Overview
In-Service Software Upgrade (ISSU) provides the ability to upgrade the IOS XR 64-bit version on the routers with minimal disruption on the control plane and forwarding plane. ISSU supports upgrading a Cisco IOS XR 64-bit image from a lower to a higher version. ISSU supports Zero Topology Loss (ZTL) and Minimum Packet Loss (MPL). Packet loss is for less than 50 milliseconds unless specified otherwise in the Release Notes.
SMUs containing software fixes also can be installed using ISSU. See the corresponding SMU Readme for more information on installing the fixes.
You can perform ISSU installation in a single-step or as multi-step processs. However, you must perform the pre-installation tasks before executing ISSU. During the pre-installation tasks and ISSU execution, V1 refers to the image currently running on the router and V2 refers to the upgraded image.
ISSU execution contains the following phases:
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Prepare phase: The installable files are pre-checked and loaded on the router before activation. This phase is optional.
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Activate phase: The new image (V2) is downloaded to all nodes in the router replacing the old image (V1). This phase can be either run in consequent phases like Load, Run, and Cleanup or by using a one-shot Activate phase.
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Commit phase: In this phase, the ISSU installation is committed (complete with V2) on all nodes.
ISSU supports upgrading the System Admin VM and XR VM individually. Using ISSU, the System Admin VM and XR VM can also be upgraded sequentially. The upgrade sequence is System Admin ISSU followed by IOS XR ISSU.
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You cannot upgrade both VMs simultaneously through the ISSU processs. |
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Committing the upgrade from XR VM commits both, the System Admin and XR software. However, committing the upgrade from System Admin VM commits only the System Admin software. |
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When RP1 is the active RP and System Admin VM ISSU is triggered, there is an additional VM switch over compared to performing System Admin VM ISSU from RP0. This is an expected behavior. |