Internet Engineering Task Force (IETF) A. Atlas Request for Comments: 7921 Juniper Networks Category: Informational J. Halpern ISSN: 2070-1721 Ericsson S. Hares Huawei D. Ward Cisco Systems T. Nadeau Brocade June 2016 An Architecture for the Interface to the Routing System Abstract This document describes the IETF architecture for a standard, programmatic interface for state transfer in and out of the Internet routing system. It describes the high-level architecture, the building blocks of this high-level architecture, and their interfaces, with particular focus on those to be standardized as part of the Interface to the Routing System (I2RS). Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7921.
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Table of Contents 1. Introduction ....................................................4 1.1. Drivers for the I2RS Architecture ..........................5 1.2. Architectural Overview .....................................6 2. Terminology ....................................................11 3. Key Architectural Properties ...................................13 3.1. Simplicity ................................................13 3.2. Extensibility .............................................14 3.3. Model-Driven Programmatic Interfaces ......................14 4. Security Considerations ........................................15 4.1. Identity and Authentication ...............................17 4.2. Authorization .............................................18 4.3. Client Redundancy .........................................19 4.4. I2RS in Personal Devices ..................................19 5. Network Applications and I2RS Client ...........................19 5.1. Example Network Application: Topology Manager .............20 6. I2RS Agent Role and Functionality ..............................20 6.1. Relationship to Its Routing Element .......................20 6.2. I2RS State Storage ........................................21 6.2.1. I2RS Agent Failure .................................21 6.2.2. Starting and Ending ................................22 6.2.3. Reversion ..........................................23 6.3. Interactions with Local Configuration .....................23 6.3.1. Examples of Local Configuration vs. I2RS Ephemeral Configuration ............................24 6.4. Routing Components and Associated I2RS Services ...........26 6.4.1. Routing and Label Information Bases ................28 6.4.2. IGPs, BGP, and Multicast Protocols .................28 6.4.3. MPLS ...............................................29 6.4.4. Policy and QoS Mechanisms ..........................29 6.4.5. Information Modeling, Device Variation, and Information Relationships ..........................29 188.8.131.52. Managing Variation: Object Classes/Types and Inheritance .............29 184.108.40.206. Managing Variation: Optionality ...........30 220.127.116.11. Managing Variation: Templating ............31 18.104.22.168. Object Relationships ......................31 22.214.171.124.1. Initialization .................31 126.96.36.199.2. Correlation Identification .....32 188.8.131.52.3. Object References ..............32 184.108.40.206.4. Active References ..............32 7. I2RS Client Agent Interface ....................................32 7.1. One Control and Data Exchange Protocol ....................32 7.2. Communication Channels ....................................33 7.3. Capability Negotiation ....................................33 7.4. Scope Policy Specifications ...............................34 7.5. Connectivity ..............................................34
7.6. Notifications .............................................35 7.7. Information Collection ....................................35 7.8. Multi-headed Control ......................................36 7.9. Transactions ..............................................36 8. Operational and Manageability Considerations ...................37 9. References .....................................................38 9.1. Normative References ......................................38 9.2. Informative References ....................................38 Acknowledgements ..................................................39 Authors' Addresses ................................................40 1. Introduction Routers that form the Internet routing infrastructure maintain state at various layers of detail and function. For example, a typical router maintains a Routing Information Base (RIB) and implements routing protocols such as OSPF, IS-IS, and BGP to exchange reachability information, topology information, protocol state, and other information about the state of the network with other routers. Routers convert all of this information into forwarding entries, which are then used to forward packets and flows between network elements. The forwarding plane and the specified forwarding entries then contain active state information that describes the expected and observed operational behavior of the router and that is also needed by the network applications. Network-oriented applications require easy access to this information to learn the network topology, to verify that programmed state is installed in the forwarding plane, to measure the behavior of various flows, routes or forwarding entries, as well as to understand the configured and active states of the router. Network-oriented applications also require easy access to an interface, which will allow them to program and control state related to forwarding. This document sets out an architecture for a common, standards-based interface to this information. This Interface to the Routing System (I2RS) facilitates control and observation of the routing-related state (for example, a Routing Element RIB manager's state), as well as enabling network-oriented applications to be built on top of today's routed networks. The I2RS is a programmatic asynchronous interface for transferring state into and out of the Internet routing system. This I2RS architecture recognizes that the routing system and a router's Operating System (OS) provide useful mechanisms that applications could harness to accomplish application-level goals. These network-oriented applications can leverage the I2RS programmatic interface to create new ways to combine retrieving Internet routing data, analyzing this data, and setting state within routers.
