Line Module Arming; Line Module Control Plane Upgrade; Srp Module Switchover - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

Routing protocols The unified ISSU process prompts you to consider raising
the link costs for each routing protocol that is configured on the router. Raising
the link cost for routes through the upgrading router enables neighbors to
recompute better routes to those destinations. If you choose to raise the link
cost, the higher costs can take some time to propagate through the network.
Because the router is unable to determine when this has completed, it waits for
2 minutes before proceeding to the next step in the upgrade.
The reason for raising the link cost is that when the upgrade of the line module
control plane begins, routing protocol updates cannot be installed in the line
modules until that upgrade completes. That period can be in the range 2–15
minutes. During the control plane upgrade, the routing protocols can still accept
new routes and communicate with their neighbors but cannot install the routes.
Unsupported line modules Any unsupported line modules that are present are
held down after the start of this phase when you can no longer gracefully exit
from the unified ISSU process. The modules are held down for the duration of
the unified in-service software upgrade and then undergo a cold boot to the
original running release.
IGMP requests The router cannot handle IGMP requests for channel changing
for IPTV implementations.

Line Module Arming

When the upgrade of the application data on the standby SRP upgrade is completed,
unified ISSU temporarily arms the line modules with the upgrade release in a backup
region of the memory.

Line Module Control Plane Upgrade

At this point, the upgrade release is preserved on each line module in some backup
region. When signaled by the active SRP module, all supported line modules
simultaneously reload and restart with the new release. Forwarding through the
forwarding subsystem on the line modules through the fabric of the system is not
affected by the reload.
The line modules then simultaneously recover any application data preserved in
memory on the line module and upgrade that data into a format that the applications
running on the new release can interpret. This operation can take in the range of
1–10 minutes depending on the size of the data and the upgrade path of the data.
Each line module restores its operational state, running the new release with all data
upgraded to a version acceptable to the new software.
If the upgrade process fails for any line module, that module undergoes a cold restart,
but none of the other line modules is affected.

SRP Module Switchover

At this stage the primary SRP module is running the current release, the redundant
SRP module is running the armed release, and the control plane on each supported
line module is running the armed release.
Chapter 4: Configuring a Unified In-Service Software Upgrade
Unified ISSU Upgrade Phase Overview
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