ES-315/ES-315-F User’s Guide
57
C
H A P T E R
7
VLAN
This chapter shows you how to configure 802.1Q tagged VLANs.
7.1 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 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.
7.1.1 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
Содержание ES-315
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Страница 7: ...Safety Warnings ES 315 ES 315 F User s Guide 7 ...
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Страница 10: ...Contents Overview ES 315 ES 315 F User s Guide 10 ...
Страница 21: ...21 PART I Introduction and Hardware Getting to Know Your Switch 23 Hardware Overview 27 ...
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Страница 26: ...Chapter 1 Getting to Know Your Switch ES 315 ES 315 F User s Guide 26 ...
Страница 29: ...Chapter 2 Hardware Overview ES 315 ES 315 F User s Guide 29 Figure 7 Base Panel ES 315 F POWER ...
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Страница 84: ...Chapter 13 Multicast ES 315 ES 315 F User s Guide 84 Figure 41 MVR Group Configuration Example ...
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Страница 90: ...Chapter 14 Static Route ES 315 ES 315 F User s Guide 90 ...
Страница 91: ...91 PART V Management Maintenance 93 Access Control 99 Diagnostic 113 Syslog 115 MAC Table 119 ARP Table 121 ...
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Страница 112: ...Chapter 16 Access Control ES 315 ES 315 F User s Guide 112 ...
Страница 114: ...Chapter 17 Diagnostic ES 315 ES 315 F User s Guide 114 ...
Страница 118: ...Chapter 18 Syslog ES 315 ES 315 F User s Guide 118 ...
Страница 123: ...Chapter 20 ARP Table ES 315 ES 315 F User s Guide 123 ...
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Страница 125: ...125 PART VI Troubleshooting and Product Specifications Troubleshooting 127 Product Specifications 131 ...
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Страница 136: ...Chapter 22 Product Specifications ES 315 ES 315 F User s Guide 136 ...
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Страница 152: ...Appendix B Common Services ES 315 ES 315 F User s Guide 152 ...
Страница 156: ...Appendix C Legal Information ES 315 ES 315 F User s Guide 156 ...
Страница 162: ...Appendix D Customer Support ES 315 ES 315 F User s Guide 162 ...