Protocol-Based VLAN 91c CAUTION: You are recommended to set the default VLAN ID of the local Hybridor Trunk ports to the same value as that of the Hybrid or Trunk ports on the peerswitch. Otherwise, packet forwarding may fail on the ports.Protocol-Based VLANIntroduction toProtocol-Based VLANProtocol-based VLAN is also known as protocol VLAN, which is another way toclassify VLANs besides port-based VLAN. Through the protocol-based VLANs, theswitch can analyze the received un-VLAN-tagged packets on the port and matchthe packets with the user-defined protocol template automatically according todifferent encapsulation formats and the values of the special fields. If a packet ismatched, the switch will add a corresponding VLAN tag to it automatically. Thus,the data of the specific protocol is assigned automatically to the correspondingVLAN for transmission.This feature is used for binding the ToS provided in the network to VLAN tofacilitate management and maintenance.Encapsulation Format ofEthernet DataThis section introduces the common encapsulation formats of Ethernet data foryou to understand well the procedure for the switch to identify the packetprotocols.Ethernet II and 802.2/802.3 encapsulationIn the link layer, there are two main packet encapsulation types: Ethernet II and802.2/802.3, whose encapsulation formats are described in the following figures.Ethernet II packet:Figure 28 Ethernet II encapsulation format802.2/802.3 standard packet:Figure 29 802.2/802.3 standard encapsulation formatTable 44 Packet processing of a Hybrid portProcessing of an incoming packetProcessing of an outgoingpacketIf the packet does notcarry a VLAN tagIf the packet carries a VLANtagIf the port is already addedto its default VLAN, add thedefault VLAN tag to thepacket and then forward thepacket.If the port is not added to itsdefault VLAN, discard thepacket.If the VLAN ID is one of theVLAN IDs allowed to passthrough the port, receive thepacket.If the VLAN ID is not one ofthe VLAN IDs allowed to passthrough the port, discard thepacket.Send the packet if the VLANID is allowed to pass throughthe port. Use the port hybridvlan command to configurewhether the port keeps orstrips the tags when sendingpackets of a VLAN (includingthe default VLAN).DA&SA(12) Type(2) DataDA&SA(12) Length(2) DataDSAP(1) SSAP(1) Control(1) OUI(3) PID(2)
