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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-11) exists of draft-ietf-i2rs-problem-statement-08 == Outdated reference: A later version (-18) exists of draft-ietf-netconf-restconf-09 == Outdated reference: A later version (-14) exists of draft-ietf-netmod-rfc6020bis-09 -- Obsolete informational reference (is this intentional?): RFC 6536 (Obsoleted by RFC 8341) -- Obsolete informational reference (is this intentional?): RFC 7223 (Obsoleted by RFC 8343) -- Obsolete informational reference (is this intentional?): RFC 7277 (Obsoleted by RFC 8344) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Atlas 3 Internet-Draft Juniper Networks 4 Intended status: Informational J. Halpern 5 Expires: June 25, 2016 Ericsson 6 S. Hares 7 Huawei 8 D. Ward 9 Cisco Systems 10 T. Nadeau 11 Brocade 12 December 23, 2015 14 An Architecture for the Interface to the Routing System 15 draft-ietf-i2rs-architecture-12 17 Abstract 19 This document describes the IETF architecture for a standard, 20 programmatic interface for state transfer in and out of the Internet 21 routing system. It describes the basic architecture, the components, 22 and their interfaces with particular focus on those to be 23 standardized as part of the Interface to Routing System (I2RS). 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on June 25, 2016. 42 Copyright Notice 44 Copyright (c) 2015 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 1.1. Drivers for the I2RS Architecture . . . . . . . . . . . . 4 61 1.2. Architectural Overview . . . . . . . . . . . . . . . . . 5 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 63 3. Key Architectural Properties . . . . . . . . . . . . . . . . 11 64 3.1. Simplicity . . . . . . . . . . . . . . . . . . . . . . . 11 65 3.2. Extensibility . . . . . . . . . . . . . . . . . . . . . . 12 66 3.3. Model-Driven Programmatic Interfaces . . . . . . . . . . 12 67 4. Security Considerations . . . . . . . . . . . . . . . . . . . 13 68 4.1. Identity and Authentication . . . . . . . . . . . . . . . 15 69 4.2. Authorization . . . . . . . . . . . . . . . . . . . . . . 15 70 4.3. Client Redundancy . . . . . . . . . . . . . . . . . . . . 16 71 5. Network Applications and I2RS Client . . . . . . . . . . . . 16 72 5.1. Example Network Application: Topology Manager . . . . . . 17 73 6. I2RS Agent Role and Functionality . . . . . . . . . . . . . . 17 74 6.1. Relationship to its Routing Element . . . . . . . . . . . 17 75 6.2. I2RS State Storage . . . . . . . . . . . . . . . . . . . 18 76 6.2.1. I2RS Agent Failure . . . . . . . . . . . . . . . . . 18 77 6.2.2. Starting and Ending . . . . . . . . . . . . . . . . . 19 78 6.2.3. Reversion . . . . . . . . . . . . . . . . . . . . . . 19 79 6.3. Interactions with Local Configuration . . . . . . . . . . 20 80 6.4. Routing Components and Associated I2RS Services . . . . . 20 81 6.4.1. Routing and Label Information Bases . . . . . . . . . 21 82 6.4.2. IGPs, BGP and Multicast Protocols . . . . . . . . . . 22 83 6.4.3. MPLS . . . . . . . . . . . . . . . . . . . . . . . . 23 84 6.4.4. Policy and QoS Mechanisms . . . . . . . . . . . . . . 23 85 6.4.5. Information Modeling, Device Variation, and 86 Information Relationships . . . . . . . . . . . . . . 23 87 6.4.5.1. Managing Variation: Object Classes/Types and 88 Inheritance . . . . . . . . . . . . . . . . . . . 23 89 6.4.5.2. Managing Variation: Optionality . . . . . . . . . 24 90 6.4.5.3. Managing Variation: Templating . . . . . . . . . 24 91 6.4.5.4. Object Relationships . . . . . . . . . . . . . . 25 92 6.4.5.4.1. Initialization . . . . . . . . . . . . . . . 25 93 6.4.5.4.2. Correlation Identification . . . . . . . . . 25 94 6.4.5.4.3. Object References . . . . . . . . . . . . . . 26 95 6.4.5.4.4. Active Reference . . . . . . . . . . . . . . 26 96 7. I2RS Client Agent Interface . . . . . . . . . . . . . . . . . 26 97 7.1. One Control and Data Exchange Protocol . . . . . . . . . 26 98 7.2. Communication Channels . . . . . . . . . . . . . . . . . 26 99 7.3. Capability Negotiation . . . . . . . . . . . . . . . . . 27 100 7.4. Scope Policy Specifications . . . . . . . . . . . . . . . 27 101 7.5. Connectivity . . . . . . . . . . . . . . . . . . . . . . 28 102 7.6. Notifications . . . . . . . . . . . . . . . . . . . . . . 28 103 7.7. Information collection . . . . . . . . . . . . . . . . . 29 104 7.8. Multi-Headed Control . . . . . . . . . . . . . . . . . . 29 105 7.9. Transactions . . . . . . . . . . . . . . . . . . . . . . 30 106 8. Operational and Manageability Considerations . . . . . . . . 30 107 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 108 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 109 11. Informative References . . . . . . . . . . . . . . . . . . . 32 110 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 112 1. Introduction 114 Routers that form the internet routing infrastructure maintain state 115 at various layers of detail and function. For example, a typical 116 router maintains a Routing Information Base (RIB), and implements 117 routing protocols such as OSPF, IS-IS, and BGP to exchange 118 reachability information, topology information, protocol state, and 119 other information about the state of the network with other routers. 121 Routers convert all of this information into forwarding entries which 122 are then used to forward packets and flows between network elements. 123 The forwarding plane and the specified forwarding entries then 124 contain active state information that describes the expected and 125 observed operational behavior of the router and which is also needed 126 by the network applications. Network-oriented applications require 127 easy access to this information to learn the network topology, to 128 verify that programmed state is installed in the forwarding plane, to 129 measure the behavior of various flows, routes or forwarding entries, 130 as well as to understand the configured and active states of the 131 router. 133 This document sets out an architecture for a common, standards-based 134 interface to this information. This Interface to the Routing System 135 (I2RS) facilitates control and observation of the routing-related 136 state (for example, a Routing Element RIB manager's state), as well 137 as enabling network-oriented applications to be built on top of 138 today's routed networks. The I2RS is a programmatic asynchronous 139 interface for transferring state into and out of the internet routing 140 system. This I2RS architecture recognizes that the routing system 141 and a router's Operating System (OS) provide useful mechanisms that 142 applications could harness to accomplish application-level goals. 143 These network-oriented applications can leverage the I2RS 144 programmatic interface to create new ways of combining retrieval of 145 internet routing data, analyzing this data, setting state within 146 routers. 148 Fundamental to the I2RS are clear data models that define the 149 semantics of the information that can be written and read. The I2RS 150 provides a framework for registering and for requesting the 151 appropriate information for each particular application. The I2RS 152 provides a way for applications to customize network behavior while 153 leveraging the existing routing system as desired. 155 Although the I2RS architecture is general enough to support 156 information and data models for a variety of data, and aspects of the 157 I2RS solution may be useful in domains other than routing, I2RS and 158 this document are specifically focused on an interface for routing 159 data. 161 1.1. Drivers for the I2RS Architecture 163 There are four key drivers that shape the I2RS architecture. First 164 is the need for an interface that is programmatic, asynchronous, and 165 offers fast, interactive access for atomic operations. Second is the 166 access to structured information and state that is frequently not 167 directly configurable or modeled in existing implementations or 168 configuration protocols. Third is the ability to subscribe to 169 structured, filterable event notifications from the router. Fourth, 170 the operation of I2RS is to be data-model driven to facilitate 171 extensibility and provide standard data-models to be used by network 172 applications. 174 I2RS is described as an asynchronous programmatic interface, the key 175 properties of which are described in Section 5 of 176 [I-D.ietf-i2rs-problem-statement]. 178 The I2RS architecture facilitates obtaining information from the 179 router. The I2RS architecture provides the ability to not only read 180 specific information, but also to subscribe to targeted information 181 streams, filtered events, and thresholded events. 183 Such an interface also facilitates the injection of ephemeral state 184 into the routing system. Ephemeral state on a router is the state 185 which does not survive a the reboot of a routing device or the reboot 186 of the software handling the I2RS software on a routing device. A 187 non-routing protocol or application could inject state into a routing 188 element via the state-insertion functionality of the I2RS and that 189 state could then be distributed in a routing or signaling protocol 190 and/or be used locally (e.g. to program the co-located forwarding 191 plane). I2RS will only permit modification of state that would be 192 safe, conceptually, to modify via local configuration; no direct 193 manipulation of protocol-internal dynamically determined data is 194 envisioned. 196 1.2. Architectural Overview 198 Figure 1 shows the basic architecture for I2RS between applications 199 using I2RS, their associated I2RS Clients, and I2RS Agents. 