How to Use Sequential Upgrade in an MX Series Virtual Chassis
Sequential Upgrade Overview
Starting in Junos OS Release 20.1R1, MX Series Virtual Chassis configurations can use sequential upgrade to install new software releases with minimal network downtime. The sequential upgrade process is an alternative to unified in-service software upgrade (ISSU) that installs a new release and reboots each Virtual Chassis member router one at a time. While the upgrade installs on one member router, the other member router continues to operate and handle network operations. This lets you upgrade to a new release with minimal disruption to the network.
Use this document to learn about sequential upgrade, how it works, and how to initiate an sequential upgrade on MX Series Virtual Chassis configurations.
Benefits of Performing a Sequential Upgrade in a MX Series Virtual Chassis
Performing a sequential upgrade in an MX Series Virtual Chassis provides the following benefits:
Upgrades the Junos OS software package while maintaining subscriber sessions
Minimizes network downtime during software image upgrades
Avoids upgrading all Flexible PIC Concentrators (FPCs) and both chassis and at the same time
Sequential upgrade is an alternative to unified ISSU. Compared to ISSU, sequential upgrade offers the following benefits:
Easier troubleshooting. Sequential upgrade applies the upgrade to the backup router first, giving you a window to check on the success of the upgrade and troubleshoot if necessary
Ability to back out of an upgrade. With sequential upgrade, you can issue the
request virtual-chassis upgrade cancelcommand after the backup router is upgraded, giving you the flexibility to back out of an upgrade and roll back to the original software versionLower resource requirements for sequential upgrade
Prerequisites for Performing a Sequential Upgrade in a MX Series Virtual Chassis
Before you start a sequential upgrade in a two-member MX Series Virtual Chassis, make sure you do all of the following:
Ensure that all four Routing Engines in the Virtual Chassis (both Routing Engines in the primary router and both Routing Engines in the backup router) are running the same Junos OS software release.
For minimum traffic disruption, make sure that both member routers are configured with symmetric network interface configurations so traffic can continue to run on all interfaces after switching from the primary router to the backup router.
Ensure that your network is configured to enable moving all traffic from one member router to the other.
Back up the existing router configuration.
Verify that both graceful Routing Engine switchover (GRES) and nonstop active routing (NSR) are enabled.
Disable load throttling with the
set system services resource-monitor no-load-throttlecommand. This will allow subscriber logins during the upgrade process.Download the software release package you want to upgrade to from Juniper’s website at https://support.juniper.net/support/downloads/
Performing a Sequential Upgrade in a MX Series Virtual Chassis
To perform a sequential upgrade in an MX Series Virtual Chassis, follow these steps:
If you want to cancel the sequential upgrade process,
you can issue the request virtual-chassis upgrade cancel command on any Routing Engine after the Virtual Chassis backup router
is updated and before the Virtual Chassis primary router is updated.
After canceling the upgrade process, use the request system software
rollback command to rollback to the previously installed package,
if necessary.
How Sequential Upgrade Works in a MX Series Virtual Chassis
At a high level, the software performs the following
actions after you issue the request virtual-chassis upgrade protocol-backup package-name command to upgrade to a new Junos OS
software release in a two-member Virtual Chassis configuration:
After upgrading the Virtual Chassis backup router, the
next step is to issue the request virtual-chassis upgrade protocol-master package-name command from the backup router CLI
to initiate the upgrade process on Virtual Chassis primary router.
The software performs the same actions as listed in steps 1-7 above,
but for the primary router Routing Engines. After the primary router
Routing Engines reboot, the software performs the following actions:
Switches the role of the Virtual Chassis backup router to become the Virtual Chassis primary router.
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