Adjusting The Tpid Values Of Vlan-Vpn Packets - Huawei Quidway S3900 Series Operation Manual

Operation Manual – VLAN VPN
Quidway S3900 Series Ethernet Switches-Release 1510
VLAN tag. If the packet already carries a VLAN tag, the packet becomes a dual-tagged
packet. Otherwise, the packet becomes a packet carrying the default VLAN tag of the
port.

1.1.3 Adjusting the TPID Values of VLAN-VPN Packets

Tag protocol identifier (TPID) is a filed of the VLAN tag. IEEE 802.1Q specifies the
value of TPID to be 0x8100.
Figure 1-3 illustrates the structure of the Tag packet of an Ethernet frame defined by
IEEE 802.1Q.
6 bytes 6 bytes
DA DA DA DA
Figure 1-3 The structure of the Tag packet of an Ethernet frame
S3900 series switches adopt the default value of TPID (Ox8100) defined by the
protocol. Other vendors use other TPID values (such as 0x9100 or 0x9200) in the outer
tags of VLAN-VPN packets.
To be compatible with devices coming from other vendors, S3900 series switches can
adjust the TPID values of VLAN-VPN packets based on ports. You can configure the
TPID value of a port connecting to the public network side by yourself. When the port
forwards a packet, the port will replace the TPID value in the outer VLAN tag of this
packet with the user-defined value. Thus, the VLAN-VPN packets sent to the public
network can be recognized by devices of other vendors.
The position of the TPID field in an Ethernet packet is the same as the position of the
protocol type field in a packet without VLAN Tag. Thus, to avoid confusion happening
when the switch forwards or receives a packet, you must not configure the following
protocol type values listed in Table 1-1 as the TPID value.
Table 1-1 Values of Ethernet frame protocol type in common use
ARP
IP
MPLS
6 bytes 6 bytes 4 bytes 4 bytes
SA SA SA SA
TPID TPID TPID TPID User Priority CFI User Priority CFI User Priority CFI User Priority CFI
2 bytes 2 bytes 2 bytes 2 bytes 3 bits 3 bits 3 bits 3 bits
Protocol type
Huawei Technologies Proprietary
Chapter 1 VLAN-VPN Configuration
46 ~1500 bytes 46 ~1500 bytes
Tag Tag Tag Tag Frame Load Frame Load Frame Load Frame Load
VLAN ID VLAN ID VLAN ID VLAN ID
1bit 1bit 1bit 1bit 12 bits 12 bits 12 bits 12 bits
0x0806
0x0800
0x8847/0x8848
1-2
4 bytes 4 bytes 4 bytes 4 bytes
FCS FCS FCS FCS
Value