3com S7906E Manuel De Montage

 

1-4 

Figure 1-3 VLAN Tag structure of an Ethernet frame 

 

 

An S7900E switch determines whether a received frame is VLAN tagged by comparing its own TPID 

with the TPID field in the received frame. If they match, the frame is considered as a VLAN tagged 

frame. If not, the switch tags the frame with the default VLAN tag of the receiving port. 

The systems of different vendors may set the TPID in the outer VLAN tag of QinQ frames to different 

values. For compatibility with these systems, the S7900E series switches allow you to modify the TPID 

values in the VLAN tags in QinQ frames, including:  

z 

The TPID value in customer network VLAN tags. The switch uses it to determine whether a frame 

received from the customer network is VLAN tagged. If the frame is considered as VLAN untagged, 

the switch tags the frame with the default VLAN tag of the receiving port. This default VLAN tag 

uses the TPID that you have configured. 

z 

The TPID value in service provider network VLAN tags. The switch uses it to determine whether a 

frame received from the service provider network is VLAN tagged. In addition, the switch uses the 

configured TPID in the outer VLAN tag for customer network frames for compatibility with 

third-party devices.  

The TPID in an Ethernet frame has the same position with the protocol type field in a frame without a 

VLAN tag. To avoid problems in packet forwarding and handling in the network, you cannot set the TPID 

value to any of the values in the table below.  

Table 1-1 Reserved protocol type values 

ARP 0x0806 

PUP 0x0200 

RARP 0x8035 

IP 0x0800 

IPv6 0x86DD 

PPPoE 0x8863/0x8864 

MPLS 0x8847/0x8848 

IPX/SPX 0x8137 

IS-IS 0x8000 

LACP 0x8809 

802.1x 0x888E 

Cluster 0x88A7 

Reserved 0xFFFD/0xFFFE/0xFFFF