Configuring Graceful Routing Engine Switchover
This section contains the following topics:
Enabling Graceful Routing Engine Switchover
By default, graceful Routing Engine switchover (GRES)
is disabled. To configure GRES, include the graceful-switchover statement at the [edit chassis redundancy] hierarchy
level.
[edit chassis redundancy] graceful-switchover;
When you enable GRES, the command-line interface (CLI) indicates which Routing Engine you are using. For example:
{master} [edit]
user@host#
To disable GRES, delete the graceful-switchover statement
from the [edit chassis redundancy] hierarchy level.
Configuring Graceful Routing Engine Switchover with Graceful Restart
When using GRES with Graceful Restart, if adjacencies between the Routing Engine and the neighboring peer 'helper' routers time out, graceful restart protocol extensions are unable to notify the peer 'helper' routers about the impending restart. Graceful restart can then stop and cause interruptions in traffic.
To ensure that these adjacencies are kept, change the hold-time for IS-IS protocols from the default of 27 seconds to a value higher than 40 seconds.
Synchronizing the Routing Engine Configuration
A newly inserted backup Routing Engine automatically synchronizes its configuration with the primary Routing Engine configuration.
When you configure GRES, you can bring the backup Routing Engine online after the primary Routing Engine is already running. There is no requirement to start the two Routing Engines simultaneously.
Only when you enable the graceful Routing Engine switchover, you can copy the running Junos OS version of the primary Routing Engine to the backup Routing Engine.
If the system is in ISSU state, you cannot copy the running Junos OS version of the primary Router Engine.
Starting in Junos OS release 14.1, you can enable automatic synchronization of the primary Routing Engine configuration with the backup Routing Engine by including the events CHASSISD_SNMP_TRAP7 statement at the [edit event-options policy policy-name] hierarchy level.
CHASSISD_SNMP_TRAP7 is a system event logging message that the chassis process (chassisd) generates a Simple Network Management Protocol (SNMP) trap with the seven indicated argument-value pairs. An example of an event script to trigger automatic synchronization of primary to the backup Routing Engine is as follows:
[edit event-options]
policy UPGRADE-BACKUPRE {
events CHASSISD_SNMP_TRAP7;
attributes-match {
CHASSISD_SNMP_TRAP7.value5 matches "Routing Engine";
CHASSISD_SNMP_TRAP7.trap matches "Fru Online";
CHASSISD_SNMP_TRAP7.argument5 matches jnxFruName;
}
then {
event-script auto-image-upgrade.slax {
arguments {
trap "{$$.trap}";
value5 "{$$.value5}";
argument5 "{$$.argument5}";
}
}
}
}
event-script {
file auto-image-upgrade.slax;
}After receiving this event, the event policy on the primary Router Engine is triggered and the image available in the /var/sw/pkg path is pushed to the backup Router Engine upgrade. During script execution, the image is copied to the backup Routing Engine's /var/sw/pkg path.
If the image is not available in the /var/sw/pkg path, the script is terminated with an appropriate syslog message.
If the Routing Engine is running at the Junos OS Release 13.2 or later, the Junos automation scripts is synchronized automatically.
After the primary Router Engine is rebooted, the event script available at the /usr/libexec/scripts/event/auto-image-upgrade.slax must be copied to the /var/db/scripts/event path.
For MX Series routers using enhanced subscriber management, the new backup Routing Engine (the former primary Routing Engine) will reboot when a graceful Routing Engine switchover is performed. This cold restart resynchronizes the backup Routing Engine state with that of the new primary Routing Engine, preventing discrepancies in state that might have occurred during the switchover.
Verifying Graceful Routing Engine Switchover Operation
To verify whether GRES is enabled on the backup Routing Engine,
issue the show system switchover command. When the output
of the command indicates that the Graceful switchover field
is set to On, GRES is operational. The status of the kernel
database and configuration database synchronization between Routing
Engines is also provided. For example:
Graceful switchover: On Configuration database: Ready Kernel database: Ready Peer state: Steady state
You must issue the show system switchover command
on the backup Routing Engine. This command is not supported on the
primary Routing Engine.
For more information about the show system switchover command, see the CLI Explorer.