3Com Switch 7750 Configuration Guide Guide

152 CHAPTER 18: QINQ CONFIGURATION
packet already carries a VLAN tag, the packet becomes a dual-tagged packet.
Otherwise, the packet becomes a packet carrying the default VLAN tag of the
port.
Inner-to-Outer Tag
Priority Mapping
As shown in Figure 41, IEEE 802.1Q defines the structure of tagged packets in
Ethernet frames:
Figure 41 The structure of tagged packets of Ethernet frames
The user priority field is the 802.1p priority of the tag. This 3-bit field is in the
range of 0 to 7. Through configuring inner-to-outer tag priority mapping for a
QinQ-enabled port, you can assign different priority for the outer tag of a packet
according to its inner tag priority.
Refer to QoS Manual for the detailed configurations about priority mapping.
QINQ Configuration
Configuration
Prerequisites
Make sure that Voice VLAN is not enabled for the port where QinQ is to be
enabled. The QinQ feature is mutually exclusive with the Voice VLAN feature.
n
BPDU tunnel is a specific application of the QinQ feature. The BPDU tunnel feature
uses the vlan-vpn tunnel command to transmit the customers’ MSTP packets
transparently through the service provider’s network. Refer to MSTP in this
manual.
Configuration Procedure
DA SA Tag Frame Load FCS
6 bytes 6 bytes 4 bytes 46 ~1500 bytes 4 bytes
TPID User Priority CFI VLAN ID
2 bytes 3 bits 1bit 12 bits
DA SA Tag Frame Load FCS
4 bytes
TPID User Priority CFI VLAN ID
2 bytes 3 bits 1bit 12 bits
DA SA Tag Frame Load FCS
6 bytes 6 bytes 4 bytes 46 ~1500 bytes 4 bytes
TPID User Priority CFI VLAN ID
2 bytes 3 bits 1bit 12 bits
DA SA Tag Frame Load FCS
4 bytes
TPID User Priority CFI VLAN ID
2 bytes 3 bits 1bit 12 bits
Tabl e 89 Configure QinQ
Operation Command Description
Enter system view system-view -
Enter Ethernet port view
interface interface-type
interface-number
-
Enable QinQ for the port vlan-vpn enable
Required
By default, QinQ is disabled
on a port.
Configure inner-to-outer tag
priority mapping
vlan-vpn priority
inner-priority remark
outer-priority
Optional