3com S7906E Instruccion De Instalación

 

1-3 

Figure 1-2 Single-tagged frame structure vs. double-tagged Ethernet frame structure  

 

 

The default maximum transmission unit (MTU) of an interface is 1500 bytes. The size of an outer VLAN 

tag is 4 bytes. Therefore, you are recommended to increase the MTU of each interface on the service 

provider network. The recommended minimum MTU is 1504 bytes. For how to configure the MTU of an 

interface, refer to Ethernet Port Configuration in the Access Volume. 

 

There are two types of QinQ implementations: basic QinQ and selective QinQ.  

1) Basic 

QinQ 

Basic QinQ is a port-based feature. When a frame arrives at a basic QinQ-enabled port, the port tags it 

with the port’s default VLAN tag, regardless of whether the frame is tagged or untagged. If the received 

frame is already tagged, it becomes a double-tagged frame; if it is untagged, it becomes a frame tagged 

with the port’s default VLAN tag.  

2) Selective 

QinQ 

Selective QinQ is an implementation more flexible than basic QinQ. In addition to all the functions of 

basic QinQ, selective QinQ can tag frames with different outer VLAN tags based on their inner VLAN 

IDs.  

The S7900E series implements selective QinQ by using customer VLAN IDs as match criteria to 

classify frames and then tagging the frames that match a certain VLAN ID with the outer VLAN tag 

defined in the associated traffic behavior.  

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.  

 shows the 802.1Q-defined tag structure of an Ethernet frame.