Configuring a Layer-2 Ethernet Subinterface

This section describes how to configure a Layer-2 Ethernet subinterface.

Context

Subinterfaces are logical or virtual interfaces created on a physical interface. Subinterfaces share the physical parameters of the physical interface on which they are created. However, subinterfaces have their own data link layer and network layer parameters. A subinterface status change does not affect the main interface status, whereas a main interface status change affects the subinterface status. Subinterfaces work properly only when their main interface is in the Up state.

The device supports creating subinterfaces on Layer-2 Ethernet and Layer-2 Eth-Trunk interfaces. Using a subinterface to terminate a VLAN allows for inter-VLAN forwarding.

Procedure

Access the system view.
```
system-view
```

Access the interface view.

interface interface-type interface-number

Configure a Layer-3 Ethernet interface to work in Layer-2 mode.
```
portswitch
```
Return to the system view.
```
quit
```

Create a subinterface and access the subinterface view.

interface interface-type interface-number.subinterface-number

Configure the encapsulation type for the subinterface and associate a VLAN ID with the subinterface.
```
vlan-type dot1q vlan-id
```
Configure the subinterface as a Layer-2 subinterface.
```
portswitch
```
Add the Layer-2 subinterface to a specific VLAN. You are not advised to add the subinterface to the same VLAN as the interface, which may cause loops in symmetric networking.
```
port default vlan vlan-id
```
Optional: Set the maximum bandwidth for upstream traffic on the interface.
bandwidth ingress bandwidth-number
Optional: Set the maximum bandwidth for downstream traffic on the interface.
bandwidth egress bandwidth-number
Optional: Enable the bypass detection function on the interface.
```
detect-mode tap
```
After bypass detection is enabled, the device detects packets received on this interface and then discards them.
Optional: Configure the automatic interface disabling function based on the session usage.
- In the system view, run the firewall exceeded session enable command to configure the function that the interface is automatically disabled when the session usage reaches the threshold.
- In the system view, run the firewall exceeded session shutdown interface command to configure the list of interfaces that need to be disabled when the session usage reaches the threshold.
- In the system view, run the snmp-agent session trap threshold command to configure the session usage threshold that triggers the interface to be automatically disabled.
Optional: Configure the automatic interface disabling function based on the CPU usage.
- In the system view, run the firewall exceeded cpu-usage enable command to configure the function that the interface is automatically disabled when the CPU usage reaches the threshold.
- In the system view, run the firewall exceeded cpu-usage shutdown interface command to configure the list of interfaces that need to be disabled when the CPU usage reaches the threshold.
- In the system view, run the firewall exceeded cpu-usage threshold command to configure the CPU usage threshold that triggers the interface to be automatically disabled.