R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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Figure 14 Traditional Ethernet frame format
IEEE 802.1Q inserts a four-byte VLAN tag after the DA&SA field, as shown in Figure 15.
Figure 15 Position and format of VLAN tag
A VLAN tag comprises the following fields:
• TPID—The 16-bit TPID field with a value of 0x8100 indicates that the frame is VLAN-tagged.
• Priority—The 3-bit priority field indicates the 802.1p priority of the frame.
• CFI—The 1-bit CFI field specifies whether the MAC addresses are encapsulated in the standard
format when packets are transmitted across different media. A value of 0 indicates that MAC
addresses are encapsulated in the standard format; a value of 1 indicates that MAC addresses are
encapsulated in a non-standard format. The value of the field is 0 by default.
• VLAN ID—The 12-bit VLAN ID field identifies the VLAN the frame belongs to. The VLAN ID range
is 0 to 4095. As 0 and 4095 are reserved, a VLAN ID actually ranges from 1 to 4094.
A network device handles an incoming frame depending on whether the frame is VLAN tagged and the
value of the VLAN tag, if any. For more information, see "Introduction to port-based VLAN."
NOTE:
• The Ethernet II encapsulation format is used here. Besides the Ethernet II encapsulation format, Etherne
t
also supports other encapsulation formats, including 802.2 LLC, 802.2 SNAP, and 802.3 raw. The
VLAN tag fields are added to frames encapsulated in these formats for VLAN identification.
• For a frame with multiple VLAN tags, the device handles it according to its outer-most VLAN tag and
transmits its inner VLAN tags as payload.
VLAN types
You can implement VLANs based on the following criteria:
• Port
• MAC address
• Protocol
• IP subnet
• Policy
• Other types, such as voice VLAN
The firewall supports only port-based VLAN.