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Forwarding Tagged/Untagged Frames
If you want to create a small port-based VLAN for devices attached
directly to a single switch, you can assign ports to the same untagged
VLAN. However, to participate in a VLAN group that crosses several
switches, you should create a VLAN for that group and enable tagging on
all ports.
Ports can be assigned to multiple tagged or untagged VLANs. Each port
on the switch is therefore capable of passing tagged or untagged frames.
When forwarding a frame from this switch along a path that contains any
VLAN-aware devices, the switch should include VLAN tags. When
forwarding a frame from this switch along a path that does not contain any
VLAN-aware devices (including the destination host), the switch must first
strip off the VLAN tag before forwarding the frame. When the switch
receives a tagged frame, it will pass this frame onto the VLAN(s) indicated
by the frame tag. However, when this switch receives an untagged frame
from a VLAN-unaware device, it first decides where to forward the frame,
and then inserts a VLAN tag reflecting the ingress port’s default VID.
Port-based VLAN
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