Forwarding Tagged/Untagged Frames
Virtual LANs (VLANs)
B-3
2.3
FORWARDING TAGGED/UNTAGGED FRAMES
Ports can be assigned to multiple tagged or untagged VLANs. Each port on the switch is therefore
capable of passing tagged or untagged frames. To forward a frame from a VLAN-aware device to a
VLAN-unaware device, the switch first decides where to forward the frame, and then strips off the
VLAN tag. However, to forward a frame from a VLAN-unaware device to a VLAN-aware device,
the switch first decides where to forward the frame, and then inserts a VLAN tag reflecting this
port’s default VID. The default PVID is VLAN 1, but this can be changed as described in
Section 7.15
.
Figure B-1
Example of Multi-Switch VLAN Configuration
B.4
FORWARDING TRAFFIC WITH UNKNOWN VLAN TAGS
Up to 4096 VLANs are supported by the IEEE 802.1Q standard, but this switch only supports
1024 VLANs. Therefore, if this switch is attached to any device that forwards frames with
unknown VLAN tags, or to end stations which issue VLAN registration requests for unknown
VLANs, this traffic will be dropped.
VLAN 1.2
(802.1Q tags)
VLAN 1
(802.1Q tags)
Trunk
VLAN 1.2
(802.1Q tags)
VLAN 3
(untagged)
3583_02
VLAN 1.2
(802.1Q tags)
VLAN 3
(untagged)
VLAN-aware switch
VLAN-aware switch
VLAN-aware switch
VLAN-aware switch
VLAN-aware switch
VLAN-aware switch
