GS-1524/GS-1548 User’s Guide
57
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H A P T E R
8
VLAN
This chapter shows you how to configure IEEE 802.1Q tagged VLANs.
8.1 Introduction to IEEE 802.1Q Tagged VLANs
A tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the
VLAN membership of a frame across bridges - they are not confined to the switch
on which they were created. The VLANs can be created statically by hand or
dynamically through GVRP. The VLAN ID associates a frame with a specific VLAN
and provides the information that switches need to process the frame across the
network. A tagged frame is four bytes longer than an untagged frame and
contains two bytes of TPID (Tag Protocol Identifier, residing within the type/length
field of the Ethernet frame) and two bytes of TCI (Tag Control Information, starts
after the source address field of the Ethernet frame).
The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for
Ethernet switches. If a frame received at an Ethernet port has a CFI set to 1, then
that frame should not be forwarded as it is to an untagged port. The remaining
twelve bits define the VLAN ID, giving a possible maximum number of 4,096
VLANs. Note that user priority and VLAN ID are independent of each other. A
frame with VID (VLAN Identifier) of null (0) is called a priority frame, meaning that
only the priority level is significant and the default VID of the ingress port is given
as the VID of the frame. Of the 4096 possible VIDs, a VID of 0 is used to identify
priority frames and value 4095 (FFF) is reserved, so the maximum possible VLAN
configurations are 4,094.
8.1.1 Forwarding Tagged and Untagged Frames
Each port on the Switch is capable of passing tagged or untagged frames. To
forward a frame from an 802.1Q VLAN-aware switch to an 802.1Q VLAN-unaware
switch, the Switch first decides where to forward the frame and then strips off the
VLAN tag. To forward a frame from an 802.1Q VLAN-unaware switch to an 802.1Q
TPID
2 Bytes
User Priority
3 Bits
CFI
1 Bit
VLAN ID
12 bits
Содержание GS-1524
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Страница 8: ...Safety Warnings GS 1524 GS 1548 User s Guide 8 ...
Страница 10: ...Contents Overview GS 1524 GS 1548 User s Guide 10 ...
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Страница 26: ...Chapter 2 Hardware Installation and Connection GS 1524 GS 1548 User s Guide 26 ...
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Страница 42: ...Chapter 4 The Web Configurator GS 1524 GS 1548 User s Guide 42 ...
Страница 52: ...Chapter 6 Port Settings GS 1524 GS 1548 User s Guide 52 ...
Страница 62: ...Chapter 8 VLAN GS 1524 GS 1548 User s Guide 62 ...
Страница 82: ...Chapter 12 Port Rate Limit and Storm Control GS 1524 GS 1548 User s Guide 82 ...
Страница 86: ...Chapter 13 Layer 2 L2 Management GS 1524 GS 1548 User s Guide 86 ...
Страница 92: ...Chapter 15 Auto Denial of Service DoS GS 1524 GS 1548 User s Guide 92 ...
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Страница 136: ...Chapter 19 RMON Lite GS 1524 GS 1548 User s Guide 136 ...
Страница 144: ...Chapter 21 Troubleshooting GS 1524 GS 1548 User s Guide 144 ...
Страница 150: ...Chapter 22 Product Specifications GS 1524 GS 1548 User s Guide 150 ...
Страница 151: ...151 PART IV Appendices and Index IP Addresses and Subnetting 151 Legal Information 163 Index 167 ...
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Страница 166: ...Appendix B Legal Information GS 1524 GS 1548 User s Guide 166 ...