Stateful Line Module Switchover Overview

JunosE Software now supports high availability for ES2 4G line modules configured with Service IOAs on E120 and E320 routers. These line modules function in a 1:1 redundancy mode with the active module as the primary line module and the spare or standby module as the secondary line module. This functionality of high availability for line modules is also referred to as stateful line module switchover.

In releases in which the stateful line module switchover feature was not supported or in scenarios in which this behavior is disabled, the restart of a line module causes it to be reloaded and all the subscriber sessions that are routed through it to be disconnected. All users connected to the router when the line module is reloading need to log in again and reestablish their connections. Based on the router models deployed in your environment, the configuration settings applied in your network, and the number of active subscriber sessions, reestablishment and resetting of subscriber connections can consume several minutes.

Stateful line module switchover reduces the impact on subscriber traffic during a stateful switchover from the active line module to the standby line module by ensuring that existing subscriber sessions remain active with a brief disconnection in traffic. Stateful line module switchover maintains user sessions and reduces data traffic outage through the router to a brief duration during the switchover, thereby improving the overall availability of the router. Stateful line module switchover keeps the connections through the module up, with a brief disruption in forwarding on existing interfaces through the fabric slice. When you restart the line module, applications recover to a stable state by synchronizing with their peers on the SRP module swiftly to resume normal operations. This mechanism enables the system to keep user connections up and data forwarding outage minimal through the fabric slice.