200 Applications access I2RS services through I2RS clients. A single 201 client can provide access to one or more applications. This figure 202 also shows the types of data models associated with the routing 203 system (dynamic configuration, static configuration, local 204 configuration, and routing and signaling configuration) which the 205 I2RS Agent data models may access or augment. 207 Figure 1 is similar to the figure 1 found in the 208 [I-D.ietf-i2rs-problem-statement], but this figure shows additional 209 detail on how the applications utilize I2RS clients to interact with 210 I2RS Agents. Figure 1 also shows a logical view of the data models 211 associated with the routing system rather than a functional view 212 (RIB, FIB, topology, policy, routing/signaling protocols, etc.) 214 In figure 1, Clients A and B each provide access to a single 215 application (application A and B respectively), while Client P 216 provides access to multiple applications. 218 Applications can access I2RS services through local or remote 219 clients. A local client operates on the same physical box as routing 220 system. In contrast, a remote client operates across the network. 221 In the figure, Applications A and B access I2RS services through 222 local clients, while Applications C, D and E access I2RS services 223 through a remote client. The details of how applications communicate 224 with a remote client is out of scope for I2RS. 226 An I2RS Client can access one or more I2RS agents. In the figure 1, 227 Clients B and P access I2RS Agents 1 and 2. Likewise, an I2RS Agent 228 can provide service to one or more clients. In this figure, I2RS 229 Agent 1 provides services to Clients A, B and P while Agent 2 230 provides services to only Clients B and P. 232 I2RS agents and clients communicate with one another using an 233 asynchronous protocol. Therefore, a single client can post multiple 234 simultaneous requests, either to a single agent or to multiple 235 agents. Furthermore, an agent can process multiple requests, either 236 from a single client or from multiple clients, simultaneously. 238 The I2RS agent provides read and write access to selected data on the 239 routing element that are organized into I2RS Services. Section 4 240 describes how access is mediated by authentication and access control 241 mechanisms. Figure 1 shows I2RS agents being able to write ephemeral 242 static state (e.g. RIB entries), and to read from dynamic static 243 (e.g. MPLS LSP-ID or number of active BGP peers). In addition, the 245 In addition to read and write access, the I2RS agent allows clients 246 to subscribe to different types of notifications about events 247 affecting different object instances. One example of a notification 248 of such an event (which is unrelated to an object creation, 249 modification or deletion) is when a next-hop in the RIB is resolved 250 enough to be used by a RIB manager for installation in the forwarding 251 plane as part of a particular route. Please see Section 7.6 and 252 Section 7.7 for details. 254 The scope of I2RS is to define the interactions between the I2RS 255 agent and the I2RS client and the associated proper behavior of the 256 I2RS agent and I2RS client. 258 ****************** ***************** ***************** 259 * Application C * * Application D * * Application E * 260 ****************** ***************** ***************** 261 ^ ^ ^ 262 | | | 263 |--------------| | |--------------| 264 | | | 265 v v v 266 *************** 267 * Client P * 268 *************** 269 ^ ^ 270 | |-------------------------| 271 *********************** | *********************** | 272 * Application A * | * Application B * | 273 * * | * * | 274 * +----------------+ * | * +----------------+ * | 275 * | Client A | * | * | Client B | * | 276 * +----------------+ * | * +----------------+ * | 277 ******* ^ ************* | ***** ^ ****** ^ ****** | 278 | | | | | 279 | |-------------| | | |-----| 280 | | -----------------------| | | 281 | | | | | 282 ************ v * v * v ********* ***************** v * v ******** 283 * +---------------------+ * * +---------------------+ * 284 * | Agent 1 | * * | Agent 2 | * 285 * +---------------------+ * * +---------------------+ * 286 * ^ ^ ^ ^ * * ^ ^ ^ ^ * 287 * | | | | * * | | | | * 288 * v | | v * * v | | v * 289 * +---------+ | | +--------+ * * +---------+ | | +--------+ * 290 * | Routing | | | | Local | * * | Routing | | | | Local | * 291 * | and | | | | Config | * * | and | | | | Config | * 292 * |Signaling| | | +--------+ * * |Signaling| | | +--------+ * 293 * +---------+ | | ^ * * +---------+ | | ^ * 294 * ^ | | | * * ^ | | | * 295 * | |----| | | * * | |----| | | * 296 * v | v v * * v | v v * 297 * +----------+ +------------+ * * +----------+ +------------+ * 298 * | Dynamic | | Static | * * | Dynamic | | Static | * 299 * | System | | System | * * | System | | System | * 300 * | State | | State | * * | State | | State | * 301 * +----------+ +------------+ * * +----------+ +------------+ * 302 * * * * 303 * Routing Element 1 * * Routing Element 2 * 304 ******************************** ******************************** 306 Figure 1: Architecture of I2RS clients and agents 308 Routing Element: A Routing Element implements some subset of the 309 routing system. It does not need to have a forwarding plane 310 associated with it. Examples of Routing Elements can include: 312 * A router with a forwarding plane and RIB Manager that runs IS- 313 IS, OSPF, BGP, PIM, etc., 315 * A BGP speaker acting as a Route Reflector, 317 * An LSR that implements RSVP-TE, OSPF-TE, and PCEP and has a 318 forwarding plane and associated RIB Manager, 320 * A server that runs IS-IS, OSPF, BGP and uses ForCES to control 321 a remote forwarding plane, 323 A Routing Element may be locally managed, whether via CLI, SNMP, 324 or NETCONF. 326 Routing and Signaling: This block represents that portion of the 327 Routing Element that implements part of the internet routing 328 system. It includes not merely standardized protocols (i.e. IS- 329 IS, OSPF, BGP, PIM, RSVP-TE, LDP, etc.), but also the RIB Manager 330 layer. 332 Local Configuration: is the black box behavior for interactions 333 between the ephemeral state that I2RS installs into the routing 334 element; and this Local Configuration is defined by this document 335 and the behaviors specified by the I2RS protocol. 337 Dynamic System State: An I2RS agent needs access to state on a 338 routing element beyond what is contained in the routing subsystem. 339 Such state may include various counters, statistics, flow data, 340 and local events. This is the subset of operational state that is 341 needed by network applications based on I2RS that is not contained 342 in the routing and signaling information. How this information is 343 provided to the I2RS agent is out of scope, but the standardized 344 information and data models for what is exposed are part of I2RS. 346 Static System State: An I2RS agent needs access to static state on 347 a routing element beyond what is contained in the routing 348 subsystem. An example of such state is specifying queueing 349 behavior for an interface or traffic. How the I2RS agent modifies 350 or obtains this information is out of scope, but the standardized 351 information and data models for what is exposed are part of I2RS. 353 I2RS Agent: See the definition in Section 2. 355 Application: A network application that needs to observe the 356 network or manipulate the network to achieve its service 357 requirements. 359 I2RS Client: See the definition in Section 2. 361 As can be seen in Figure 1, an I2RS client can communicate with 362 multiple I2RS agents. An I2RS client may connect to one or more I2RS 363 agents based upon its needs. Similarly, an I2RS agent may 364 communicate with multiple I2RS clients - whether to respond to their 365 requests, to send notifications, etc. Timely notifications are 366 critical so that several simultaneously operating applications have 367 up-to-date information on the state of the network. 369 As can also be seen in Figure 1, an I2RS Agent may communicate with 370 multiple clients. Each client may send the agent a variety of write 371 operations. In order to keep the protocol simple, two clients should 372 not attempt to write (modify) the same piece of information on an 373 I2RS Agent. This is considered an error. However, such collisions 374 may happen and section 7.8 (multi-headed control) describes how the 375 I2RS agent resolves collision by first utilizing priority to resolve 376 collisions, and second by servicing the requests in a first in, first 377 served basis. The i2rs architecture includes this definition of 378 behavior for this case simply for predictability not because this is 379 an intended result. This predictability will simplify the error 380 handling and suppress oscillations. If additional error cases beyond 381 this simple treatment are required, these error cases should be 382 resolved by the network applications and management systems. 384 In contrast, although multiple I2RS clients may need to supply data 385 into the same list (e.g. a prefix or filter list), this is not 386 considered an error and must be correctly handled. The nuances so 387 that writers do not normally collide should be handled in the 388 information models. 390 The architectural goal for the I2RS is that such errors should 391 produce predictable behaviors, and be reportable to interested 392 clients. The details of the associated policy is discussed in 393 Section 7.8. The same policy mechanism (simple priority per I2RS 394 client) applies to interactions between the I2RS agent and the 395 CLI/SNMP/NETCONF as described in Section 6.3. 397 In addition it must be noted that there may be indirect interactions 398 between write operations. A basic example of this is when two 399 different but overlapping prefixes are written with different 400 forwarding behavior. Detection and avoidance of such interactions is 401 outside the scope of the I2RS work and is left to agent design and 402 implementation. 