H3C Technologies H3C S3600 Series Switches - Manual (Page 1031)

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z It provides Layer 2 VPN tunnels that are simpler.
z VLAN-VPN can be implemented through manual configuration. That is, signaling protocol-related
configuration is not needed.
The VLAN-VPN feature provides you with the following benefits:
z Saves public network VLAN ID resource.
z You can have VLAN IDs of your own, which is independent of public network VLAN IDs.
z 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:
z If the packet already carries a VLAN tag, the packet becomes a dual-tagged packet.
z Otherwise, the packet becomes a packet carrying the default VLAN tag of the port.
Configuring the TPID for VLAN-VPN Packets
A VLAN tag uses the tag protocol identifier (TPID) field to identify the protocol type of the tag. The value
of this field is 0x8100 for IEEE 802.1Q.
Figure 1-2 illustrates the structure of the IEEE 802.1Q VLAN tag in an Ethernet frame.
Figure 1-2 The structure of the VLAN tag in an Ethernet frame
0 31 15
TPID Priority VLAN ID
CFI
An S3600 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.
By default, S3600 series switches adopt the IEEE 802.1Q TPID value 0x8100. Some vendors, however,
use other TPID values such as 0x9100. For compatibility with these systems, the S3600 series switches
allow you to change the TPID that a port uses when tagging a received VLAN-VPN frame as needed.
When doing that, you should set the same TPID on both the customer-side port and the service
provider-side port.
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, you cannot set the TPID value to any
of the values in the table below.
Table 1-1 Commonly used protocol type values in Ethernet frames
Protocol type Value
ARP 0x0806
IP 0x0800
MPLS 0x8847/0x8848