User's Manual

SME VoIP System Guide, Version 1.5
Proprietary and Confidential
Chapter: VLAN Setup Management
79
An illustration of IEEE 802.1Q VLAN tag in Ethernet frame is as follows:
12.3 How VLAN Switch Work: VLAN Tagging
VLAN functionality can be implemented via explicit frame tagging by switches and end stations.
Network switches and end stations that know about VLANs are said to be VLAN aware. Network
switches and end stations that can interpret VLAN tags are said to be VLAN tag aware. VLAN-tag-
aware switches and end stations add VLAN tags to standard Ethernet frames–a process called
explicit tagging. In explicit tagging, the end station or switch determines the VLAN membership of
a frame and inserts a VLAN tag in the frame header (see figure above for VLAN tagging), so that
downstream link partners can examine just the tag to determine the VLAN membership.
12.4 Implementation Cases
Common types of usage scenarios for VLANs on typical VLAN switches: port-based VLANs,
protocol-based VLANs, and IP subnet-based VLANs. Before figuring out which usage scenario suits
your needs, you must understand what each type of usage scenario implies.
Port-based VLAN: All frames transmitted by a NIC are tagged using only one VLAN ID. The
NIC does not transmit or receive any untagged frames.
All protocols and applications use this virtual interface’s virtual PPA to transmit data traffic.
Therefore all frames transmitted by that NIC port are tagged with the VLAN ID of that
Virtual Interface.
Protocol-based VLAN: The NIC assigns a unique VLAN ID for each Layer 3 protocol (such as
IPv4, IPv6, IPX, and so on). Therefore, the VLAN ID of outbound frames is different for each
protocol. An inbound frame is dropped if the protocol and VLAN ID do not match.
IP subnet-based VLAN: The NIC assigns a unique VLAN ID for each IP subnet it belongs to.
Therefore, the VLAN ID of outbound frames is different for different destination subnets.
An inbound frame is dropped if the IP subnet and VLAN ID do not match.