184
Figure 63
Single-tagged Ethernet frame header and double-tagged Ethernet frame header
The default maximum transmission unit (MTU) of an interface is 1500 bytes. The size of an outer VLAN
tag is 4 bytes. H3C recommends that you increase the MTU of each interface on the service provider
network to at least 1504 bytes. For more information about interface MTU configuration, see
"
Configuring Ethernet interfaces
Implementations of QinQ
H3C provides the following QinQ implementations: basic QinQ and selective QinQ.
•
Basic QinQ
Basic QinQ enables a port to tag any incoming frames with its port VLAN ID (PVID) tag, regardless
of whether they have been tagged or not. If an incoming frame has been tagged, it becomes a
double-tagged frame. If not, it becomes a frame tagged with the PVID tag.
•
Selective QinQ
Selective QinQ is more flexible than basic QinQ. In addition to all the functions of basic QinQ,
selective QinQ enables a port to perform the following per-CVLAN actions for incoming frames:
{
Tag frames from different CVLANs with different SVLAN tags.
{
Mark the outer VLAN 802.1p priority based on the existing inner VLAN 802.1p priority.
{
Modify the inner VLAN ID.
Besides being able to separate the service provider network from the customer networks, selective
QinQ provides abundant service features and enables more flexible networking.
Protocols and standards
IEEE 802.1Q:
IEEE standard for local and metropolitan area networks: Virtual Bridged Local Area
Networks
QinQ configuration task list
When you configure QinQ, follow these guidelines:
•
QinQ requires configurations only on the service provider network.
•
QinQ configurations made in Ethernet interface view take effect on the interface only. Those made
in Layer 2 aggregate interface view take effect on the aggregate interface and all member ports in
the aggregation group. Those made in port group view take effect on all member ports in the port
group.
