3Com 3824 Implementation Guide - Page 66

Creating New VLANs, VLANs: Tagged and Untagged Membership

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66 CHAPTER 8: SETTING UP VIRTUAL LANS Figure 17 Two VLANs connected via a router Creating New VLANs If you want to move a port from the Default VLAN to another VLAN, you must first define information about the new VLAN on your Switch. VLANs: Tagged and Untagged Membership Your Switch supports 802.1Q VLAN tagging, a system that allows traffic for multiple VLANs to be carried on a single physical (backbone) link. When setting up VLANs you need to understand when to use untagged and tagged membership of VLANs. Quite simply, if a port is in a single VLAN it can be an untagged member, but if the port needs to be a member of multiple VLANs, tagged membership must be defined. Typically endstations (for example, clients) will be untagged members of one VLAN, while inter-Switch connections will be tagged members of all VLANs. The IEEE Std 802.1Q-1998 defines how VLANs operate within an open packet-switched network. An 802.1Q compliant packet carries additional information that allows a Switch to determine to which VLAN the port belongs. If a frame is carrying the additional information, it is known as tagged. To carry multiple VLANs across a single physical (backbone) link, each packet must be tagged with a VLAN identifier so that the Switches can

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66
C
HAPTER
8: S
ETTING
U
P
V
IRTUAL
LAN
S
Figure 17
Two VLANs connected via a router
Creating New VLANs
If you want to move a port from the Default VLAN to another VLAN, you
must first define information about the new VLAN on your Switch.
VLANs: Tagged and
Untagged
Membership
Your Switch supports 802.1Q VLAN tagging, a system that allows traffic
for multiple VLANs to be carried on a single physical (backbone) link.
When setting up VLANs you need to understand when to use untagged
and tagged membership of VLANs. Quite simply, if a port is in a single
VLAN it can be an untagged member, but if the port needs to be a
member of multiple VLANs, tagged membership must be defined.
Typically endstations (for example, clients) will be untagged members of
one VLAN, while inter-Switch connections will be tagged members of all
VLANs.
The IEEE Std 802.1Q-1998 defines how VLANs operate within an open
packet-switched network. An 802.1Q compliant packet carries additional
information that allows a Switch to determine to which VLAN the port
belongs. If a frame is carrying the additional information, it is known as
tagged
.
To carry multiple VLANs across a single physical (backbone) link, each
packet must be tagged with a VLAN identifier so that the Switches can