HP ProCurve Secure 7000dl Series Basic Management And Configuration Manual page 174

Configuring Ethernet Interfaces
Configure VLAN Support
3-16
Destination Source
address address
6 bytes 6 bytes
Destination Source
address address
6 bytes 6 bytes
Octet 1 Octet 2
Tag protocol ID
(TPID)
Figure 3-3. The 802.1Q Tag
A VLAN is comprised of multiple ports operating as members of the same
subnet (or broadcast domain). Ports on multiple devices can belong to the
same VLAN, and traffic moving between ports in the same VLAN is bridged
(or "switched").
Traffic moving between different VLANs, on the other hand, must be routed.
If a switch supports IP routing, it can internally route IP (IPv4) traffic between
VLANs. If a switch is not configured to route traffic internally between LANs,
an external router must forward traffic between VLANs. The router, of course,
must support 802.1Q. (See Figure 3-4.)
802.1Q Tag Type field Data field
4 bytes 2 bytes Up to 1500 bytes
802.1Q Tag Length Data field
field
4 bytes 2 bytes Up to 1496 bytes
1 2 3 4 5 6 7 8
Octet 4
802.1P VLAN ID
(3 bits) (12 bits)
CRC
Ethernet II with
802.1Q tag
4 bytes
CRC
IEEE 802.3 with
802.1Q tag
4 bytes