Fundamental to I2RS are clear data models that define the semantics of the information that can be written and read. I2RS provides a way for applications to customize network behavior while leveraging the existing routing system as desired. I2RS provides a framework for applications (including controller applications) to register and to request the appropriate information for each particular application. Although the I2RS architecture is general enough to support information and data models for a variety of data, and aspects of the I2RS solution may be useful in domains other than routing, I2RS and this document are specifically focused on an interface for routing data. Security is a concern for any new I2RS. Section 4 provides an overview of the security considerations for the I2RS architecture. The detailed requirements for I2RS protocol security are contained in [I2RS-PROT-SEC], and the detailed security requirements for environment in which the I2RS protocol exists are contained in [I2RS-ENV-SEC]. 1.1. Drivers for the I2RS Architecture There are four key drivers that shape the I2RS architecture. First is the need for an interface that is programmatic and asynchronous and that offers fast, interactive access for atomic operations. Second is the access to structured information and state that is frequently not directly configurable or modeled in existing implementations or configuration protocols. Third is the ability to subscribe to structured, filterable event notifications from the router. Fourth, the operation of I2RS is to be data-model-driven to facilitate extensibility and provide standard data models to be used by network applications. I2RS is described as an asynchronous programmatic interface, the key properties of which are described in Section 5 of [RFC7920]. The I2RS architecture facilitates obtaining information from the router. The I2RS architecture provides the ability to not only read specific information, but also to subscribe to targeted information streams, filtered events, and thresholded events. Such an interface also facilitates the injection of ephemeral state into the routing system. Ephemeral state on a router is the state that does not survive the reboot of a routing device or the reboot of the software handling the I2RS software on a routing device. A non- routing protocol or application could inject state into a routing element via the state-insertion functionality of I2RS and that state could then be distributed in a routing or signaling protocol and/or
be used locally (e.g., to program the co-located forwarding plane). I2RS will only permit modification of state that would be possible to modify via Local Configuration; no direct manipulation of protocol- internal, dynamically determined data is envisioned. 1.2. Architectural Overview Figure 1 shows the basic architecture for I2RS between applications using I2RS, their associated I2RS clients, and I2RS agents. Applications access I2RS services through I2RS clients. A single I2RS client can provide access to one or more applications. This figure also shows the types of data models associated with the routing system (dynamic configuration, static configuration, Local Configuration, and routing and signaling configuration) that the I2RS agent data models may access or augment. Figure 1 is similar to Figure 1 in [RFC7920], but the figure in this document shows additional detail on how the applications utilize I2RS clients to interact with I2RS agents. It also shows a logical view of the data models associated with the routing system rather than a functional view (RIB, Forwarding Information Base (FIB), topology, policy, routing/signaling protocols, etc.) In Figure 1, Clients A and B each provide access to a single application (Applications A and B, respectively), while Client P provides access to multiple applications. Applications can access I2RS services through local or remote clients. A local client operates on the same physical box as the routing system. In contrast, a remote client operates across the network. In the figure, Applications A and B access I2RS services through local clients, while Applications C, D, and E access I2RS services through a remote client. The details of how applications communicate with a remote client is out of scope for I2RS. An I2RS client can access one or more I2RS agents. In Figure 1, Clients B and P access I2RS agents 1 and 2. Likewise, an I2RS agent can provide service to one or more clients. In this figure, I2RS agent 1 provides services to Clients A, B, and P while Agent 2 provides services to only Clients B and P. I2RS agents and clients communicate with one another using an asynchronous protocol. Therefore, a single client can post multiple simultaneous requests, either to a single agent or to multiple agents. Furthermore, an agent can process multiple requests, either from a single client or from multiple clients, simultaneously.
