Configuring the Preemption Mode

Context

After the interface blocking mode is specified, whether a specified interface will be blocked is determined by the preemption mode. Table 1 lists the preemption modes.

**Table 1** Preemption mode
Preemption Mode		Advantage	Disadvantage
Non-preemption mode		SEP is in non-preemption mode by default. In this mode, blocking an interface does not disconnect any link in a SEP segment.	The blocked interface is one of the two interfaces that complete neighbor negotiations last.
Preemption mode	Delayed preemption	Each time a fault is rectified, the system automatically completes preemption and ensures that the specified interface is blocked.	The delayed preemption mode needs to be specified in advance. There is no default delay in preemption, and the delay time needs to be configured using a command. After delayed preemption is configured successfully, a fault needs to be simulated to ensure that the specified interface is blocked.
Preemption mode	Manual preemption	Whether the specified interface will be blocked can be controlled manually.	The manual preemption mode needs to be specified in advance. After a network fault is rectified and the preemption action is taken, manual preemption no longer takes effect. Manual preemption needs to be configured again to ensure that the blocked point can be moved to the specified point after the next fault is rectified. This increases the maintenance workload.

The following conditions must be met to trigger preemption:

The SEP segment topology is complete.
The primary edge interface or no-neighbor primary edge interface has been elected in the SEP segment.
The function of flexibly specifying a blocked interface is enabled on the device where the primary edge interface or no-neighbor primary edge interface resides.

Perform the following operations on the Layer 2 switching device where the primary edge interface or no-neighbor primary edge interface resides.

Procedure

Run system-view
The system view is displayed.
Run sep segment segment-id
A SEP segment is created and the view of the SEP segment is displayed.
Run preempt { manual | delay seconds }
The preemption mode is configured on the primary edge interface.

By default, no preemption mode is configured on the primary edge interface, that is, the non-preemption mode is used.