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How to Use Sequential Upgrade in an MX Series Virtual Chassis
Use this document to learn about sequential upgrade, how it works, and how to initiate an sequential upgrade on MX Series Virtual Chassis configurations.
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.
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 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 cancel command after the backup router is upgraded, giving you the flexibility to back out of an upgrade and roll back to the original software version
Lower 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 master 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 master 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-throttle command. 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/
We do not recommend manually moving the active interface to the backup router. Instead allow the configured LACP failure detection and switchover mechanism to do this when the master router is rebooted during its upgrade procedure.
Performing a Sequential Upgrade in a MX Series Virtual Chassis
To perform a sequential upgrade in an MX Series Virtual Chassis, follow these steps:
- From the Virtual Chassis master router, issue the following
CLI command to initiate the upgrade process on the Virtual Chassis
request virtual-chassis upgrade protocol-backup package-name
Between upgrading the backup router and master router, the statistics for the backup router are not properly displayed on the master router CLI. Statistics for the backup router are available on the backup router CLI.
- After the upgrade finishes on the backup router, issue
the following CLI command from the backup router to begin the same
upgrade process for the Virtual Chassis master router:
request virtual-chassis upgrade protocol-master package-name
You can override the automatic rebooting of Routing Engines by adding the halt-re statement to the CLI command as follows: request virtual-chassis upgrade protocol-backup halt-re package-name. This causes the Routine Engines to halt and wait for the operator to reboot them. Use this command if you want to replace hardware components like FPCs while the router is shut down during the upgrade process.
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 master 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:
- Verifies that an upgrade is not already in progress and exits if an upgrade is already running.
- Validates the software image using existing installation support.
- Performs configuration validation.
- Copies the software image to the backup router Routing Engines.
- Activates the software image on the backup router Routing Engines.
- Reboots the backup router Routing Engines.
- Polls the backup router for FPC interface synchronization after the Routing Engines reboot.
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 master router. The software performs the same actions as listed in steps 1-7 above, but for the master router Routing Engines. After the master router Routing Engines reboot, the software performs the following actions:
- Switches the role of the Virtual Chassis backup router to become the Virtual Chassis master router.
Now that you’ve learned about performing a sequential upgrade in a MX Series Virtual Chassis, you should read up on the unified ISSU process for MX Series Virtual Chassis to decide which upgrade method works best for you. Check out Upgrading Junos OS in an MX Series Virtual Chassis by Performing a Unified ISSU for more information.