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Figure 50 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. Hewlett Packard Enterprise recommends you to increase the MTU of each
interface on the service provider network to at least 1504 bytes.
Implementations of QinQ
Hewlett Packard Enterprise provides the following QinQ implementations: basic QinQ and selective
QinQ.
•
Basic QinQ
Basic QinQ enables a port to tag any incoming frames with its PVID, 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 port's PVID.
•
Selective QinQ (available only on the HPE 3100 v2 EI switches)
Selective QinQ is more flexible than basic QinQ. Selective QinQ enables a port to tag frames
from different CVLANs with different SVLAN tags.
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
value of this field, as defined in IEEE 802.1Q, is 0x8100.
Figure 51 VLAN tag structure of an Ethernet frame
6bytes
DA
TPID
2bytes
The switch determines whether a received frame carries a VLAN tag by checking the TPID value.
For example, if a frame carries a VLAN tag with TPID value 0x8100, but the configured TPID value is
0x9100, the switch considers that the frame does not carry any VLAN tag.
The systems of different vendors might set the TPID of the outer VLAN tag of QinQ frames to
different values. For compatibility with these systems, modify the TPID value so that the QinQ frames,
6bytes
4bytes
SA
VLAN Tag Etype
User Priority
CFI
3bits
1bit
2bytes
46~1500bytes
DATA
VLAN ID
12bits
151
4bytes
FCS
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