GS-2024 User’s Guide
77
C
H A P T E R
8
VLAN
The type of screen you see here depends on the
VLAN Type
you selected in the
Switch Setup
screen. This chapter shows you how to configure 802.1Q tagged and port-based 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 for the TPID (Tag Protocol Identifier, residing within
the type/length field of the Ethernet frame) and two bytes for the TCI (Tag Control
Information, starting 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 the value 4095 (FFF) is reserved, so the maximum possible
number of VLAN configurations is 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 VLAN-aware switch, the Switch first decides
where to forward the frame, and then inserts a VLAN tag reflecting the ingress port's default
VID. The default PVID is VLAN 1 for all ports, but this can be changed.
A broadcast frame (or a multicast frame for a multicast group that is known by the system) is
duplicated only on ports that are members of the VID (except the ingress port itself), thus
confining the broadcast to a specific domain.
TPID
2 Bytes
User Priority
3 Bits
CFI
1 Bit
VLAN ID
12 bits
Summary of Contents for Dimension GS-2024
Page 2: ......
Page 7: ...Safety Warnings GS 2024 User s Guide 7 This product is recyclable Dispose of it properly ...
Page 8: ...Safety Warnings GS 2024 User s Guide 8 ...
Page 26: ...List of Tables GS 2024 User s Guide 26 ...
Page 28: ...28 ...
Page 36: ...Chapter 2 Hardware Installation and Connection GS 2024 User s Guide 36 ...
Page 44: ...44 ...
Page 62: ...Chapter 6 System Status and Port Statistics GS 2024 User s Guide 62 ...
Page 70: ...Chapter 7 Basic Setting GS 2024 User s Guide 70 Figure 27 Basic Setting IP Setup ...
Page 74: ...Chapter 7 Basic Setting GS 2024 User s Guide 74 ...
Page 76: ...76 ...
Page 88: ...Chapter 8 VLAN GS 2024 User s Guide 88 ...
Page 110: ...Chapter 13 Mirroring GS 2024 User s Guide 110 ...
Page 120: ...Chapter 15 Port Authentication GS 2024 User s Guide 120 ...
Page 138: ...Chapter 18 Multicast GS 2024 User s Guide 138 ...
Page 152: ...Chapter 19 Authentication Accounting GS 2024 User s Guide 152 ...
Page 157: ...157 PART IV IP Application Static Route 159 Differentiated Services 163 DHCP 167 ...
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Page 162: ...Chapter 21 Static Route GS 2024 User s Guide 162 ...
Page 166: ...Chapter 22 Differentiated Services GS 2024 User s Guide 166 ...
Page 174: ...174 ...
Page 198: ...Chapter 25 Access Control GS 2024 User s Guide 198 ...
Page 200: ...Chapter 26 Diagnostic GS 2024 User s Guide 200 ...
Page 204: ...Chapter 27 Syslog GS 2024 User s Guide 204 ...
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Page 222: ...Chapter 32 Troubleshooting GS 2024 User s Guide 222 ...
Page 230: ...Chapter 33 Product Specifications GS 2024 User s Guide 230 ...
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Page 240: ...Appendix A Pop up Windows JavaScripts and Java Permissions GS 2024 User s Guide 240 ...
Page 252: ...Appendix C Legal Information GS 2024 User s Guide 252 ...
Page 258: ...Appendix D Customer Support GS 2024 User s Guide 258 ...
Page 266: ...Index GS 2024 User s Guide 266 ...