(Optional) Configuring the Function of Mirroring Packet Content of a Specified Length

Specify the length of packet content to be mirrored to reduce the bandwidth to be consumed by the observing port and improve service performance.

Before you configure this function, configure a mirrored port and an observing port.

**Table 1** Interfaces supporting local mirroring
Interface Type	Mirrored Port	Observing Port
Layer 3 Ethernet main interfaces (including Eth-Trunk interfaces and a Layer 3 main interface configured as a BAS main interface)	Supported	Supported
BAS interface	Supported NOTE: When a VE interface functions as a BAS interface, local flow mirroring is supported only on the access VE interface in hardware loopback mode.	Not supported
Ethernet sub-interfaces (including Eth-Trunk interfaces)	Supported NOTE: After a sub-interface is configured as a dot1q, dot1q VLAN tag termination, QinQ VLAN tag termination, EVC, or BAS sub-interface, the sub-interface still supports mirroring.	Supported NOTE: After a sub-interface is configured as a dot1q VLAN tag termination, QinQ VLAN tag termination, or BAS sub-interface, the sub-interface does not support be configured as an observing port. The observing port can only be configured on the EVC sub-interface with untag or dot1q traffic encapsulation type.

Enter the system view.
system-view
For a mirrored port that is not an EVC Layer 2 sub-interface, enter the interface view.
interface interface-type interface-number
For a Layer 2 sub-interface or BD functioning as a mirrored port, run either of the following commands:
- For a common mirrored port, run the interface interface-type interface-number.subnum mode l2 command to enter the EVC Layer 2 sub-interface view.
- For a mirrored port configured in mirroring instance mode, run the mirror instance instance-name location command to enter the mirroring instance view.
Configure the mirrored port to mirror packet content based on a specified length.
port-mirroring slice-size slice-size-value