Supported Platforms
Related Documentation
Understanding Nonstop Software Upgrade on a Virtual Chassis and Mixed Virtual Chassis
Nonstop software upgrade (NSSU) enables you to upgrade the software running on all member switches in a Virtual Chassis or mixed Virtual Chassis with minimal network traffic disruption during the upgrade. For information on which switches are supported on a mixed Virtual Chassis, see Understanding Mixed EX Series and QFX Series Virtual Chassis or Virtual Chassis Fabric. For information on how to perform a nonstop software upgrade on a Virtual Chassis Fabric, see Understanding Nonstop Software Upgrade on a Virtual Chassis Fabric.
Performing an NSSU provides these benefits:
- No disruption to the control plane—NSSU uses graceful Routing Engine switchover (GRES) to ensure no disruption to the control plane. During the upgrade process, interface, kernel, and routing protocol information is preserved.
- Minimal disruption to network traffic—An NSSU minimizes
network traffic disruption by:
- Upgrading line cards one at a time permits traffic to continue to flow through the line cards that are not being upgraded.
- Upgrading member switches one at a time enables the master and backup to maintain their master and backup roles (although mastership will change) without disruption to traffic.
To achieve minimal disruption to traffic, you must configure link aggregation groups (LAGs) such that the member links of each LAG reside on different line cards or Virtual Chassis members. When one member link of a LAG is down, the remaining links are up, and traffic continues to flow through the LAG.
 | Note: Because NSSU upgrades the software on each line card or on each Virtual Chassis and mixed Virtual Chassis member one at a time, an upgrade using NSSU can take longer than an upgrade using the request system software add command. |
This topic covers:
Requirements for Performing an NSSU
The following requirements apply to Virtual Chassis or mixed Virtual Chassis:
- All Virtual Chassis or mixed Virtual Chassis members and all Routing Engines must be running the same Junos OS release.
- Graceful Routing Engine switchover (GRES) must be enabled.
- For minimal traffic disruption, you must define link aggregation groups (LAGs) such that the member links reside on different Virtual Chassis or mixed Virtual Chassis members or on different line cards.
The following are requirements for Virtual Chassis or mixed Virtual Chassis members:
- The Virtual Chassis or mixed Virtual Chassis members must be connected in a ring topology so that no member is isolated as a result of another member being rebooted. This topology prevents the Virtual Chassis from splitting during an NSSU.
- The Virtual Chassis or mixed Virtual Chassis master and backup must be adjacent to each other in the ring topology. Adjacency permits the master and backup to always be in sync, even when the switches in linecard roles are rebooting.
- The Virtual Chassis or mixed Virtual Chassis must be preprovisioned so that the linecard role has been explicitly assigned to member switches acting in a linecard role. During an NSSU, the Virtual Chassis and mixed Virtual Chassis members must maintain their roles—the master and backup must maintain their master and backup roles (although mastership will change), and the remaining switches must maintain their linecard roles.
- A two-member Virtual Chassis or mixed Virtual Chassis must have no-split-detection configured so that the Virtual Chassis or mixed Virtual Chassis does not split when an NSSU upgrades a member.
How an NSSU Works
This section describes what happens when you request an NSSU on these switches and Virtual Chassis or mixed Virtual Chassis:
Virtual Chassis and Mixed Virtual Chassis
When you request an NSSU on an a Virtual Chassis or mixed Virtual Chassis:
- The Virtual Chassis or mixed Virtual Chassis master verifies
that:
- The backup is online and running the same software version.
- Graceful Routing Engine switchover (GRES) is enabled.
- The Virtual Chassis or mixed Virtual Chassis member has a preprovisioned configuration.
- The master installs the new software image on the backup and reboots it.
- The master resynchronizes the backup.
- The master installs the new software image on member switches that are in the line card role and reboots them, one at a time. The master waits for each member to become online and active before starting the software upgrade on the next member.
- When all members that are in the line card role have been upgraded, the master performs a graceful Routing Engine switchover, and the upgraded backup becomes the master.
- The software on the original master is upgraded and the original master is automatically rebooted. After the original master has rejoined the Virtual Chassis, you can optionally return control to it by requesting a graceful Routing Engine switchover.
NSSU Limitations
You cannot use an NSSU to downgrade the software—that is, to install an earlier version of the software than is currently running on the switch. To install an earlier software version, use the request system software add command.
You cannot roll back to the previous software version after you perform an upgrade using NSSU. If you need to rollback to the previous software version, you can do so by rebooting from the alternate root partition if you have not already copied the new software version into the alternate root partition.
NSSU and Junos OS Release Support
A Virtual Chassis or mixed Virtual Chassis must be running a Junos OS release that supports NSSU before you can perform an NSSU. If a Virtual Chassis or mixed Virtual Chassis is running a software version that does not support NSSU, use the request system software add command. See Understanding Mixed EX Series and QFX Series Virtual Chassis or Virtual Chassis Fabric for information on which switches are supported on a mixed Virtual Chassis.
Overview of NSSU Configuration and Operation
You must ensure that the configuration of the switch or Virtual Chassis meets the requirements described in Requirements for Performing an NSSU. NSSU requires no additional configuration.
You perform an NSSU by executing the request system software nonstop-upgrade command. For detailed instructions on how to perform an NSSU, see the topics in Related Documentation.
