R2511-HP MSR Router Series Interface Configuration Guide(V5)

Configuring a Layer 3 Ethernet interface or

subinterface

Setting the MTU for an Ethernet interface or subinterface

The value of Maximum Transmission Unit (MTU) affects the fragmentation and re-assembly of IP packets.

To set the MTU for an Ethernet interface or subinterface:

Step Command Remarks

1. Enter system view.

system-view N/A

2. Enter Ethernet interface

or subinterface view.

interface interface-type { interface-number |

interface-number.subnumber }

N/A

3. Set the MTU.

mtu size The default setting is 1500.

Due to the QoS queue length limit (for example, the default length of an FIFO queue is 75), too small an

MTU will result in too many fragments, which will be discarded from the QoS queue. You can increase

MTU or QoS queue length correctly. In Ethernet interface view, you can use the qos fifo queue-length

command to change the QoS queue length. For more information, see ACL and QoS Configuration

Guide.

Configuring an Ethernet interface to operate in promiscuous

mode

An Ethernet interface usually receives only packets with matched destination MAC addresses. After you

configure an Ethernet interface to operate in promiscuous mode, however, the interface no longer checks

the MAC addresses in received packets. Rather, it receives all Ethernet packets with correct format. You

might need to configure a network listening port to operate in promiscuous mode.

To configure an Ethernet interface to operate in promiscuous mode:

Ste

Command

Remarks

1. Enter system view.

system-view N/A

2. Enter Ethernet interface view.

interface interface-type

interface-number

N/A

3. Configure the Ethernet

interface to operate in

promiscuous mode.

promiscuous

By default, an Ethernet interface does

not operate in promiscuous mode.

Configuring the MAC address of an Ethernet interface or

subinterface

When a Layer 3 Ethernet subinterface is created, it uses the MAC address of its host interface by default.

As a result, all Layer 3 Ethernet subinterfaces of a Layer 3 Ethernet interface share the same MAC address.