User`s guide

Chapter 3:

VLAN Operation

3-4 Port Based VLAN User’s Guide

Figure 3-1 Inside the Switch

3.4.1 Receiving Frames from VLAN Ports

When a switch is placed in 802.1Q Operational Mode, every frame

received by the switch must belong to a VLAN.

Untagged Frames

The switch receives a frame from Interface 1 and examines the frame. The

switch notices that this frame does not currently have a VLAN tag. The

switch recognizes that Interface 1 is a member of VLAN A, and classiﬁes

the frame as such. In this fashion, all untagged frames entering a VLAN

switch assume membership in a VLAN.

The switch will now make a forwarding decision on the frame based on

its mode of operation, as described in Section 3.4.2, Forwarding

Decisions.

NOTE

If a VLAN ID has not been assigned to a port by the

Administrator, the switch will classify frames received from that

port as belonging to the Default VLAN (VLAN ID = 1)

Interface 1

Interface 2

Interface 4

Interface 3

all

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