OpenNSL API Guide and Reference Manual: Warm Boot

Warm Boot is the process of restarting the device driver software while the hardware is running without interrupting the data plane. The primary applications for Warm Boot include application software upgrades and driver upgrades. A controlled restart scenario is considered here. During Warm Boot, the OpenNSL driver goes through a special initialization sequence to rebuild its internal state without interfering with switching.

There are two main applications of Warm Boot.

A system vendor may utilize Warm Boot when the control software is upgraded, and where the Switch device software version does not change. In this case, the use of the Warm Boot feature allows for a non-service interrupting restart which greatly minimizes downtime. This is especially important for vendors that have Service Level Agreements with their end customers.
A software upgrade (or downgrade) may be performed on the Switch device software version. In this case, the goal of Warm Boot is to maintain state to the extent possible without interfering with data plane operations.

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