1625 authentication that administrator wants to configure. 1627 In the case of fail-over, it is the responsibility of active CE and 1628 standby CE to synchronize ForCES states and IPsec states to 1629 minimize the state reestablishment during fail-over. 1630 Alternatively, the FE needs to establish different IPsec SA during 1631 the startup operation itself with each CE. This will minimize the 1632 periodic state transfer across IPsec layer though Fr (CE-CE) 1633 Interface. 1635 8. Normative References 1637 [1] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, 1638 June 1995. 1640 [2] Floyd, S., "Congestion Control Principles", RFC 2914, September 1641 2000. 1643 [3] Khosravi, H. et al., "Requirements for Separation of IP Control 1644 and Forwarding", work in progress, May 2003, . 1647 9. Informative References 1649 [4] Case, J., et al., "A Simple Network Management Protocol 1650 (SNMP)", RFC 1157, May 1990. 1652 [5] Daniele, M. et al., "Agent Extensibility (AgentX) Protocol 1653 Version 1", RFC 2741, January 2000. 1655 [6] Chan, K. et al., "COPS Usage for Policy Provisioning (COPS- 1656 PR)", RFC 3084, March 2001. 1658 [7] Crouch, A. et al., "ForCES Applicability Statement", work in 1659 progress, June 2002, . 1661 [8] Anderson, T. and J. Buerkle, "Requirements for the Dynamic 1662 Partitioning of Switching Elements", RFC 3532, May 2003. 1664 [9] Leelanivas, M. et al., "Graceful Restart Mechanism for Label 1665 Distribution Protocol", RFC 3478, February 2003. 1667 [10] Moy, J. et al., "Graceful OSPF Restart", work in progress, 1668 March 2003, . 1670 [11] Sangli, S. et al., "Graceful Restart Mechanism for BGP", work 1671 in progress, January 2003, < draft-ietf-idr-restart-06.txt>. 1673 [12] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", work 1674 in progress, March 2003, . 1676 [13] Dierks, T. and C. Allen, "The TLS Protocol, version 1.0", RFC 1677 2246, January 1999. 1679 [14] Kent, S. and R. Atkinson, "Security Architecture for the 1680 Internet Protocol", RFC 2401, November 1998. 1682 [15] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE) ", 1683 RFC 2409, November 1998. 1685 [16] Bellovin, S., "Guidelines for Mandating the Use of Ipsec", 1686 work in progress, October 2002, . 1688 10. Acknowledgements 1690 Joel M. Halpern gave us many insightful comments and suggestions 1691 and pointed out several major issues. T. Sridhar suggested that 1692 the AgentX protocol could be used with SNMP to manage the ForCES 1693 network elements. Many of our colleagues and people in the ForCES 1694 mailing list also provided valuable feedback. 1696 11. Authors' Addresses 1698 Lily L. Yang 1699 Intel Corp., MS JF3-206, 1700 2111 NE 25th Avenue 1701 Hillsboro, OR 97124, USA 1702 Phone: +1 503 264 8813 1703 Email: lily.l.yang@intel.com 1705 Ram Dantu 1706 Department of Computer Science, 1707 University of North Texas, 1708 Denton, TX 76203, USA 1709 Phone: +1 940 565 2822 1710 Email: rdantu@unt.edu 1712 Todd A. Anderson 1713 Intel Corp. 1714 2111 NE 25th Avenue 1715 Hillsboro, OR 97124, USA 1716 Phone: +1 503 712 1760 1717 Email: todd.a.anderson@intel.com 1719 Ram Gopal 1720 Nokia Research Center 1721 5, Wayside Road, 1722 Burlington, MA 01803, USA 1723 Phone: +1 781 993 3685 1724 Email: ram.gopal@nokia.com 1726 12. Intellectual Property Right 1728 The IETF takes no position regarding the validity or scope of any 1729 intellectual property or other rights that might be claimed to 1730 pertain to the implementation or use of the technology described in 1731 this document or the extent to which any license under such rights 1732 might or might not be available; neither does it represent that it 1733 has made any effort to identify any such rights. Information on 1734 the IETF's procedures with respect to rights in standards-track and 1735 standards-related documentation can be found in RFC 2026. 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