The I2RS agent provides read and write access to selected data on the routing element that are organized into I2RS services. Section 4 describes how access is mediated by authentication and access control mechanisms. Figure 1 shows I2RS agents being able to write ephemeral static state (e.g., RIB entries) and to read from dynamic static (e.g., MPLS Label Switched Path Identifier (LSP-ID) or number of active BGP peers). In addition to read and write access, the I2RS agent allows clients to subscribe to different types of notifications about events affecting different object instances. One example of a notification of such an event (which is unrelated to an object creation, modification or deletion) is when a next hop in the RIB is resolved in a way that allows it to be used by a RIB manager for installation in the forwarding plane as part of a particular route. Please see Sections 7.6 and 7.7 for details. The scope of I2RS is to define the interactions between the I2RS agent and the I2RS client and the associated proper behavior of the I2RS agent and I2RS client.
****************** ***************** ***************** * Application C * * Application D * * Application E * ****************** ***************** ***************** ^ ^ ^ |--------------| | |--------------| | | | v v v *************** * Client P * *************** ^ ^ | |-------------------------| *********************** | *********************** | * Application A * | * Application B * | * * | * * | * +----------------+ * | * +----------------+ * | * | Client A | * | * | Client B | * | * +----------------+ * | * +----------------+ * | ******* ^ ************* | ***** ^ ****** ^ ****** | | | | | | | |-------------| | | |-----| | | -----------------------| | | | | | | | ************ v * v * v ********* ***************** v * v ******** * +---------------------+ * * +---------------------+ * * | Agent 1 | * * | Agent 2 | * * +---------------------+ * * +---------------------+ * * ^ ^ ^ ^ * * ^ ^ ^ ^ * * | | | | * * | | | | * * v | | v * * v | | v * * +---------+ | | +--------+ * * +---------+ | | +--------+ * * | Routing | | | | Local | * * | Routing | | | | Local | * * | and | | | | Config | * * | and | | | | Config | * * |Signaling| | | +--------+ * * |Signaling| | | +--------+ * * +---------+ | | ^ * * +---------+ | | ^ * * ^ | | | * * ^ | | | * * | |----| | | * * | |----| | | * * v | v v * * v | v v * * +----------+ +------------+ * * +----------+ +------------+ * * | Dynamic | | Static | * * | Dynamic | | Static | * * | System | | System | * * | System | | System | * * | State | | State | * * | State | | State | * * +----------+ +------------+ * * +----------+ +------------+ * * * * * * Routing Element 1 * * Routing Element 2 * ******************************** ******************************** Figure 1: Architecture of I2RS Clients and Agents
Routing Element: A Routing Element implements some subset of the routing system. It does not need to have a forwarding plane associated with it. Examples of Routing Elements can include: * A router with a forwarding plane and RIB Manager that runs IS-IS, OSPF, BGP, PIM, etc., * A BGP speaker acting as a Route Reflector, * A Label Switching Router (LSR) that implements RSVP-TE, OSPF-TE, and the Path Computation Element (PCE) Communication Protocol (PCEP) and has a forwarding plane and associated RIB Manager, and * A server that runs IS-IS, OSPF, and BGP and uses Forwarding and Control Element Separation (ForCES) to control a remote forwarding plane. A Routing Element may be locally managed, whether via command-line interface (CLI), SNMP, or the Network Configuration Protocol (NETCONF). Routing and Signaling: This block represents that portion of the Routing Element that implements part of the Internet routing system. It includes not merely standardized protocols (i.e., IS-IS, OSPF, BGP, PIM, RSVP-TE, LDP, etc.), but also the RIB Manager layer. Local Configuration: The black box behavior for interactions between the ephemeral state that I2RS installs into the routing element; Local Configuration is defined by this document and the behaviors specified by the I2RS protocol. Dynamic System State: An I2RS agent needs access to state on a routing element beyond what is contained in the routing subsystem. Such state may include various counters, statistics, flow data, and local events. This is the subset of operational state that is needed by network applications based on I2RS that is not contained in the routing and signaling information. How this information is provided to the I2RS agent is out of scope, but the standardized information and data models for what is exposed are part of I2RS. Static System State: An I2RS agent needs access to static state on a routing element beyond what is contained in the routing subsystem. An example of such state is specifying queueing behavior for an interface or traffic. How the I2RS agent modifies or obtains this information is out of scope, but the standardized information and data models for what is exposed are part of I2RS.
