Implementation Of Vlan-Vpn; Adjusting The Tpid Values Of Vlan-Vpn Packets - H3C S5100-SI Operation Manual

The VLAN-VPN feature provides you with the following benefits:
Saves public network VLAN ID resource.
You can have VLAN IDs of your own, which is independent of public network VLAN IDs.
Provides simple Layer 2 VPN solutions for small-sized MANs or intranets.

Implementation of VLAN-VPN

With the VLAN-VPN feature enabled, no matter whether or not a received packet already carries a
VLAN tag, the switch will tag the received packet with the default VLAN tag of the receiving port and add
the source MAC address to the MAC address table of the default VLAN. When a packet reaches a
VLAN-VPN-enabled port:
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.

Adjusting the TPID Values of VLAN-VPN Packets

Tag protocol identifier (TPID) is a field 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.
Figure 1-3 The structure of the Tag packet of an Ethernet frame
0
By default, S5100-SI/EI series switches adopt the TPID value (0x8100) specified in the protocol. Some
vendors use other TPID values (such as 0x9100).
To be compatible with devices coming from other vendors, S5100-SI/EI series switches can adjust the
TPID values of VLAN-VPN packets globally. You can configure TPID values by yourself. When
forwarding packets, the VLAN-VPN uplink port sets the TPID value for outer VLAN tags of these
packets to the user-defined value, so that these packets forwarded to the public network can be
recognized by devices of other manufacturers.
As the position of the TPID field in an Ethernet packet is the same as that of the upper-layer protocol
type field in a packet without VLAN Tag, to avoid confusion in the process of receiving/forwarding a
packet, the TPID value cannot be any of the protocol type value listed in
Table 1-1 Commonly used protocol type values in Ethernet frames
ARP
IP
MPLS
IPX
IS-IS
LACP
15
TPID
Protocol type
Priority VLAN ID
CFI
0x0806
0x0800
0x8847/0x8848
0x8137
0x8000
0x8809
1-2
31
Table 1-1.
Value