Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual page 93

Chapter 4: Managing Stateful Line Module Switchover
Line module high availability, similar to dual SRP stateful switchover, does not to
prevent the root cause of the reload or restart. This functionality is designed to return
the system to the online, active state as soon as possible. The secondary line module
takes the role of the primary module to preserve subscriber sessions in the up state
with minimal subscriber data outage.
The architecture of line modules supports switchover simultaneously across multiple
1:1 sets of line modules that participate in line module high availability.
Line module high availability is available only on the operational image that runs on
the interface controller (IC). The behavior of the forwarding controller (FC) image, and
the IC boot and diagnostic images provide the same functionality as the behavior that
existed before line module high availability support was implemented.
Line module high availability in a 1:1 redundancy model is supported for ES2 4G LMs
and Service IOAs on E120 and E320 routers. The architecture of line module high
availability ensures that it does not depend on high availability for SRP modules to be
enabled and operational for stateful line module switchover to work. Similarly, any
modifications made to the dual SRP stateful switchover settings do not require or
depend on line module high availability to be enabled and operational.
Unified ISSU is supported on the primary line module in a high availability pair of line
modules. The secondary line module is disabled during the unified ISSU operation and
cold boots after the unified ISSU operation is complete. Line module high availability
mode is active after the secondary line module is up, provided that line module HA
configuration is enabled.
Applications that are configured on the router ensure that their defined settings and
memory requirements are handled on E120 and E320 routers. The primary and
secondary line modules in a high availability pair are determined using the slot
information specified using the mode high-availability slot command in Redundancy
Configuration mode.
Packets that are transmitted between the FC and IC and between the FC and system
controller (SC) are not preserved during a stateful line module recovery.
1:N hot standby mode is not supported for stateful line module switchover. Automatic
switchover of the serial connection to the line module that is designated as the primary
module after switchover is also not supported. Similarly, cold switchover is not
supported if line module high availability is not configured.
Recovery of routers from double failures, such as simultaneous switchover of SRP and
line modules, is not supported. Application-specific statistical details are not retained
across a stateful line module switchover.
Subscriber sessions that constantly move between up and down states are not
maintained across a stateful switchover.
If the line module that contains a downlink interface (connecting to the LAC device)
reloads, owing to hardware or software failures, subscriber sessions are not maintained,
even if the LM and Service IOA are HA-protected. Also, subscriber sessions are not
retained if the line module that connects to the LAC device reloads, when the LM and
Service IOA are part of a redundancy group.
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