I2RS agent: See the definition in Section 2. Application: A network application that needs to observe the network or manipulate the network to achieve its service requirements. I2RS client: See the definition in Section 2. As can be seen in Figure 1, an I2RS client can communicate with multiple I2RS agents. Similarly, an I2RS agent may communicate with multiple I2RS clients -- whether to respond to their requests, to send notifications, etc. Timely notifications are critical so that several simultaneously operating applications have up-to-date information on the state of the network. As can also be seen in Figure 1, an I2RS agent may communicate with multiple clients. Each client may send the agent a variety of write operations. In order to keep the protocol simple, two clients should not attempt to write (modify) the same piece of information on an I2RS agent. This is considered an error. However, such collisions may happen and Section 7.8 ("Multi-headed Control") describes how the I2RS agent resolves collision by first utilizing priority to resolve collisions and second by servicing the requests in a first-in, first- served basis. The I2RS architecture includes this definition of behavior for this case simply for predictability, not because this is an intended result. This predictability will simplify error handling and suppress oscillations. If additional error cases beyond this simple treatment are required, these error cases should be resolved by the network applications and management systems. In contrast, although multiple I2RS clients may need to supply data into the same list (e.g., a prefix or filter list), this is not considered an error and must be correctly handled. The nuances so that writers do not normally collide should be handled in the information models. The architectural goal for I2RS is that such errors should produce predictable behaviors and be reportable to interested clients. The details of the associated policy is discussed in Section 7.8. The same policy mechanism (simple priority per I2RS client) applies to interactions between the I2RS agent and the CLI/SNMP/NETCONF as described in Section 6.3. In addition, it must be noted that there may be indirect interactions between write operations. A basic example of this is when two different but overlapping prefixes are written with different forwarding behavior. Detection and avoidance of such interactions is outside the scope of the I2RS work and is left to agent design and implementation.
2. Terminology The following terminology is used in this document. agent or I2RS agent: An I2RS agent provides the supported I2RS services from the local system's routing subsystems by interacting with the routing element to provide specified behavior. The I2RS agent understands the I2RS protocol and can be contacted by I2RS clients. client or I2RS client: A client implements the I2RS protocol, uses it to communicate with I2RS agents, and uses the I2RS services to accomplish a task. It interacts with other elements of the policy, provisioning, and configuration system by means outside of the scope of the I2RS effort. It interacts with the I2RS agents to collect information from the routing and forwarding system. Based on the information and the policy-oriented interactions, the I2RS client may also interact with I2RS agents to modify the state of their associated routing systems to achieve operational goals. An I2RS client can be seen as the part of an application that uses and supports I2RS and could be a software library. service or I2RS service: For the purposes of I2RS, a service refers to a set of related state access functions together with the policies that control their usage. The expectation is that a service will be represented by a data model. For instance, 'RIB service' could be an example of a service that gives access to state held in a device's RIB. read scope: The read scope of an I2RS client within an I2RS agent is the set of information that the I2RS client is authorized to read within the I2RS agent. The read scope specifies the access restrictions to both see the existence of data and read the value of that data. notification scope: The notification scope is the set of events and associated information that the I2RS client can request be pushed by the I2RS agent. I2RS clients have the ability to register for specific events and information streams, but must be constrained by the access restrictions associated with their notification scope. write scope: The write scope is the set of field values that the I2RS client is authorized to write (i.e., add, modify or delete). This access can restrict what data can be modified or created, and what specific value sets and ranges can be installed.