404 2. Terminology 406 The following terminology is used in this document. 408 agent or I2RS Agent: An I2RS agent provides the supported I2RS 409 services from the local system's routing sub-systems by 410 interacting with the routing element to provide specified 411 behavior. The I2RS agent understands the I2RS protocol and can be 412 contacted by I2RS clients. 414 client or I2RS Client: A client implements the I2RS protocol, uses 415 it to communicate with I2RS Agents, and uses the I2RS services to 416 accomplish a task. It interacts with other elements of the 417 policy, provisioning, and configuration system by means outside of 418 the scope of the I2RS effort. It interacts with the I2RS agents 419 to collect information from the routing and forwarding system. 420 Based on the information and the policy oriented interactions, the 421 I2RS client may also interact with I2RS agents to modify the state 422 of their associated routing systems to achieve operational goals. 423 An I2RS client can be seen as the part of an application that uses 424 and supports I2RS and could be a software library. 426 service or I2RS Service: For the purposes of I2RS, a service refers 427 to a set of related state access functions together with the 428 policies that control their usage. The expectation is that a 429 service will be represented by a data-model. For instance, 'RIB 430 service' could be an example of a service that gives access to 431 state held in a device's RIB. 433 read scope: The read scope of an I2RS client within an I2RS agent 434 is the set of information which the I2RS client is authorized to 435 read within the I2RS agent. The read scope specifies the access 436 restrictions to both see the existence of data and read the value 437 of that data. 439 notification scope: The set of events and associated information 440 that the I2RS Client can request be pushed by the I2RS Agent. 441 I2RS Clients have the ability to register for specific events and 442 information streams, but must be constrained by the access 443 restrictions associated with their notification scope. 445 write scope: The set of field values which the I2RS client is 446 authorized to write (i.e. add, modify or delete). This access can 447 restrict what data can be modified or created, and what specific 448 value sets and ranges can be installed. 450 scope: When unspecified as either read scope, write scope, or 451 notification scope, the term scope applies to the read scope, 452 write scope, and notification scope. 454 resources: A resource is an I2RS-specific use of memory, storage, 455 or execution that a client may consume due to its I2RS operations. 456 The amount of each such resource that a client may consume in the 457 context of a particular agent may be constrained based upon the 458 client's security role. An example of such a resource could 459 include the number of notifications registered for. These are not 460 protocol-specific resources or network-specific resources. 462 role or security role: A security role specifies the scope, 463 resources, priorities, etc. that a client or agent has. If a 464 identity has multiple roles in the security system, the identity 465 is permitted to perform any operations any of those roles permit. 466 Multiple identities may use the same security role. 468 identity: A client is associated with exactly one specific 469 identity. State can be attributed to a particular identity. It 470 is possible for multiple communication channels to use the same 471 identity; in that case, the assumption is that the associated 472 client is coordinating such communication. 474 Identity and scope: A single identity can be associated with 475 multiple roles. Each role has its own scope and an identity 476 associated with multiple roles can use the combined scope of all 477 its roles. More formally, each identity has: 479 a read-scope that is the logical OR of the read-scopes 480 associated with its roles, 482 a write-scope that is the logical OR of the write-scopes 483 associated with its roles, and 485 a notification-scope that is the logical OR of the 486 notification-scopes associated with its roles. 488 secondary identity: An I2RS Client may supply a secondary opaque 489 identity that is not interpreted by the I2RS Agent. An example 490 use is when the I2RS Client is a go-between for multiple 491 applications and it is necessary to track which application has 492 requested a particular operation. 494 Groups: NETCONF Network Access [RFC6536] uses the term group in 495 terms of an Administrative group which supports the well- 496 established distinction between a root account and other types of 497 less-privileged conceptual user accounts. Group still refers to a 498 single identity (e.g. root) which is shared by a group of users. 500 3. Key Architectural Properties 502 Several key architectural properties for the I2RS protocol are 503 elucidated below (simplicity, extensibility, and model-driven 504 programmatic interfaces). However, some architecture properties such 505 as performance and scaling are not described below because they are 506 discussed in [I-D.ietf-i2rs-problem-statement], may may vary based on 507 the particular use-cases. 509 3.1. Simplicity 511 There have been many efforts over the years to improve the access to 512 the information available to the routing and forwarding system. 513 Making such information visible and usable to network management and 514 applications has many well-understood benefits. There are two 515 related challenges in doing so. First, the quantity and diversity of 516 information potentially available is very large. Second, the 517 variation both in the structure of the data and in the kinds of 518 operations required tends to introduce protocol complexity. 520 While the types of operations contemplated here are complex in their 521 nature, it is critical that I2RS be easily deployable and robust. 522 Adding complexity beyond what is needed to satisfy well known and 523 understood requirements would hinder the ease of implementation, the 524 robustness of the protocol, and the deployability of the protocol. 525 Overly complex data models tend to ossify information sets by 526 attempting to describe and close off every possible option, 527 complicating extensibility. 529 Thus, one of the key aims for I2RS is the keep the protocol and 530 modeling architecture simple. So for each architectural component or 531 aspect, we ask ourselves "do we need this complexity, or is the 532 behavior merely nice to have?" Protocol parsimony is clearly a goal. 534 3.2. Extensibility 536 Extensibility of the protocol and data model is very important. In 537 particular, given the necessary scope limitations of the initial 538 work, it is critical that the initial design include strong support 539 for extensibility. 541 The scope of the I2RS work is being restricted in the interests of 542 achieving a deliverable and deployable result. The I2RS Working 543 Group is modeling only a subset of the data of interest. It is 544 clearly desirable for the data models defined in the I2RS to be 545 useful in more general settings. It should be easy to integrate data 546 models from the I2RS with other data. Other work should be able to 547 easily extend it to represent additional aspects of the network 548 elements or network systems. This reinforces the criticality of 549 designing the data models to be highly extensible, preferably in a 550 regular and simple fashion. 552 The I2RS Working Group is defining operations for the I2RS protocol. 553 It would be optimistic to assume that more and different ones may not 554 be needed when the scope of I2RS increases. Thus, it is important to 555 consider extensibility not only of the underlying services' data 556 models, but also of the primitives and protocol operations. 558 3.3. Model-Driven Programmatic Interfaces 560 A critical component of I2RS is the standard information and data 561 models with their associated semantics. While many components of the 562 routing system are standardized, associated data models for them are 563 not yet available. Instead, each router uses different information, 564 different mechanisms, and different CLI which makes a standard 565 interface for use by applications extremely cumbersome to develop and 566 maintain. Well-known data modeling languages exist and may be used 567 for defining the data models for I2RS. 569 There are several key benefits for I2RS in using model-driven 570 architecture and protocol(s). First, it allows for transferring 571 data-models whose content is not explicitly implemented or 572 understood. Second, tools can automate checking and manipulating 573 data; this is particularly valuable for both extensibility and for 574 the ability to easily manipulate and check proprietary data-models. 576 The different services provided by I2RS can correspond to separate 577 data-models. An I2RS agent may indicate which data-models are 578 supported. 580 The purpose of the data model is to provide an definition of the 581 information regarding the routing system that can be used in 582 operational networks. If routing information is being modeled for 583 the first time, a logical information model may be standardized prior 584 to creating the data model. 586 4. Security Considerations 588 This I2RS architecture describes interfaces that clearly require 589 serious consideration of security. As an architecture, I2RS has been 590 designed to re-utilize existing protocols that carry network 591 management information. Two of the existing protocols which the 592 which may be re-used are NETCONF [RFC6241] and RESTCONF 593 [I-D.ietf-netconf-restconf]. The I2RS protocol design process will 594 be to specify additional requirements including security for these 595 existing protocol in order to support the I2RS architecture. After 596 an existing protocol, (e.g. NETCONF or RESTCONF) has been altered to 597 fit the I2RS requirements, then it will be reviewed to determine if 598 it meets the I2RS security requirements. 