LAN89218AQ Standard Microsystems (SMSC), LAN89218AQ Datasheet - Page 26

• Manufacturer Part Number: LAN89218AQ
• Manufacturer: Standard Microsystems (SMSC)

Specifications of LAN89218AQ

• Lead Free Status / RoHS Status: Compliant

High Performance Single-Chip 10/100 Ethernet Controller for Automotive Applications
Datasheet
3.2.3
Virtual Local Area Network (VLAN) Support
Virtual Local Area Networks or VLANs, as defined within the IEEE 802.3 standard, provide network
administrators one means of grouping nodes within a larger network into broadcast domains. To
implement a VLAN, four extra bytes are added to the basic Ethernet packet. As shown in
Figure 3.1,
"VLAN
Frame", the four bytes are inserted after the Source Address Field and before the Type/Length
field. The first two bytes of the VLAN tag identify the tag, and by convention are set to the value
0x8100. The last two bytes identify the specific VLAN associated with the packet; they also provide a
priority field.
The LAN89218 supports VLAN-tagged packets. The LAN89218 provides two registers which are used
to identify VLAN-tagged packets. One register should normally be set to the conventional VLAN ID of
0x8100. The other register provides a way of identifying VLAN frames tagged with a proprietary (not
0x8100) identifier. If a packet arrives bearing either of these tags in the two bytes succeeding the
Source Address field, the controller will recognize the packet as a VLAN-tagged packet. In this case,
the controller increases the maximum allowed packet size from 1518 to 1522 bytes (normally the
controller filters packets larger than 1518 bytes). This allows the packet to be received, and then
processed by host software, or to be transmitted on the network.
Figure 3.1 VLAN Frame
Revision 1.3 (02-23-10)
26
SMSC LAN89218
DATASHEET