scope: When unspecified as either read scope, write scope, or notification scope, the term "scope" applies to the read scope, write scope, and notification scope. resources: A resource is an I2RS-specific use of memory, storage, or execution that a client may consume due to its I2RS operations. The amount of each such resource that a client may consume in the context of a particular agent may be constrained based upon the client's security role. An example of such a resource could include the number of notifications registered for. These are not protocol-specific resources or network-specific resources. role or security role: A security role specifies the scope, resources, priorities, etc., that a client or agent has. If an identity has multiple roles in the security system, the identity is permitted to perform any operations any of those roles permit. Multiple identities may use the same security role. identity: A client is associated with exactly one specific identity. State can be attributed to a particular identity. It is possible for multiple communication channels to use the same identity; in that case, the assumption is that the associated client is coordinating such communication. identity and scope: A single identity can be associated with multiple roles. Each role has its own scope, and an identity associated with multiple roles can use the combined scope of all its roles. More formally, each identity has: * a read scope that is the logical OR of the read scopes associated with its roles, * a write scope that is the logical OR of the write scopes associated with its roles, and * a notification scope that is the logical OR of the notification scopes associated with its roles. secondary identity: An I2RS client may supply a secondary opaque identifier for a secondary identity that is not interpreted by the I2RS agent. An example of the use of the secondary opaque identifier is when the I2RS client is a go-between for multiple applications and it is necessary to track which application has requested a particular operation.
ephemeral data: Ephemeral data is data that does not persist across a reboot (software or hardware) or a power on/off condition. Ephemeral data can be configured data or data recorded from operations of the router. Ephemeral configuration data also has the property that a system cannot roll back to a previous ephemeral configuration state. group: The NETCONF Access Control Model [RFC6536] uses the term "group" in terms of an administrative group that supports the well-established distinction between a root account and other types of less-privileged conceptual user accounts. "Group" still refers to a single identity (e.g., root) that is shared by a group of users. routing system/subsystem: A routing system or subsystem is a set of software and/or hardware that determines where packets are forwarded. The I2RS agent is a component of a routing system. The term "packets" may be qualified to be layer 1 frames, layer 2 frames, or layer 3 packets. The phrase "Internet routing system" implies the packets that have IP as layer 3. A routing "subsystem" indicates that the routing software/hardware is only the subsystem of another larger system. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Key Architectural Properties Several key architectural properties for the I2RS protocol are elucidated below (simplicity, extensibility, and model-driven programmatic interfaces). However, some architectural properties such as performance and scaling are not described below because they are discussed in [RFC7920] and because they may vary based on the particular use cases. 3.1. Simplicity There have been many efforts over the years to improve access to the information available to the routing and forwarding system. Making such information visible and usable to network management and applications has many well-understood benefits. There are two related challenges in doing so. First, the quantity and diversity of information potentially available is very large. Second, the variation both in the structure of the data and in the kinds of operations required tends to introduce protocol complexity.