600 Due to the re-use strategy of the I2RS architecture, this security 601 section describes the assumed security environment for I2RS with 602 additional details on: a) identity and authentication, b) 603 authorization, and c) client redundancy. Each protocol proposed for 604 inclusion as an I2RS protocol will need to be evaluated for the 605 security constraints of the protocol. The detailed requirements for 606 the I2RS protocol and the I2RS security environment will be defined 607 within these global security environments. 609 First, here is a brief description of the assumed security 610 environment for I2RS. The I2RS Agent associated with a Routing 611 Element is a trusted part of that Routing Element. For example, it 612 may be part of a vendor-distributed signed software image for the 613 entire Routing Element or it may be trusted signed application that 614 an operator has installed. The I2RS Agent is assumed to have a 615 separate authentication and authorization channel by which it can 616 validate both the identity and permissions associated with an I2RS 617 Client. To support numerous and speedy interactions between the I2RS 618 Agent and I2RS Client, it is assumed that the I2RS Agent can also 619 cache that particular I2RS Clients are trusted and their associated 620 authorized scope. This implies that the permission information may 621 be old either in a pull model until the I2RS Agent re-requests it, or 622 in a push model until the authentication and authorization channel 623 can notify the I2RS Agent of changes. 625 Mutual authentication between the I2RS Client and I2RS Agent is 626 required. An I2RS Client must be able to trust that the I2RS Agent 627 is attached to the relevant Routing Element so that write/modify 628 operations are correctly applied and so that information received 629 from the I2RS Agent can be trusted by the I2RS Client. 631 An I2RS Client is not automatically trustworthy. Each I2RS Client is 632 associated with identity with a set of scope limitations. 633 Applications using the I2RSS should be aware of the scope limitations 634 of that I2RS Client. If the I2RS Client is acting as a broker for 635 multiple applications, then managing the security, authentication and 636 authorization for that communication is out of scope; nothing 637 prevents the broker from using I2RS protocol and a separate 638 authentication and authorization channel from being used. Regardless 639 of mechanism, an I2RS Client that is acting as a broker is 640 responsible for determining that applications using it are trusted 641 and permitted to make the particular requests. 643 Different levels of integrity, confidentiality, and replay protection 644 are relevant for different aspects of I2RS. The primary 645 communication channel that is used for client authentication and then 646 used by the client to write data requires integrity, confidentiality 647 and replay protection. Appropriate selection of a default required 648 transport protocol is the preferred way of meeting these 649 requirements. 651 Other communications via I2RS may not require integrity, 652 confidentiality, and replay protection. For instance, if an I2RS 653 Client subscribes to an information stream of prefix announcements 654 from OSPF, those may require integrity but probably not 655 confidentiality or replay protection. Similarly, an information 656 stream of interface statistics may not even require guaranteed 657 delivery. In Section 7.2, additional login regarding multiple 658 communication channels and their use is provided. From the security 659 perspective, it is critical to realize that an I2RS Agent may open a 660 new communication channel based upon information provided by an I2RS 661 Client (as described in Section 7.2). For example, an I2RS client 662 may request notifications of certain events and the agent will open a 663 communication channel to report such events. Therefore, to avoid an 664 indirect attack, such a request must be done in the context of an 665 authenticated and authorized client whose communications cannot have 666 been altered. 668 4.1. Identity and Authentication 670 As discussed above, all control exchanges between the I2RS client and 671 agent should be authenticated and integrity protected (such that the 672 contents cannot be changed without detection). Further, manipulation 673 of the system must be accurately attributable. In an ideal 674 architecture, even information collection and notification should be 675 protected; this may be subject to engineering tradeoffs during the 676 design. 678 I2RS clients may be operating on behalf of other applications. While 679 those applications' identities are not needed for authentication or 680 authorization, each application should have a unique opaque 681 identifier that can be provided by the I2RS client to the I2RS agent 682 for purposes of tracking attribution of operations to support 683 functionality such as troubleshooting and logging of network changes. 685 4.2. Authorization 687 All operations using I2RS, both observation and manipulation, should 688 be subject to appropriate authorization controls. Such authorization 689 is based on the identity and assigned role of the I2RS client 690 performing the operations and the I2RS agent in the network element. 691 Multiple Identities may use the same role(s). As noted in the 692 definition of the identity and role above, if multiple roles are 693 associated with an identity then the identity is authorized to 694 perform any operation authorized by any of its roles. 696 I2RS Agents, in performing information collection and manipulation, 697 will be acting on behalf of the I2RS clients. As such, each 698 operation authorization will be based on the lower of the two 699 permissions of the agent itself and of the authenticated client. The 700 mechanism by which this authorization is applied within the device is 701 outside of the scope of I2RS. 703 The appropriate or necessary level of granularity for scope can 704 depend upon the particular I2RS Service and the implementation's 705 granularity. An approach to a similar access control problem is 706 defined in the NetConf Access Control Model (NACM) [RFC6536]; it 707 allows arbitrary access to be specified for a data node instance 708 identifier while defining meaningful manipulable defaults. The 709 identity within NACM [RFC6536] can be specify as either a user name 710 or a group user name (e.g. Root), and this name is linked a scope 711 policy that is contained in a set of access control rules. 712 Similarly, it is expected the I2RS identity links to one role which 713 has a scope policy specified by a set of access control rules. This 714 scope policy can be provided via Local Configuration, exposed as an 715 I2RS Service for manipulation by authorized clients, or via some 716 other method (e.g. AAA service) 718 When an I2RS client is authenticated, its identity is provided to the 719 I2RS Agent, and this identity links to a role which links to the 720 scope policy. Multiple identities may belong to the same role; for 721 example, such a role might be an Internal-Routes-Monitor that allows 722 reading of the portion of the I2RS RIB associated with IP prefixes 723 used for internal device addresses in the AS." 725 4.3. Client Redundancy 727 I2RS must support client redundancy. At the simplest, this can be 728 handled by having a primary and a backup network application that 729 both use the same client identity and can successfully authenticate 730 as such. Since I2RS does not require a continuous transport 731 connection and supports multiple transport sessions, this can provide 732 some basic redundancy. However, it does not address the need for 733 troubleshooting and logging of network changes to be informed about 734 which network application is actually active. At a minimum, basic 735 transport information about each connection and time can be logged 736 with the identity. 738 5. Network Applications and I2RS Client 740 I2RS is expected to be used by network-oriented applications in 741 different architectures. While the interface between a network- 742 oriented application and the I2RS client is outside the scope of 743 I2RS, considering the different architectures is important to 744 sufficiently specify I2RS. 746 In the simplest architecture of direct access, a network-oriented 747 application has an I2RS client as a library or driver for 748 communication with routing elements. 750 In the broker architecture, multiple network-oriented applications 751 communicate in an unspecified fashion to a broker application that 752 contains an I2RS Client. That broker application requires additional 753 functionality for authentication and authorization of the network- 754 oriented applications; such functionality is out of scope for I2RS 755 but similar considerations to those described in Section 4.2 do 756 apply. As discussed in Section 4.1, the broker I2RS Client should 757 determine distinct opaque identifiers for each network-oriented 758 application that is using it. The broker I2RS Client can pass along 759 the appropriate value as a secondary identifier which can be used for 760 tracking attribution of operations. 