Line Module Forwarding Plane Upgrade

While the applications on the SRP module and the line modules reconstruct themselves, they also begin to build up the new state for the forwarding subsystem. All applications on the line module signal the system when they are ready to start the forwarding upgrade.

Because upgrading the forwarding plane affects forwarding through the chassis for up to 30 seconds on the E120 and E320 routers and about 50 seconds on the ERX-1440 router, unified ISSU does not proceed until the routing protocols have signaled that route reconvergence has completed. Unified ISSU then informs all line modules to simultaneously upgrade their forwarding subsystems.

The line modules then perform the following steps:

1. Halt forwarding through the line modules. Although any links to external devices remain up, incoming data is dropped.
2. Update any changed programmable hardware devices.
3. Update the forwarding subsystem with the new release and upgraded configuration data.
4. Update the routing tables with the reconverged routes.
5. Resume forwarding.

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