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Taking the M120 Host Subsystem Offline
The host subsystem is taken offline and brought online as a unit. Before you replace a CB or a Routing Engine, you must take the host subsystem offline.
Normally, if two host subsystems are installed in the router, RE0 functions as the master and RE1 functions as the backup. You can remove the backup host subsystem (or either of its components) without interrupting the functioning of the router. If you take the master host subsystem offline, the backup host subsystem becomes the master (the router might reboot, depending on your configuration). If the router has only one host subsystem, taking the host subsystem offline causes the router to shut down.
Table 1 explains the effect of taking the host subsystem offline.
Table 1: Effect of Taking the M120 Host Subsystem Offline
Type of Host Subsystem | Effect of taking the Host Subsystem Offline |
|---|---|
Nonredundant host subsystem | The router shuts down. |
Backup host subsystem | The functioning of the router is not interrupted. The backup host subsystem is hot-removable and hot-insertable. |
Master host subsystem | The backup host subsystem becomes the master. The backup Routing Engine assumes Routing Engine functions. The master host subsystem is hot-pluggable. Removal or failure of the master Routing Engine affects forwarding and routing based on the high availability configuration:
|
 | Note: Router performance might change if the backup Routing Engine's configuration differs from the former master's configuration. For the most predictable performance, configure the two Routing Engines identically, except for parameters unique to each Routing Engine. |
| Note: For information about configuring graceful Routing Engine switchover, graceful restart, and nonstop active routing, see the Junos OS High Availability Configuration Guide. |
| Note: The first supported release for graceful Routing Engine switchover and nonstop active routing on the M120 router is Junos OS Release 8.2 and Junos OS Release 9.0, respectively. Graceful restart software requirements are dependent on the routing protocols configured on the router. For the minimum software requirements for graceful restart, see the Junos OS High Availability Configuration Guide. |
To take a host subsystem offline:
- Determine whether the host subsystem is functioning
as the master or as the backup, using one of the two following methods:
- Check the Routing Engine LEDs on the craft interface. If the green RE MASTER LED is lit, the corresponding host subsystem is functioning as the master.
- The master Routing Engine is designated Master in the Current state field when you issue the command:
user@host> show chassis routing-engineRouting Engine status: Slot 0: Current state Master ...
- If the host subsystem is functioning as
the master, switch it to backup using the CLI command:
user@host> request chassis routing-engine master switch - On the console or other management device connected to
the Routing Engine that is paired with the CB you are removing, enter
CLI operational mode and issue the following command. The command
shuts down the Routing Engine cleanly, so its state information is
preserved:
user@host> request system haltWait until a message appears on the console confirming that the operating system has halted.
For more information about the command, see the Junos OS System Basics and Services Command Reference.
Note: The FEB might continue forwarding traffic for approximately 5 minutes after the request system halt command has been issued.
