1-2Compared with MPLS-based Layer 2 VPN, VLAN-VPN has the following features:z It provides Layer 2 VPN tunnels that are simpler.z VLAN-VPN can be implemented through manual configuration. That is, signaling protocol-relatedconfiguration 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-VPNWith the VLAN-VPN feature enabled, no matter whether or not a received packet already carries aVLAN tag, the switch will tag the received packet with the default VLAN tag of the receiving port and addthe source MAC address to the MAC address table of the default VLAN. When a packet reaches aVLAN-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.Inner-to-Outer Tag Priority Replicating and MappingAs shown in Figure 1-2, the user priority field is the 802.1p priority of the tag. The value of this 3-bit fieldis in the range 0 to 7. By configuring inner-to-outer tag priority replicating or mapping for aVLAN-VPN-enabled port, you can replicate the inner tag priority to the outer tag or assign outer tags ofdifferent priorities to packets according to their inner tag priorities.Figure 1-2 The structure of the VLAN tag in an Ethernet frame0 3115TPID Priority VLAN IDCFIRefer to QoS-QoS Profile part for information about priority.Transparent IGMP Message Transmission on a VLAN-VPN PortFor detailed information about IGMP messages and how a switch processes IGMP messages ofdifferent types, refer to the Multicast module in this manual.For a VLAN-VPN-disabled port, the switch transparently transmits an IGMP message received on theport within the VLAN that the IGMP message belongs to. For the switch to transparently transmit anIGMP message received on a VLAN-VPN port in the outer VLAN, you must enable transparent IGMPmessage transmission on the port.