762 In a third architecture, a routing element or network-oriented 763 application that uses an I2RS Client to access services on a 764 different routing element may also contain an I2RS agent to provide 765 services to other network-oriented applications. However, where the 766 needed information and data models for those services differs from 767 that of a conventional routing element, those models are, at least 768 initially, out of scope for I2RS. Below is an example of such a 769 network application 771 5.1. Example Network Application: Topology Manager 773 A Topology Manager includes an I2RS client that uses the I2RS data 774 models and protocol to collect information about the state of the 775 network by communicating directly with one or more I2RS agents. From 776 these I2RS agents, the Topology Manager collects routing 777 configuration and operational data, such as interface and label- 778 switched path (LSP) information. In addition, the Topology Manager 779 may collect link-state data in several ways - either via I2RS models, 780 by peering with BGP-LS[I-D.ietf-idr-ls-distribution] or listening 781 into the IGP. 783 The set of functionality and collected information that is the 784 Topology Manager may be embedded as a component of a larger 785 application, such as a path computation application. As a stand- 786 alone application, the Topology Manager could be useful to other 787 network applications by providing a coherent picture of the network 788 state accessible via another interface. That interface might use the 789 same I2RS protocol and could provide a topology service using 790 extensions to the I2RS data models. 792 6. I2RS Agent Role and Functionality 794 The I2RS Agent is part of a routing element. As such, it has 795 relationships with that routing element as a whole, and with various 796 components of that routing element. 798 6.1. Relationship to its Routing Element 800 A Routing Element may be implemented with a wide variety of different 801 architectures: an integrated router, a split architecture, 802 distributed architecture, etc. The architecture does not need to 803 affect the general I2RS agent behavior. 805 For scalability and generality, the I2RS agent may be responsible for 806 collecting and delivering large amounts of data from various parts of 807 the routing element. Those parts may or may not actually be part of 808 a single physical device. Thus, for scalability and robustness, it 809 is important that the architecture allow for a distributed set of 810 reporting components providing collected data from the I2RS agent 811 back to the relevant I2RS clients. There may be multiple I2RS Agents 812 within the same router. In such a case, they must have non- 813 overlapping sets of information which they manipulate. 815 To facilitate operations, deployment and troubleshooting, it is 816 important that traceability of the requests received by I2RS Agent's 817 and actions taken be supported via a common data model. 819 6.2. I2RS State Storage 821 State modification requests are sent to the I2RS agent in a routing 822 element by I2RS clients. The I2RS agent is responsible for applying 823 these changes to the system, subject to the authorization discussed 824 above. The I2RS agent will retain knowledge of the changes it has 825 applied, and the client on whose behalf it applied the changes. The 826 I2RS agent will also store active subscriptions. These sets of data 827 form the I2RS data store. This data is retained by the agent until 828 the state is removed by the client, overridden by some other 829 operation such as CLI, or the device reboots. Meaningful logging of 830 the application and removal of changes is recommended. I2RS applied 831 changes to the routing element state will not be retained across 832 routing element reboot. The I2RS data store is not preserved across 833 routing element reboots; thus the I2RS agent will not attempt to 834 reapply such changes after a reboot. 836 6.2.1. I2RS Agent Failure 838 It is expected that an I2RS Agent may fail independently of the 839 associated routing element. This could happen because I2RS is 840 disabled on the routing element or because the I2RS Agent, a separate 841 process or even running on a separate processor, experiences an 842 unexpected failure. Just as routing state learned from a failed 843 source is removed, the ephemeral I2RS state will usually be removed 844 shortly after the failure is detected or as part of a graceful 845 shutdown process. To handle I2RS Agent failure, the I2RS Agent must 846 use two different notifications. 848 NOTIFICATION_I2RS_AGENT_STARTING: This notification identifies that 849 the associated I2RS Agent has started. It includes an agent-boot- 850 count that indicates how many times the I2RS Agent has restarted 851 since the associated routing element restarted. The agent-boot- 852 count allows an I2RS Client to determine if the I2RS Agent has 853 restarted. 855 NOTIFICATION_I2RS_AGENT_TERMINATING: This notification reports that 856 the associated I2RS Agent is shutting down gracefully. Ephemeral 857 state will be removed. It can optionally include a timestamp 858 indicating when the I2RS Agent will shutdown. Use of this 859 timestamp assumes that time synchronization has been done and the 860 timestamp should not have granularity finer than one second 861 because better accuracy of shutdown time is not guaranteed. 863 There are two different failure types that are possible and each has 864 different behavior. 866 Unexpected failure: In this case, the I2RS Agent has unexpectedly 867 crashed and thus cannot notify its clients of anything. Since 868 I2RS does not require a persistent connection between the I2RS 869 Client and I2RS Agent, it is necessary to have a mechanism for the 870 I2RS Agent to notify I2RS Clients that had subscriptions or 871 written ephemeral state; such I2RS Clients should be cached by the 872 I2RS Agent's system in persistent storage. When the I2RS Agent 873 starts, it should send a NOTIFICATION_I2RS_AGENT_STARTING to each 874 cached I2RS Client. 876 Graceful failure: In this case, the I2RS Agent can do specific 877 limited work as part of the process of being disabled. The I2RS 878 Agent must send a NOTIFICATION_I2RS_AGENT_TERMINATING to all its 879 cached I2RS Clients. 881 6.2.2. Starting and Ending 883 When an I2RS client applies changes via the I2RS protocol, those 884 changes are applied and left until removed or the routing element 885 reboots. The network application may make decisions about what to 886 request via I2RS based upon a variety of conditions that imply 887 different start times and stop times. That complexity is managed by 888 the network application and is not handled by I2RS. 890 6.2.3. Reversion 892 An I2RS Agent may decide that some state should no longer be applied. 893 An I2RS Client may instruct an Agent to remove state it has applied. 894 In all such cases, the state will revert to what it would have been 895 without the I2RS client-agent interaction; that state is generally 896 whatever was specified via the CLI, NETCONF, SNMP, etc. I2RS Agents 897 will not store multiple alternative states, nor try to determine 898 which one among such a plurality it should fall back to. Thus, the 899 model followed is not like the RIB, where multiple routes are stored 900 at different preferences. (For I2RS state in the presence of two 901 I2RS clients, please see section 1.2 and section 7.8) 903 An I2RS Client may register for notifications, subject to its 904 notification scope, regarding state modification or removal by a 905 particular I2RS Client. 907 6.3. Interactions with Local Configuration 909 Changes may originate from either Local Configuration or from I2RS. 910 The modifications and data stored by I2RS are separate from the local 911 device configuration, but conflicts between the two must be resolved 912 in a deterministic manner that respects operator-applied policy. 913 That policy can determine whether Local Configuration overrides a 914 particular I2RS client's request or vice versa. To achieve this end, 915 either by default Local Configuration always wins or, optionally, a 916 routing element may permit a priority to be configured on the device 917 for the Local Configuration mechanism. The policy mechanism in the 918 later case is comparing the I2RS client's priority with that priority 919 assigned to the Local Configuration. 921 When the Local Configuration always wins, some communication between 922 that subsystem and the I2RS Agent is still necessary. That 923 communication contains the details of each specific device 924 configuration change that the I2RS Agent is permitted to modify. In 925 addition, when the system determines, that a client's I2RS state is 926 preempted, the I2RS agent must notify the affected I2RS clients; how 927 the system determines this is implementation-dependent. 929 It is critical that policy based upon the source is used because the 930 resolution cannot be time-based. Simply allowing the most recent 931 state to prevail could cause race conditions where the final state is 932 not repeatably deterministic. 934 6.4. Routing Components and Associated I2RS Services 936 For simplicity, each logical protocol or set of functionality that 937 can be compactly described in a separable information and data model 938 is considered as a separate I2RS Service. A routing element need not 939 implement all routing components described nor provide the associated 940 I2RS services. I2RS Services should include a capability model so 941 that peers can determine which parts of the service are supported. 942 Each I2RS Service requires an information model that describes at 943 least the following: data that can be read, data that can be written, 944 notifications that can be subscribed to, and the capability model 945 mentioned above. 947 The initial services included in the I2RS architecture are as 948 follows. 