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A-1
APPENDIX A
VIRTUAL LANS (VLANS)
A.1 VLANS AND FRAME TAGGING
The ELS10-27TX supports IEEE 802.1Q-compliant virtual LANs (VLANs). This
capability provides a highly efficient architecture for establishing VLANs within a
network and for controlling broadcast/multicast traffic between workgroups.
Central to this capability is an explicit frame tagging approach for carrying VLAN
information between interconnected network devices.
With frame tagging, a four-byte data tag field is appended to frames that cross the
network. The tag identifies which VLAN the frame belongs to. The tag may be
added to the frame by the end station itself or by a network device, such as a switch.
In the example in Figure A-1 below, the workstations attached to the top switch are
members of the same two VLANs as the workstations attached to the bottom
switch. The 802.1Q tags are used to carry VLAN information in the frames
traveling between the two switches.
* Note is true if it does not have a tag and is a hybrid port, or the port is an
access port.
* Note is only stripped, if the hybrid port and the tag in the packet matches the
PVID or is an access port.
Figure A-1. Two-Switch VLAN Configuration
2X 4X 6X 8X 10X 12X 14X 16X 18X 20X 22X 24X
26
27
RESET
ELS10-27TX
EPIM100
PWR
CPU
ETHERNET SWITCH
25X 26X 27X
10BASE-T/100BASE-TX
COM
LINK
STATUS
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STATUS
LINK
STATUS
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PORT STATUS MODE
STATUS
TXACT FDXMON
RXCOL 100USR
2X 4X 6X 8X 10X 12X 14X 16X 18X 20X 22X 24X
26
27
RESET
ELS10-27TX
EPIM100
PWR
CPU
ETHERNET SWITCH
25X 26X 27X
10BASE-T/100BASE-TX
COM
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
STATUS
LINK
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STATUS
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STATUS
LINK
STATUS
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STATUS
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STATUS
PORT STATUS MODE
STATUS
TXACT FDXMON
RXCOL 100USR
VLAN Y
VLAN Y
802.1Q tag added
by Incoming port*
802.1Q tag carries
VLAN Identifier
802.1Q used by
switch to determine
VLAN, then stripped
by forwarding port*
1
2
3
VLAN X
VLAN X
1
3