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Chapter 4: Examples
4-14 802.1Q VLAN User’s Guide
2. Switch 4 receives the frame and classifies this new untagged frame as
belonging to the Red VLAN. Since the frame is a broadcast, it is
forwarded to any ports that are classified as eligible to receive Red
VLAN frames. Switch 4 also updates its Source Address Table for
FID 1, identifying User B as being located out Port 1.
On Switch 4, the only port eligible to receive Red VLAN frames is
Port 4, the 1Q Trunk. The frame is forwarded out Port 4 with the Red
VLAN Tag header being added, as shown in Figure 4-8.
Figure 4-8 Bridge 1 Broadcasts Frames
3. Switch 2 receives the tagged Red VLAN frame on Port 2, as shown in
Figure 4-9. The VLAN Tag in the frame is maintained, classifying the
frame as belonging to the Red VLAN. The switch forwards the
broadcast frame out all the eligible ports, Ports 3 and 4. Switch 2
simultaneously updates its Source Address Table for FID 1 to reflect
the location of User B (Port 2).
The frame forwarded out Port 3 has its VLAN Tag stripped before
transmission, and it is passed to Bridge 4 as a normal broadcast frame.
The frame that is transmitted out Port 4, the 1Q Trunk, retains its
VLAN tag.
Floor 4
1
Bridge 1 Bridge 2
Red VLAN
Red VLAN
Blue VLAN
Blue VLAN
User B
2
4
3
4
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