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Chapter 5
| VLAN Configuration
IEEE 802.1Q VLANs
Assigning Ports to VLANs
Before enabling VLANs for the switch, you must first assign each port to the VLAN
group(s) in which it will participate. By default all ports are assigned to VLAN 1 as
untagged ports. Add a port as a tagged port if you want it to carry traffic for one or
more VLANs, and any intermediate network devices or the host at the other end of
the connection supports VLANs. Then manually assign ports on the other VLAN-
aware network devices along the path that will carry this traffic to the same
VLAN(s). However, if you want a port on this switch to participate in one or more
VLANs, but none of the intermediate network devices nor the host at the other end
of the connection supports VLANs, then you should add this port to the VLAN as an
untagged port.
Note:
VLAN-tagged frames can pass through VLAN-aware or VLAN-unaware
network interconnection devices, but the VLAN tags should be stripped off before
passing it on to any end-node host that does not support VLAN tagging.
Figure 63: VLAN Compliant and VLAN Non-compliant Devices
VA
tagged
frames
VA
VLAN Classification – When the switch receives a frame, it classifies the frame in
one of two ways. If the frame is untagged, the switch assigns the frame to an
associated VLAN (based on the default VLAN ID of the receiving port). But if the
frame is tagged, the switch uses the tagged VLAN ID to identify the port broadcast
domain of the frame.
Port Overlapping – Port overlapping can be used to allow access to commonly
shared network resources among different VLAN groups, such as file servers or
printers. Note that if you implement VLANs which do not overlap, but still need to
communicate, you can connect them by enabled routing on this switch.
Untagged VLANs – Untagged VLANs are typically used to reduce broadcast traffic
and to increase security. A group of network users assigned to a VLAN form a
broadcast domain that is separate from other VLANs configured on the switch.
Packets are forwarded only between ports that are designated for the same VLAN.
Untagged VLANs can be used to manually isolate user groups or subnets. However,
you should use IEEE 802.3 tagged VLANs whenever possible to automate VLAN
registration.
tagged frames
untagged
frames
VA
– 124 –
VA
VA: VLAN Aware
VU: VLAN Unaware
VU
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