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The inefficiencies associated with a polling mechanism like SNMP needed to be removed. Network operators poll periodically because they want the data at regular intervals. So why not just send them the data they want when they want it and skip the overhead of polling? Thus the idea of “streaming” was born. Instead of pulling data off the network, you can sit back and let the network push it for you to a collector.

From Chapter 1, you already know that telemetry is a trend in the industry. Telemetry is a new approach for network monitoring in which data is streamed from network devices continuously using a push model and provides near real-time access to operational statistics. You can precisely define what data you want to subscribe to using standard YANG models, with no CLI required. It allows network devices to continuously stream real-time configuration and operating state information to subscribers. Structured data is published at a defined cadence or on-change, based on the subscription criteria and data type. Telemetry data must be structured in a sensible way to make it easy for monitoring tools to ingest. In other words, good telemetry data must be model based—hence the term data model—driven telemetry, even if everyone uses the term telemetry. The networking industry has converged on YANG as a data modeling language for networking data, making it the natural choice for telemetry. Whether you prefer your data in native, OpenConfig, or IETF YANG models, data model–driven telemetry delivers it to you.

Of course, you want all this data to be easy to use because you know that sooner or later someone will come to your desk and ask for data analytics. Telemetry data needs to be normalized for efficient consumption by Big Data tools. In the software world, encodings such as JSON, protobuf, and XML are widely used to transfer data between software applications. These encodings have an abundance of open source software APIs that make it easy to manipulate and analyze the data.

In terms of protocols, two are possible: the OpenConfig streaming telemetry and the IETF push mechanism. The OpenConfig streaming telemetry uses protobuf as the encoding: The protobuf compact mode is perfectly suited for this, as an efficient encoding (at the cost of managing the .proto files). In the IETF push mechanism, subscriptions are created over existing NETCONF sessions and are developed using XML RPCs. The establish-subscription RPC is sent from a client or collector to the network device.

Model-driven telemetry is your first step in a journey that will transform how you monitor and operate networks. With the power of telemetry, you will discover things you never imagined and will begin to ask more and better questions. More on telemetry can be found in Chapter 6.

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