While the types of operations contemplated here are complex in their nature, it is critical that I2RS be easily deployable and robust. Adding complexity beyond what is needed to satisfy well known and understood requirements would hinder the ease of implementation, the robustness of the protocol, and the deployability of the protocol. Overly complex data models tend to ossify information sets by attempting to describe and close off every possible option, complicating extensibility. Thus, one of the key aims for I2RS is to keep the protocol and modeling architecture simple. So for each architectural component or aspect, we ask ourselves, "Do we need this complexity, or is the behavior merely nice to have?" If we need the complexity, we should ask ourselves, "Is this the simplest way to provide this complexity in the I2RS external interface?" 3.2. Extensibility Extensibility of the protocol and data model is very important. In particular, given the necessary scope limitations of the initial work, it is critical that the initial design include strong support for extensibility. The scope of I2RS work is being designed in phases to provide deliverable and deployable results at every phase. Each phase will have a specific set of requirements, and the I2RS protocol and data models will progress toward these requirements. Therefore, it is clearly desirable for the I2RS data models to be easily and highly extensible to represent additional aspects of the network elements or network systems. It should be easy to integrate data models from I2RS with other data. This reinforces the criticality of designing the data models to be highly extensible, preferably in a regular and simple fashion. The I2RS Working Group is defining operations for the I2RS protocol. It would be optimistic to assume that more and different ones may not be needed when the scope of I2RS increases. Thus, it is important to consider extensibility not only of the underlying services' data models, but also of the primitives and protocol operations. 3.3. Model-Driven Programmatic Interfaces A critical component of I2RS is the standard information and data models with their associated semantics. While many components of the routing system are standardized, associated data models for them are not yet available. Instead, each router uses different information, different mechanisms, and different CLI, which makes a standard interface for use by applications extremely cumbersome to develop and
maintain. Well-known data modeling languages exist and may be used for defining the data models for I2RS. There are several key benefits for I2RS in using model-driven architecture and protocol(s). First, it allows for data-model- focused processing of management data that provides modular implementation in I2RS clients and I2RS agents. The I2RS client only needs to implement the models the I2RS client is able to access. The I2RS agent only needs to implement the data models the I2RS agent supports. Second, tools can automate checking and manipulating data; this is particularly valuable for both extensibility and for the ability to easily manipulate and check proprietary data models. The different services provided by I2RS can correspond to separate data models. An I2RS agent may indicate which data models are supported. The purpose of the data model is to provide a definition of the information regarding the routing system that can be used in operational networks. If routing information is being modeled for the first time, a logical information model may be standardized prior to creating the data model. 4. Security Considerations This I2RS architecture describes interfaces that clearly require serious consideration of security. As an architecture, I2RS has been designed to reuse existing protocols that carry network management information. Two of the existing protocols that are being reused for the I2RS protocol version 1 are NETCONF [RFC6241] and RESTCONF [RESTCONF]. Additional protocols may be reused in future versions of the I2RS protocol. The I2RS protocol design process will be to specify additional requirements (including security) for the existing protocols in order in order to support the I2RS architecture. After an existing protocol (e.g., NETCONF or RESTCONF) has been altered to fit the I2RS requirements, then it will be reviewed to determine if it meets these requirements. During this review of changes to existing protocols to serve the I2RS architecture, an in-depth security review of the revised protocol should be done. Due to the reuse strategy of the I2RS architecture, this security section describes the assumed security environment for I2RS with additional details on a) identity and authentication, b) authorization, and c) client redundancy. Each protocol proposed for
