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Copyright © 2010, Juniper Networks, Inc.
join requests, packet mirroring requests, and so on. Logout requests are cached and
processed at a later stage.
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 5: Configuring a Unified In-Service Software Upgrade
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