Supported Platforms
Split Detection Behavior in a Virtual Chassis
If there is a disruption to a Virtual Chassis configuration for MX Series 3D Universal Edge Routers due to the failure of a member router or one or more Virtual Chassis port interfaces, the resulting connectivity loss can cause a split in the Virtual Chassis configuration. Split detection identifies the split and can minimize further network disruption.
This topic covers:
How Split Detection Works in a Virtual Chassis
Split detection is enabled by default in an MX Series Virtual Chassis. Optionally, you can disable split detection by including the no-split-detection statement at the [edit virtual-chassis] hierarchy level. Disabling split detection can be useful in certain Virtual Chassis configurations.
For example, if the backup router fails in a two-member Virtual Chassis configuration and split detection is enabled (the default behavior), the master router takes a line-card role, and the line cards (FPCs) that do not host Virtual Chassis ports go offline. This state effectively halts routing and disables the Virtual Chassis configuration. By contrast, if the backup router fails in a two-member Virtual Chassis configuration and split detection is disabled, the master router retains mastership and maintains all of the Virtual Chassis ports, effectively resulting in a single-member Virtual Chassis consisting of only the master router.
 | Best Practice: We recommend that you disable split detection for a two-member MX Series Virtual Chassis configuration if you think the backup router is more likely to fail than the Virtual Chassis port interfaces to the backup router. Configuring redundant Virtual Chassis ports on different line cards in each member router reduces the likelihood that all Virtual Chassis port interfaces to the backup router can fail. |
Effect of Split Detection on Virtual Chassis Failure Scenarios
The behavior of a Virtual Chassis during certain failure scenarios depends on whether split detection is enabled or disabled. Table 1 describes the effect of the split detection setting on common failure scenarios in a two-member MX Series Virtual Chassis.
Table 1: Effect of Split Detection on Common Virtual Chassis Failure Scenarios
Type of Failure | Split Detection Setting | Results |
|---|---|---|
Virtual Chassis port interfaces go down | Enabled |
When Virtual Chassis port interfaces are reconnected:
|
Virtual Chassis port interfaces go down | Disabled | When Virtual Chassis port interfaces are disconnected:
When Virtual Chassis port interfaces are reconnected:
|
Virtual Chassis backup router (VC-B) goes down | Enabled |
When the failed router is brought back into service:
|
Virtual Chassis backup router (VC-B) goes down | Disabled |
|
Virtual Chassis master router (VC-M) goes down | Split detection setting has no effect on behavior |
When the original VC-M is brought back into service, or when the original VC-M is replaced with a new router:
|
Active access link between the VC-M and the access node, such as a digital subscriber line access multiplexer (DSLAM), goes down | Split detection setting has no effect on behavior |
|