950 *************************** ************** ***************** 951 * I2RS Protocol * * * * Dynamic * 952 * * * Interfaces * * Data & * 953 * +--------+ +-------+ * * * * Statistics * 954 * | Client | | Agent | * ************** ***************** 955 * +--------+ +-------+ * 956 * * ************** ************* 957 *************************** * * * * 958 * Policy * * Base QoS * 959 ******************** ******** * Templates * * Templates * 960 * +--------+ * * * * * ************* 961 * BGP | BGP-LS | * * PIM * ************** 962 * +--------+ * * * 963 ******************** ******** **************************** 964 * MPLS +---------+ +-----+ * 965 ********************************** * | RSVP-TE | | LDP | * 966 * IGPs +------+ +------+ * * +---------+ +-----+ * 967 * +--------+ | OSPF | |IS-IS | * * +--------+ * 968 * | Common | +------+ +------+ * * | Common | * 969 * +--------+ * * +--------+ * 970 ********************************** **************************** 972 ************************************************************** 973 * RIB Manager * 974 * +-------------------+ +---------------+ +------------+ * 975 * | Unicast/multicast | | Policy-Based | | RIB Policy | * 976 * | RIBs & LIBs | | Routing | | Controls | * 977 * | route instances | | (ACLs, etc) | +------------+ * 978 * +-------------------+ +---------------+ * 979 ************************************************************** 981 Figure 2: Anticipated I2RS Services 983 There are relationships between different I2RS Services - whether 984 those be the need for the RIB to refer to specific interfaces, the 985 desire to refer to common complex types (e.g. links, nodes, IP 986 addresses), or the ability to refer to implementation-specific 987 functionality (e.g. pre-defined templates to be applied to interfaces 988 or for QoS behaviors that traffic is direct into). Section 6.4.5 989 discusses information modeling constructs and the range of 990 relationship types that are applicable. 992 6.4.1. Routing and Label Information Bases 994 Routing elements may maintain one or more Information Bases. 995 Examples include Routing Information Bases such as IPv4/IPv6 Unicast 996 or IPv4/IPv6 Multicast. Another such example includes the MPLS Label 997 Information Bases, per-platform or per-interface or per-context. 999 This functionality, exposed via an I2RS Service, must interact 1000 smoothly with the same mechanisms that the routing element already 1001 uses to handle RIB input from multiple sources, so as to safely 1002 change the system state. Conceptually, this can be handled by having 1003 the I2RS Agent communicate with a RIB Manager as a separate routing 1004 source. 1006 The point-to-multipoint state added to the RIB does not need to match 1007 to well-known multicast protocol installed state. The I2RS Agent can 1008 create arbitrary replication state in the RIB, subject to the 1009 advertised capabilities of the routing element. 1011 6.4.2. IGPs, BGP and Multicast Protocols 1013 A separate I2RS Service can expose each routing protocol on the 1014 device. Such I2RS services may include a number of different kinds 1015 of operations: 1017 o reading the various internal RIB(s) of the routing protocol is 1018 often helpful for understanding the state of the network. 1019 Directly writing to these protocol-specific RIBs or databases is 1020 out of scope for I2RS. 1022 o reading the various pieces of policy information the particular 1023 protocol instance is using to drive its operations. 1025 o writing policy information such as interface attributes that are 1026 specific to the routing protocol or BGP policy that may indirectly 1027 manipulate attributes of routes carried in BGP. 1029 o writing routes or prefixes to be advertised via the protocol. 1031 o joining/removing interfaces from the multicast trees 1033 o subscribing to an information stream of route changes 1035 o receiving notifications about peers coming up or going down 1037 For example, the interaction with OSPF might include modifying the 1038 local routing element's link metrics, announcing a locally-attached 1039 prefix, or reading some of the OSPF link-state database. However, 1040 direct modification of the link-state database must not be allowed in 1041 order to preserve network state consistency. 1043 6.4.3. MPLS 1045 I2RS Services will be needed to expose the protocols that create 1046 transport LSPs (e.g. LDP and RSVP-TE) as well as protocols (e.g. 1047 BGP, LDP) that provide MPLS-based services (e.g. pseudowires, L3VPNs, 1048 L2VPNs, etc). This should include all local information about LSPs 1049 originating in, transiting, or terminating in this Routing Element. 1051 6.4.4. Policy and QoS Mechanisms 1053 Many network elements have separate policy and QoS mechanisms, 1054 including knobs which affect local path computation and queue control 1055 capabilities. These capabilities vary widely across implementations, 1056 and I2RS cannot model the full range of information collection or 1057 manipulation of these attributes. A core set does need to be 1058 included in the I2RS information models and supported in the expected 1059 interfaces between the I2RS Agent and the network element, in order 1060 to provide basic capabilities and the hooks for future extensibility. 1062 By taking advantage of extensibility and sub-classing, information 1063 models can specify use of a basic model that can be replaced by a 1064 more detailed model. 1066 6.4.5. Information Modeling, Device Variation, and Information 1067 Relationships 1069 I2RS depends heavily on information models of the relevant aspects of 1070 the Routing Elements to be manipulated. These models drive the data 1071 models and protocol operations for I2RS. It is important that these 1072 information models deal well with a wide variety of actual 1073 implementations of Routing Elements, as seen between different 1074 products and different vendors. There are three ways that I2RS 1075 information models can address these variations: class or type 1076 inheritance, optional features, and templating. 1078 6.4.5.1. Managing Variation: Object Classes/Types and Inheritance 1080 Information modelled by I2RS from a Routing Element can be described 1081 in terms of classes or types or object. Different valid inheritance 1082 definitions can apply. What is appropriate for I2RS to use is not 1083 determined in this architecture; for simplicity, class and subclass 1084 will be used as the example terminology. This I2RS architecture does 1085 require the ability to address variation in Routing Elements by 1086 allowing information models to define parent or base classes and 1087 subclasses. 1089 The base or parent class defines the common aspects that all Routing 1090 Elements are expected to support. Individual subclasses can 1091 represent variations and additional capabilities. When applicable, 1092 there may be several levels of refinement. The I2RS protocol can 1093 then provide mechanisms to allow an I2RS client to determine which 1094 classes a given I2RS Agent has available. Clients which only want 1095 basic capabilities can operate purely in terms of base or parent 1096 classes, while a client needing more details or features can work 1097 with the supported sub-class(es). 1099 As part of I2RS information modeling, clear rules should be specified 1100 for how the parent class and subclass can relate; for example, what 1101 changes can a subclass make to its parent? The description of such 1102 rules should be done so that it can apply across data modeling tools 1103 until the I2RS data modeling language is selected. 1105 6.4.5.2. Managing Variation: Optionality 1107 I2RS Information Models must be clear about what aspects are 1108 optional. For instance, must an instance of a class always contain a 1109 particular data field X? If so, must the client provide a value for 1110 X when creating the object or is there a well-defined default value? 1111 From the Routing Element perspective, in the above example, each 1112 Information model should provide information that: 1114 o Is X required for the data field to be accepted and applied? 1116 o If X is optional, then how does "X" as an optional portion of data 1117 field interact with the required aspects of the data field? 1119 o Does the data field have defaults for the mandatory portion of the 1120 field and the optional portions of the field 1122 o Is X required to be within a particular set of values (e.g. range, 1123 length of strings)? 1125 The information model needs to be clear about what read or write 1126 values are set by client and what responses or actions are required 1127 by the agent. It is important to indicate what is required or 1128 optional in client values and agent responses/actions. 1130 6.4.5.3. Managing Variation: Templating 1132 A template is a collection of information to address a problem; it 1133 cuts across the notions of class and object instances. A template 1134 provides a set of defined values for a set of information fields and 1135 can specify a set of values that must be provided to complete the 1136 template. Further, a flexible template scheme may allow some of the 1137 defined values can be over-written. 1139 For instance, assigning traffic to a particular service class might 1140 be done by specifying a template Queueing with a parameter to 1141 indicate Gold, Silver, or Best Effort. The details of how that is 1142 carried out are not modeled. This does assume that the necessary 1143 templates are made available on the Routing Element via some 1144 mechanism other than I2RS. The idea is that by providing suitable 1145 templates for tasks that need to be accomplished, with templates 1146 implemented differently for different kinds of Routing Elements, the 1147 client can easily interact with the Routing Element without concern 1148 for the variations which are handled by values included in the 1149 template. 