About SR Linux

As a Linux-based NOS, SR Linux uses modular applications that are isolated in their own failure domains. A central application manager is responsible for the lifecycle of each application and provides full control of the protocols running on the system.

On SR Linux, each protocol (BGP, IS-IS, and so on) runs as its own application. These applications may be configured using external APIs, including CLI, gNMI, and JSON-RPC. The applications run like any others do in Linux. As well, users can integrate their own applications into SR Linux.

SR Linux uses an unmodified Linux kernel as its foundation to build a suite of network applications. This provides benefits such as reliability, portability, and ease of application development. Using an unmodified kernel also speeds the availability of non-Nokia applications (for example, OpenSSH) and security patches for operating system components.

SR Linux makes extensive use of structured data models. Each application has a YANG model that defines its configuration and state. SR Linux exposes the YANG models to the supported management APIs. For example, the command tree in the CLI is derived from the SR Linux YANG models loaded into the system, and a gNMI client can use Set RPCs to configure an application based on its YANG model. When a configuration is committed, the SR Linux management server validates the YANG models and translates them into protocol buffers for the impart database (IDB).

See the SR Linux architecture overview chapter for more information about the relationship between IDB and SR Linux components).

The SR Linux model-driven management interfaces are based on a common infrastructure that uses YANG models as the core definition for network element configuration, state, and operational actions. The model-driven interfaces take the underlying YANG modules and render them for the particular management interface.

SR Linux supports the following YANG data models:

• Nokia vendor-specific data models

• OpenConfig vendor-neutral data models

SR Linux YANG data models

Each application that SR Linux supports has a Nokia vendor-specific YANG model that defines the application's configuration and state. SR Linux exposes the YANG models to supported management APIs; for example, the CLI command trees derived from the SR Linux YANG models loaded into the system. A gNMI client can use Set RPCs to configure an application based on the YANG model. When you commit a configuration, the SR Linux management server validates the YANG models and translates them into protocol buffers for the impart database (IDB).

OpenConfig data models

OpenConfig is an informal working group that provides structured, vendor-neutral YANG data models to address the use requirements of networking applications and technologies by the community. The OpenConfig data models use standards-based, YANG data-modeling language, support Remote Procedure Calls (RPCs), and allow network operators to use a single set of data models to configure and manage commonly-used network protocols, services, and devices that support the OpenConfig initiative.

Data models interaction

The SR Linux vendor-specific and OpenConfig vendor-neutral data models can be used together to configure and manage network elements. SR Linux data models include vendor-specific features and functions that OpenConfig data models do not describe, and therefore offer a more complete representation of the capabilities of the SR Linux network elements. The SR Linux configuration and operational statements map to path statements in the supported OpenConfig modules. The mappings are exposed in JSON files delivered with the software package.

IDB is a lightweight database that controls messaging between SR Linux applications, using a publish/subscribe (pub/sub) model. To do this, the IDB database is split up into topics. Each application owns a set of topics, to which it publishes information, and can subscribe to topics published by other applications. Applications subscribe to topics when they open a session to the IDB, and publish messages to their own topics for other applications to consume.

IDB stores data as protocol buffers (protobufs). Protobufs are a language-neutral, platform-neutral mechanism for serializing structured data. Each protocol buffer message is a small logical record of information, containing a series of name-value pairs.

SR Linux uses gRPC for inter-process communication. gRPC is a client application that can directly call methods on a server application on a different machine as if it was a local object. The supported external APIs (CLI, gNMI, and JSON-RPC) communicate with the SR Linux and retrieve state information using gRPC.

SR Linux applications share state details with each other using the pub/sub model (see SR Linux infrastructure).

Third-party applications can be fully integrated into the SR Linux with the same functionality as Nokia applications. This includes configuration using YANG, telemetry support, and life-cycle management. Because third-party applications are not managed independently, it allows a reduction in operational overhead.

The SR Linux CLI is itself an application that can load dynamic plugins from other applications. You can develop custom show commands and run them from the SR Linux CLI. The CLI plugins allow for integration with remote systems, supporting retrieval of state information.

SR Linux supports a variety of network chipsets through the Nokia eXtensible Data Path (XDP). XDP serves as a hardware abstraction layer that facilitates adoption of new or non-Nokia network chipsets. It provides a common set of software instructions that northbound applications use so that they are not directly dependent on ASIC vendor SDKs. XDP borrows from the development experience for high-performance VNFs and makes use of user space acceleration for traffic destined for the control plane and any non-ASIC interfaces.

Every SR Linux application, including third-party applications, supports its own YANG model, which can be loaded into the system. Operators can see and define the syntax and semantics of their application in a simple and standardized form. With this design, the YANG data model is defined first, then the CLI, APIs, and show output formats are derived from it.

SR Linux handles management and operations using the gRPC Network Management Interface (gNMI). Because SR Linux is natively model-driven, it can stream telemetry without requiring any translation layers. Telemetry is supported using POLL, ON_CHANGE, and ONCE streaming.

Third-party applications have access to the full streaming telemetry framework. This allows these applications to operate and be monitored, configured, and debugged the same as any other application on the system (see SR Linux software extensibility).

In addition to the gNMI interface, SR Linux includes a CLI and a JSON-RPC API for management. The CLI provides a framework for accessing the underlying data models of the system. The JSON-RPC API interface supports requests against the data models, as well as allowing a programmable interface access to the extensible plugin framework in the CLI.