Implementations Of Qinq; Modifying The Tpid In A Vlan Tag - HP 6125G Configuration Manual

Figure 50 Single-tagged Ethernet frame header and double-tagged Ethernet frame header
On the other devices in the network, the interfaces may be configured with the MTU of 1500 bytes. The
size of an outer VLAN tag is 4 bytes. HP recommends that you increase the MTU of each interface on the
service provider network to at least 1504 bytes.

Implementations of QinQ

HP 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.

Modifying the TPID in a VLAN tag

A VLAN tag uses the tag protocol identifier (TPID) field to identify the protocol type of the tag. The default
value of this field, as defined in IEEE 802.1Q, is 0x8100.
Figure 51 shows the 802.1Q-defined tag structure of an Ethernet frame.
Figure 51 VLAN tag structure of an Ethernet frame
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