3Com 8807 Configuration Manual page 848

848 C 76: Q Q C
HAPTER IN
Implementation of QinQ
Adjusting TPID Values of
QinQ Packets
ONFIGURATION
QinQ can be implemented on Switch 8800 Family series switches in the following
ways:
1 Enabling VLAN VPN on ports
With VLAN VPN enabled, a received packet is tagged with the default VLAN tag of
the port no matter whether or not the packet carries a VLAN tag. Otherwise, the
packet is transmitted with the default VLAN tag carried.
2 Configuring traffic classification-based nested VLANs
You can implement QinQ in a more flexible way by configuring traffic
classification-based nested VLANs. You can specify to perform the following
operations on packets that match specified ACL rules:
Setting the outer VLAN tags
■
Modifying the outer VLAN tags
■
Tag protocol identifier (TPID) is a portion of the VLAN tag field. IEEE 802.1Q
specifies the value of TPID to be 0x8100.
The structure of the Tag field of an Ethernet frame defined by IEEE 802.1Q is as
follows:
Figure 198 The structure of the Tag field of an Ethernet frame
6 bytes 6 bytes
DA DA DA DA
TPID TPID TPID TPID
2 bytes 2 bytes 2 bytes 2 bytes
By default, a Switch 8800 Family series switch uses 0x8100 as the value of the
TPID field, which is defined by IEEE 802.1Q. But Switch 8800 Family series
switches can also adjust the TPID values of QinQ packets. This ensures Switch
8800 Family series switches are compatible with devices coming from other
vendors even through the later use other TPID values (such as 0x9100 or 0x9200)
in the outer tags of QinQ packets.
To modify the TPID values of packets, you need to set the ports connecting to the
public networks to be VLAN-VPN uplink ports, whose TPID value can be
configured by users. After you configure a TPID value for a VLAN-VPN uplink port,
the switch substitutes the new TPID values for those VLAN-VPN uplink ports in the
outer tags carried by received packets before transmitting the packet through the
VLAN-VPN uplink ports to enable these packets to be accepted by devices of other
vendors.
6 bytes 6 bytes 4 bytes 4 bytes
SA SA SA SA Tag Tag Tag Tag
User Priority CFI User Priority CFI User Priority CFI User Priority CFI
3 bits 3 bits 3 bits 3 bits 1bit 1bit 1bit 1bit
46 ˜1500 bytes 46 ˜1500 bytes
Frame Load Frame Load Frame Load Frame Load
VLAN ID VLAN ID VLAN ID VLAN ID
12 bits 12 bits 12 bits 12 bits
4 bytes 4 bytes 4 bytes 4 bytes
FCS FCS FCS FCS