1151 If implementation variation can be exposed in other ways, templates 1152 may not be needed. However, templates themselves could be objects 1153 referenced in the protocol messages, with Routing Elements being 1154 configured with the proper templates to complete the operation. This 1155 is a topic for further discussion. 1157 6.4.5.4. Object Relationships 1159 Objects (in a Routing Element or otherwise) do not exist in 1160 isolation. They are related to each other. One of the important 1161 things a class definition does is represent the relationships between 1162 instances of different classes. These relationships can be very 1163 simple, or quite complicated. The following lists the information 1164 relationships that the information models need to support. 1166 6.4.5.4.1. Initialization 1168 The simplest relationship is that one object instance is initialized 1169 by copying another. For example, one may have an object instance 1170 that represents the default setup for a tunnel, and all new tunnels 1171 have fields copied from there if they are not set as part of 1172 establishment. This is closely related to the templates discussed 1173 above, but not identical. Since the relationship is only momentary 1174 it is often not formally represented in modeling, but only captured 1175 in the semantic description of the default object. 1177 6.4.5.4.2. Correlation Identification 1179 Often, it suffices to indicate in one object that it is related to a 1180 second object, without having a strong binding between the two. So 1181 an Identifier is used to represent the relationship. This can be 1182 used to allow for late binding, or a weak binding that does not even 1183 need to exist. A policy name in an object might indicate that if a 1184 policy by that name exists, it is to be applied under some 1185 circumstance. In modeling, this is often represented by the type of 1186 the value. 1188 6.4.5.4.3. Object References 1190 Sometimes the relationship between objects is stronger. A valid ARP 1191 entry has to point to the active interface over which it was derived. 1192 This is the classic meaning of an object reference in programming. 1193 It can be used for relationships like containment or dependence. 1194 This is usually represented by an explicit modeling link. 1196 6.4.5.4.4. Active Reference 1198 There is an even stronger form of coupling between objects if changes 1199 in one of the two objects are always to be reflected in the state of 1200 the other. For example, if a Tunnel has an MTU (maximum transmit 1201 unit), and link MTU changes need to immediately propagate to the 1202 Tunnel MTU, then the tunnel is actively coupled to the link 1203 interface. This kind of active state coupling implies some sort of 1204 internal bookkeeping to ensure consistency, often conceptualized as a 1205 subscription model across objects. 1207 7. I2RS Client Agent Interface 1209 7.1. One Control and Data Exchange Protocol 1211 This I2RS architecture assumes a data-model driven protocol where the 1212 data-models are defined in Yang 1.1 ([RFC6020]), Yang 1.1 1213 ([I-D.ietf-netmod-rfc6020bis]), and associated Yang based model 1214 drafts ([RFC6991], [RFC7223], [RFC7224], [RFC7277], [RFC7317]). Two 1215 the protocols to be expanded to support the I2RS protocol are NETCONF 1216 [RFC6241] and RESTCONF [I-D.ietf-netconf-restconf]. This helps meet 1217 the goal of simplicity and thereby enhances deployability. The I2RS 1218 protocol may need to use several underlying transports (TCP, SCTP 1219 (stream control transport protocol), DCCP (Datagram Congestion 1220 Control Protocol)), with suitable authentication and integrity 1221 protection mechanisms. These different transports can support 1222 different types of communication (e.g. control, reading, 1223 notifications, and information collection) and different sets of 1224 data. Whatever transport is used for the data exchange, it must also 1225 support suitable congestion control mechanisms. The transports 1226 chosen should be operator and implementor friendly to ease adoption. 1228 7.2. Communication Channels 1230 Multiple communication channels and multiple types of communication 1231 channels are required. There may be a range of requirements (e.g. 1232 confidentiality, reliability), and to support the scaling there may 1233 need to be channels originating from multiple sub-components of a 1234 routing element and/or to multiple parts of an I2RS client. All such 1235 communication channels will use the same higher level I2RS protocol. 1237 The use of additional channels for communication will be coordinated 1238 between the I2RS client and the I2RS agent using this protocol. 1240 I2RS protocol communication may be delivered in-band via the routing 1241 system's data plane. I2RS protocol communication might be delivered 1242 out-of-band via a management interface. Depending on what operations 1243 are requested, it is possible for the I2RS protocol communication to 1244 cause the in-band communication channels to stop working; this could 1245 cause the I2RS agent to become unreachable across that communication 1246 channel. 1248 7.3. Capability Negotiation 1250 The support for different protocol capabilities and I2RS Services 1251 will vary across I2RS Clients and Routing Elements supporting I2RS 1252 Agents. Since each I2RS Service is required to include a capability 1253 model (see Section 6.4), negotiation at the protocol level can be 1254 restricted to protocol specifics and which I2RS Services are 1255 supported. 1257 Capability negotiation (such as which transports are supported beyond 1258 the minimum required to implement) will clearly be necessary. It is 1259 important that such negotiations be kept simple and robust, as such 1260 mechanisms are often a source of difficulty in implementation and 1261 deployment. 1263 The protocol capability negotiation can be segmented into the basic 1264 version negotiation (required to ensure basic communication), and the 1265 more complex capability exchange which can take place within the base 1266 protocol mechanisms. In particular, the more complex protocol and 1267 mechanism negotiation can be addressed by defining information models 1268 for both the I2RS Agent and the I2RS Client. These information 1269 models can describe the various capability options. This can then 1270 represent and be used to communicate important information about the 1271 agent, and the capabilities thereof. 1273 7.4. Scope Policy Specifications 1275 As section 4.1 and 4.2 describe, each I2RS Client will have a unique 1276 identity and it may have a secondary identity (see section 2) to aid 1277 in troubleshooting. As section 4 indicates, all authentication and 1278 authorization mechanisms are based on the primary Identity which 1279 links to a role with scope policy for reading data, for writing data, 1280 and limitations on the resources that can be consumed. 1281 Specifications for scope policy need to specify the data and value 1282 ranges for portion of scope policy. 1284 7.5. Connectivity 1286 A client may or may not maintain an active communication channel with 1287 an agent. Therefore, an agent may need to open a communication 1288 channel to the client to communicate previously requested 1289 information. The lack of an active communication channel does not 1290 imply that the associated client is non-functional. When 1291 communication is required, the agent or client can open a new 1292 communication channel. 1294 State held by an agent that is owned by a client should not be 1295 removed or cleaned up when a client is no longer communicating - even 1296 if the agent cannot successfully open a new communication channel to 1297 the client. 1299 For many applications, it may be desirable to clean up state if a 1300 network application dies before removing the state it has created. 1301 Typically, this is dealt with in terms of network application 1302 redundancy. If stronger mechanisms are desired, mechanisms outside 1303 of I2RS may allow a supervisory network application to monitor I2RS 1304 clients, and based on policy known to the supervisor clean up state 1305 if applications die. More complex mechanism instantiated in the I2RS 1306 agent would add complications to the I2RS protocol and are thus left 1307 for future work. 1309 Some examples of such a mechanism include the following. In one 1310 option, the client could request state clean-up if a particular 1311 transport session is terminated. The second is to allow state 1312 expiration, expressed as a policy associated with the I2RS client's 1313 role. The state expiration could occur after there has been no 1314 successful communication channel to or from the I2RS client for the 1315 policy-specified duration. 1317 7.6. Notifications 1319 As with any policy system interacting with the network, the I2RS 1320 Client needs to be able to receive notifications of changes in 1321 network state. Notifications here refers to changes which are 1322 unanticipated, represent events outside the control of the systems 1323 (such as interface failures on controlled devices), or are 1324 sufficiently sparse as to be anomalous in some fashion. A 1325 notification may also be due to a regular event. 1327 Such events may be of interest to multiple I2RS Clients controlling 1328 data handled by an I2RS Agent, and to multiple other I2RS clients 1329 which are collecting information without exerting control. The 1330 architecture therefore requires that it be practical for I2RS Clients 1331 to register for a range of notifications, and for the I2RS Agents to 1332 send notifications to a number of Clients. The I2RS Client should be 1333 able to filter the specific notifications that will be received; the 1334 specific types of events and filtering operations can vary by 1335 information model and need to be specified as part of the information 1336 model. 