inclusion as an I2RS protocol will need to be evaluated for the security constraints of the protocol. The detailed requirements for the I2RS protocol and the I2RS security environment will be defined within these global security environments. The I2RS protocol security requirements for I2RS protocol version 1 are contained in [I2RS-PROT-SEC], and the global I2RS security environment requirements are contained [I2RS-ENV-SEC]. First, here is a brief description of the assumed security environment for I2RS. The I2RS agent associated with a Routing Element is a trusted part of that Routing Element. For example, it may be part of a vendor-distributed signed software image for the entire Routing Element, or it may be a trusted signed application that an operator has installed. The I2RS agent is assumed to have a separate authentication and authorization channel by which it can validate both the identity and permissions associated with an I2RS client. To support numerous and speedy interactions between the I2RS agent and I2RS client, it is assumed that the I2RS agent can also cache that particular I2RS clients are trusted and their associated authorized scope. This implies that the permission information may be old either in a pull model until the I2RS agent re-requests it or in a push model until the authentication and authorization channel can notify the I2RS agent of changes. Mutual authentication between the I2RS client and I2RS agent is required. An I2RS client must be able to trust that the I2RS agent is attached to the relevant Routing Element so that write/modify operations are correctly applied and so that information received from the I2RS agent can be trusted by the I2RS client. An I2RS client is not automatically trustworthy. Each I2RS client is associated with an identity with a set of scope limitations. Applications using an I2RS client should be aware that the scope limitations of an I2RS client are based on its identity (see Section 4.1) and the assigned role that the identity has. A role sets specific authorization limits on the actions that an I2RS client can successfully request of an I2RS agent (see Section 4.2). For example, one I2RS client may only be able to read a static route table, but another client may be able add an ephemeral route to the static route table. If the I2RS client is acting as a broker for multiple applications, then managing the security, authentication, and authorization for that communication is out of scope; nothing prevents the broker from using the I2RS protocol and a separate authentication and authorization channel from being used. Regardless of the mechanism, an I2RS client that is acting as a broker is responsible for
determining that applications using it are trusted and permitted to make the particular requests. Different levels of integrity, confidentiality, and replay protection are relevant for different aspects of I2RS. The primary communication channel that is used for client authentication and then used by the client to write data requires integrity, confidentiality and replay protection. Appropriate selection of a default required transport protocol is the preferred way of meeting these requirements. Other communications via I2RS may not require integrity, confidentiality, and replay protection. For instance, if an I2RS client subscribes to an information stream of prefix announcements from OSPF, those may require integrity but probably not confidentiality or replay protection. Similarly, an information stream of interface statistics may not even require guaranteed delivery. In Section 7.2, additional logins regarding multiple communication channels and their use is provided. From the security perspective, it is critical to realize that an I2RS agent may open a new communication channel based upon information provided by an I2RS client (as described in Section 7.2). For example, an I2RS client may request notifications of certain events, and the agent will open a communication channel to report such events. Therefore, to avoid an indirect attack, such a request must be done in the context of an authenticated and authorized client whose communications cannot have been altered. 4.1. Identity and Authentication As discussed above, all control exchanges between the I2RS client and agent should be authenticated and integrity-protected (such that the contents cannot be changed without detection). Further, manipulation of the system must be accurately attributable. In an ideal architecture, even information collection and notification should be protected; this may be subject to engineering trade-offs during the design. I2RS clients may be operating on behalf of other applications. While those applications' identities are not needed for authentication or authorization, each application should have a unique opaque identifier that can be provided by the I2RS client to the I2RS agent for purposes of tracking attribution of operations to an application identifier (and from that to the application's identity). This tracking of operations to an application supports I2RS functionality for tracing actions (to aid troubleshooting in routers) and logging of network changes.
