Juniper ERX - RELEASE 11.1.X HARDWARE GUIDE 03-23-2010 Hardware Manual page 115

Chapter 9: Troubleshooting
Figure 49: SRP Module LEDs
NOTE: The primary SRP module illuminates the REDUNDANT LED only when the
SRP module detects a secondary or standby SRP module online. The standby SRP
module monitors an activity signal from the primary SRP module to determine its
state; it does not shadow the operations of the primary SRP module.
If the standby SRP module detects that the primary SRP module is not active (and
high-availability mode is not enabled), it reboots the system and takes control. If
high-availability mode has been enabled, automatic switchover occurs with near
hitless failover. (ERX7xx and ERX14xx models only)
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Understanding Status LEDs to Troubleshoot