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Disabling Split and Merge in a Virtual Chassis

The split and merge feature is enabled by default on all EX Series switches and QFX Series devices that are connected into a Virtual Chassis.

If a Virtual Chassis splits:

  • Each part detects the members they can still reach and elects a new primary for those members to form a smaller Virtual Chassis.

  • Each part determines if it will remain the active new configuration of the original Virtual Chassis. The feature’s rules ensure only one part remains active after a split.

See Understanding Split and Merge in a Virtual Chassis for complete details on what happens during a Virtual Chassis split or merge.

You can disable the split and merge feature in a Virtual Chassis by configuring the no-split-detection option on the Virtual Chassis. In this case, if the Virtual Chassis splits, both parts of the split Virtual Chassis configuration usually remain active.

However, with split detection disabled, be aware that the two resulting Virtual Chassis might not form as you might expect. For example, in a preprovisioned Virtual Chassis:

  • If both of the Routing Engines end up in the same Virtual Chassis configuration after a split, the other part of the split Virtual Chassis configuration can’t form and remains inactive (because it has no members that can take on the primary or backup Routing Engine).

  • If the Routing Engines end up in different parts of the split Virtual Chassis configuration and the rest of the member switches are configured in linecard roles, then the resulting Virtual Chassis parts might not be able to select a backup Routing Engine.

Best Practice:

We generally recommend that you:

  • Keep the default setting with the split and merge feature enabled for any Virtual Chassis with more than two members.

    This provides the most predictable results when a split happens, and enables the split and merge feature to perform a merge after the issues that caused the split are resolved.

  • Disable split and merge on a Virtual Chassis with only two member switches by setting the no-split-detection option.

    We have found that a two-member switch Virtual Chassis with split and merge disabled re-forms more quickly with fewer complications when a split occurs.

    If you expand a two-member Virtual Chassis to include more members, you should delete the no-split-detection setting to re-enable split and merge feature again.

To disable the split and merge feature in a Virtual Chassis:

To remove this configuration item to restore the default configuration with the split and merge feature again (recommended when a two-member Virtual Chassis is expanded to have more members):