4.2. Authorization All operations using I2RS, both observation and manipulation, should be subject to appropriate authorization controls. Such authorization is based on the identity and assigned role of the I2RS client performing the operations and the I2RS agent in the network element. Multiple identities may use the same role(s). As noted in the definitions of "identity" and "role" above, if multiple roles are associated with an identity then the identity is authorized to perform any operation authorized by any of its roles. I2RS agents, in performing information collection and manipulation, will be acting on behalf of the I2RS clients. As such, each operation authorization will be based on the lower of the two permissions of the agent itself and of the authenticated client. The mechanism by which this authorization is applied within the device is outside of the scope of I2RS. The appropriate or necessary level of granularity for scope can depend upon the particular I2RS service and the implementation's granularity. An approach to a similar access control problem is defined in the NETCONF Access Control Model (NACM) [RFC6536]; it allows arbitrary access to be specified for a data node instance identifier while defining meaningful manipulable defaults. The identity within NACM [RFC6536] can be specified as either a user name or a group user name (e.g., Root), and this name is linked a scope policy that is contained in a set of access control rules. Similarly, it is expected the I2RS identity links to one role that has a scope policy specified by a set of access control rules. This scope policy can be provided via Local Configuration, exposed as an I2RS service for manipulation by authorized clients, or via some other method (e.g., Authentication, Authorization, and Accounting (AAA) service) While the I2RS agent allows access based on the I2RS client's scope policy, this does not mean the access is required to arrive on a particular transport connection or from a particular I2RS client by the I2RS architecture. The operator-applied scope policy may or may not restrict the transport connection or the identities that can access a local I2RS agent. When an I2RS client is authenticated, its identity is provided to the I2RS agent, and this identity links to a role that links to the scope policy. Multiple identities may belong to the same role; for example, such a role might be an Internal-Routes-Monitor that allows reading of the portion of the I2RS RIB associated with IP prefixes used for internal device addresses in the AS.
4.3. Client Redundancy I2RS must support client redundancy. At the simplest, this can be handled by having a primary and a backup network application that both use the same client identity and can successfully authenticate as such. Since I2RS does not require a continuous transport connection and supports multiple transport sessions, this can provide some basic redundancy. However, it does not address the need for troubleshooting and logging of network changes to be informed about which network application is actually active. At a minimum, basic transport information about each connection and time can be logged with the identity. 4.4. I2RS in Personal Devices If an I2RS agent or I2RS client is tightly correlated with a person (such as if an I2RS agent is running on someone's phone to control tethering), then this usage can raise privacy issues, over and above the security issues that normally need to be handled in I2RS. One example of an I2RS interaction that could raise privacy issues is if the I2RS interaction enabled easier location tracking of a person's phone. The I2RS protocol and data models should consider if privacy issues can arise when clients or agents are used for such use cases. 5. Network Applications and I2RS Client I2RS is expected to be used by network-oriented applications in different architectures. While the interface between a network- oriented application and the I2RS client is outside the scope of I2RS, considering the different architectures is important to sufficiently specify I2RS. In the simplest architecture of direct access, a network-oriented application has an I2RS client as a library or driver for communication with routing elements. In the broker architecture, multiple network-oriented applications communicate in an unspecified fashion to a broker application that contains an I2RS client. That broker application requires additional functionality for authentication and authorization of the network- oriented applications; such functionality is out of scope for I2RS, but similar considerations to those described in Section 4.2 do apply. As discussed in Section 4.1, the broker I2RS client should determine distinct opaque identifiers for each network-oriented application that is using it. The broker I2RS client can pass along the appropriate value as a secondary identifier, which can be used for tracking attribution of operations.
In a third architecture, a routing element or network-oriented application that uses an I2RS client to access services on a different routing element may also contain an I2RS agent to provide services to other network-oriented applications. However, where the needed information and data models for those services differs from that of a conventional routing element, those models are, at least initially, out of scope for I2RS. The following section describes an example of such a network application. 5.1. Example Network Application: Topology Manager A Topology Manager includes an I2RS client that uses the I2RS data models and protocol to collect information about the state of the network by communicating directly with one or more I2RS agents. From these I2RS agents, the Topology Manager collects routing configuration and operational data, such as interface and Label Switched Path (LSP) information. In addition, the Topology Manager may collect link-state data in several ways -- via I2RS models, by peering with BGP-LS [RFC7752], or by listening into the IGP. The set of functionality and collected information that is the Topology Manager may be embedded as a component of a larger application, such as a path computation application. As a stand- alone application, the Topology Manager could be useful to other network applications by providing a coherent picture of the network state accessible via another interface. That interface might use the same I2RS protocol and could provide a topology service using extensions to the I2RS data models.