R3303-HP 6600/HSR6600 Routers Interface Configuration Guide

17
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:
Ste
p
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. 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
p
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.
Enabling fast forwarding on an Ethernet interface
IMPORTANT:
Enabling or disabling fast forwarding on an Ethernet interface of a SAP module restores all confi
g
urations
of the interface to the default.
This feature is supported on only routers configured with SAP modules.
Fast forwarding reduces route lookup time and improves packet forwarding efficiency by performing
hardware forwarding. A router uses the routing table to forward the first packet of a flow. Fast forwarding
creates an entry for the flow and uses the entry to forward subsequent packets of the flow.