ZyXEL Communications GS-2750, User Manual

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Chapter 21 VLAN Stacking
GS-2750 User’s Guide
163
21.3 VLAN Tag Format
A VLAN tag (service provider VLAN stacking or customer IEEE 802.1Q) consists of the
following three fields.
Type is a standard Ethernet type code identifying the frame and indicates that whether the
frame carries IEEE 802.1Q tag information. SP TPID (Service Provider Tag Protocol
Identifier) is the service provider VLAN stacking tag type. Many vendors use 0x8100 or
0x9100.
TPID (Tag Protocol Identifier) is the customer IEEE 802.1Q tag.
• If the VLAN stacking port role is Access Port , then the Switch adds the SP TPID tag to
all incoming frames on the service provider's edge devices (1 and 2 in the VLAN stacking
example figure).
• If the VLAN stacking port role is Tunnel Port , then the Switch only adds the SP TPID
tag to all incoming frames on the service provider's edge devices (1 and 2 in the VLAN
stacking example figure) that have an
SP TPID different to the one configured on the
Switch. (If an incoming frame’s SP TPID is the same as the one configured on the Switch,
then the Switch will not add the tag.)
Priority refers to the IEEE 802.1p standard that allows the service provider to prioritize traffic
based on the class of service (CoS) the customer has paid for.
• On the Switch, configure priority level of the inner IEEE 802.1Q tag in the Port Setup
screen.
• "0" is the lowest priority level and "7" is the highest.
VID is the VLAN ID. SP VID is the VID for the second (service provider’s) VLAN tag.
21.3.1 Frame Format
The frame format for an untagged Ethernet frame, a single-tagged 802.1Q frame (customer)
and a “double-tagged” 802.1Q frame (service provider) is shown next.
Configure the fields as highlighted in the Switch
VLAN Stacking screen.
Table 50 VLAN Tag Format
Type Priority VID
Table 51 Single and Double Tagged 802.11Q Frame Format
DA SA Len/
Etype
Data FCS Untagged
Ethernet frame
DA SA TPID Priority VID Len/
Etype
Data FCS IEEE 802.1Q
customer
tagged frame
DA SA SPTPID Priority VID TPID Priority VID Len/
Etype
Data FCS Double-tagged
frame
Table 52 802.1Q Frame
DA Destination Address Priority 802.1p Priority
SA Source Address Len/
Etype
Length and type of Ethernet frame