1338 The I2RS information model needs to include representation of these 1339 events. As discussed earlier, the capability information in the 1340 model will allow I2RS clients to understand which events a given I2RS 1341 Agent is capable of generating. 1343 For performance and scaling by the I2RS client and general 1344 information confidentiality, an I2RS Client needs to be able to 1345 register for just the events it is interested in. It is also 1346 possible that I2RS might provide a stream of notifications via a 1347 publish/subscribe mechanism that is not amenable to having the I2RS 1348 agent do the filtering. 1350 7.7. Information collection 1352 One of the other important aspects of the I2RS is that it is intended 1353 to simplify collecting information about the state of network 1354 elements. This includes both getting a snapshot of a large amount of 1355 data about the current state of the network element, and subscribing 1356 to a feed of the ongoing changes to the set of data or a subset 1357 thereof. This is considered architecturally separate from 1358 notifications due to the differences in information rate and total 1359 volume. 1361 7.8. Multi-Headed Control 1363 As was described earlier, an I2RS Agent interacts with multiple I2RS 1364 Clients who are actively controlling the network element. From an 1365 architecture and design perspective, the assumption is that by means 1366 outside of this system the data to be manipulated within the network 1367 element is appropriately partitioned so that any given piece of 1368 information is only being manipulated by a single I2RS Client. 1370 Nonetheless, unexpected interactions happen and two (or more) I2RS 1371 clients may attempt to manipulate the same piece of data. This is 1372 considered an error case. This architecture does not attempt to 1373 determine what the right state of data should be when such a 1374 collision happens. Rather, the architecture mandates that there be 1375 decidable means by which I2RS Agents handle the collisions. The 1376 mechanism for ensuring predictability is to have a simple priority 1377 associated with each I2RS clients, and the highest priority change 1378 remains in effect. In the case of priority ties, the first client 1379 whose attribution is associated with the data will keep control. 1381 In order for this approach to multi-headed control to be useful for 1382 I2RS Clients, it is important that it is possible for an I2RS Client 1383 to register for changes to any changes made by I2RS to data that it 1384 may care about. This is included in the I2RS event mechanisms. This 1385 also needs to apply to changes made by CLI/NETCONF/SNMP within the 1386 write-scope of the I2RS Agent, as the same priority mechanism (even 1387 if it is "CLI always wins") applies there. The I2RS client may then 1388 respond to the situation as it sees fit. 1390 7.9. Transactions 1392 In the interest of simplicity, the I2RS architecture does not include 1393 multi-message atomicity and rollback mechanisms. Rather, it includes 1394 a small range of error handling for a set of operations included in a 1395 single message. An I2RS Client may indicate one of the following 1396 three error handling for a given message with multiple operations 1397 which it sends to an I2RS Agent: 1399 Perform all or none: This traditional SNMP semantic indicates that 1400 other I2RS agent will keep enough state when handling a single 1401 message to roll back the operations within that message. Either 1402 all the operations will succeed, or none of them will be applied 1403 and an error message will report the single failure which caused 1404 them not to be applied. This is useful when there are, for 1405 example, mutual dependencies across operations in the message. 1407 Perform until error: In this case, the operations in the message 1408 are applied in the specified order. When an error occurs, no 1409 further operations are applied, and an error is returned 1410 indicating the failure. This is useful if there are dependencies 1411 among the operations and they can be topologically sorted. 1413 Perform all storing errors: In this case, the I2RS Agent will 1414 attempt to perform all the operations in the message, and will 1415 return error indications for each one that fails. This is useful 1416 when there is no dependency across the operation, or where the 1417 client would prefer to sort out the effect of errors on its own. 1419 In the interest of robustness and clarity of protocol state, the 1420 protocol will include an explicit reply to modification or write 1421 operations even when they fully succeed. 1423 8. Operational and Manageability Considerations 1425 In order to facilitate troubleshooting of routing elements 1426 implementing I2RS agents, the routing elements should provide for a 1427 mechanism to show actively provisioned I2RS state and other I2RS 1428 Agent internal information. Note that this information may contain 1429 highly sensitive material subject to the Security Considerations of 1430 any data models implemented by that Agent and thus must be protected 1431 according to those considerations. Preferably, this mechanism should 1432 use a different privileged means other than simply connecting as an 1433 I2RS client to learn the data. Using a different mechanism should 1434 improve traceability and failure management. 1436 Manageability plays a key aspect in I2RS. Some initial examples 1437 include: 1439 Resource Limitations: Using I2RS, applications can consume 1440 resources, whether those be operations in a time-frame, entries in 1441 the RIB, stored operations to be triggered, etc. The ability to 1442 set resource limits based upon authorization is important. 1444 Configuration Interactions: The interaction of state installed via 1445 the I2RS and via a router's configuration needs to be clearly 1446 defined. As described in this architecture, a simple priority 1447 that is configured is used to provide sufficient policy 1448 flexibility. 1450 Traceability of Interactions: The ability to trace the interactions 1451 of the requests received by the I2RS Agent's and actions taken by 1452 the I2RS agents is needed so that operations can monitor I2RS 1453 Agents during deployment, and troubleshoot software or network 1454 problems. 1456 Notification Subscription Service: The ability for an I2RS Client to 1457 subscribe to a notification stream pushed from the I2RS Agent 1458 (rather than having I2RS client poll the I2RS agent) provides a 1459 more scalable notification handling for the I2RS Agent-Client 1460 interactions. 1462 9. IANA Considerations 1464 This document includes no request to IANA. 1466 10. Acknowledgements 1468 Significant portions of this draft came from draft-ward-i2rs- 1469 framework-00 and draft-atlas-i2rs-policy-framework-00. 1471 The authors would like to thank Nitin Bahadur, Shane Amante, Ed 1472 Crabbe, Ken Gray, Carlos Pignataro, Wes George, Ron Bonica, Joe 1473 Clarke, Juergen Schoenwalder, Jeff Haas, Jamal Hadi Salim, Scott 1474 Brim, Thomas Narten, Dean Bogdanovic, Tom Petch, Robert Raszuk, 1475 Sriganesh Kini, John Mattsson, Nancy Cam-Winget, DaCheng Zhang, Qin 1476 Wu, Ahmed Abro, Salman Asadullah, Eric Yu, and Deborah Brungard for 1477 their suggestions and review. 1479 11. Informative References 1481 [I-D.ietf-i2rs-problem-statement] 1482 Atlas, A., Nadeau, T., and D. Ward, "Interface to the 1483 Routing System Problem Statement", draft-ietf-i2rs- 1484 problem-statement-08 (work in progress), December 2015. 1486 [I-D.ietf-idr-ls-distribution] 1487 Gredler, H., Medved, J., Previdi, S., Farrel, A., and S. 1488 Ray, "North-Bound Distribution of Link-State and TE 1489 Information using BGP", draft-ietf-idr-ls-distribution-13 1490 (work in progress), October 2015. 1492 [I-D.ietf-netconf-restconf] 1493 Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 1494 Protocol", draft-ietf-netconf-restconf-09 (work in 1495 progress), December 2015. 1497 [I-D.ietf-netmod-rfc6020bis] 1498 Bjorklund, M., "The YANG 1.1 Data Modeling Language", 1499 draft-ietf-netmod-rfc6020bis-09 (work in progress), 1500 December 2015. 1502 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for 1503 the Network Configuration Protocol (NETCONF)", RFC 6020, 1504 DOI 10.17487/RFC6020, October 2010, 1505 . 1507 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 1508 and A. Bierman, Ed., "Network Configuration Protocol 1509 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 1510 . 1512 [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration 1513 Protocol (NETCONF) Access Control Model", RFC 6536, 1514 DOI 10.17487/RFC6536, March 2012, 1515 . 1517 [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", 1518 RFC 6991, DOI 10.17487/RFC6991, July 2013, 1519 . 1521 [RFC7223] Bjorklund, M., "A YANG Data Model for Interface 1522 Management", RFC 7223, DOI 10.17487/RFC7223, May 2014, 1523 . 1525 [RFC7224] Bjorklund, M., "IANA Interface Type YANG Module", 1526 RFC 7224, DOI 10.17487/RFC7224, May 2014, 1527 . 1529 [RFC7277] Bjorklund, M., "A YANG Data Model for IP Management", 1530 RFC 7277, DOI 10.17487/RFC7277, June 2014, 1531 . 1533 [RFC7317] Bierman, A. and M. Bjorklund, "A YANG Data Model for 1534 System Management", RFC 7317, DOI 10.17487/RFC7317, August 1535 2014, . 1537 Authors' Addresses 1539 Alia Atlas 1540 Juniper Networks 1541 10 Technology Park Drive 1542 Westford, MA 01886 1543 USA 1545 Email: akatlas@juniper.net 1547 Joel Halpern 1548 Ericsson 1550 Email: Joel.Halpern@ericsson.com 1552 Susan Hares 1553 Huawei 1555 Email: shares@ndzh.com 1557 Dave Ward 1558 Cisco Systems 1559 Tasman Drive 1560 San Jose, CA 95134 1561 USA 1563 Email: wardd@cisco.com 1565 Thomas D. Nadeau 1566 Brocade 1568 Email: tnadeau@lucidvision.com