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IES-1000 User’s Guide
IEEE 802.1Q Tagged VLAN Commands 9-5
Next the switch checks the VLAN ID (VID) of tagged frames or assigns temporary VIDs to untagged frames (see
the PVID Command).
The switch then checks the VID in a frame’s tag against the SVLAN table.
The switch notes what the SVLAN table says (that is, the SVLAN tells the switch whether or not to forward a
frame and if the forwarded frames should have tags).
Then the switch applies the port filter to finish the forwarding decision. This means that frames may be dropped
even if the SVLAN says to forward them. Frames might also be dropped if they are sent to a CPE (customer
premises equipment) DSL device that does not accept tagged frames.
The following figure shows the flow of the decision process used with a broadcast frame (one that is meant to go to
all of the ports).
Figure 9-4 SVLAN Example
An untagged frame comes in from the LAN.
The switch checks the PVID table and assigns a temporary VID of 1.
The switch ignores port# 1 (the LAN port where the frame came in), because the switch does not send a frame to
the port that it came in through.
The switch sees that port #s 2, 3, 4, 6, 8 and 9 (DSL ports 1, 2, 3, 5, 7 and 9) are all set to “fixed” and “untag”
which means the SVLAN allows the frame to be sent to those ports without a tag.
Port # 5 is “forbidden” so the frame is not forwarded to DSL port # 4.