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Example 2, VLANs Across Multiple Switches
802.1Q VLAN User’s Guide 4-9
The VLAN Tag Header is inserted because Switch 4, Port 4 is
designated as an 802.1Q Trunk port. In this case, the Port Mode setting
for Port 4 is 802.1Q Trunk and the VLAN Frame format for that
VLAN is tagged.
Figure 4-5 Transmitting to Switch 4
3. When Switch 2 receives the tagged frame on its Port 2, it checks the
frame’s VLAN Tag Header and determines that the frame is classified
as belonging to the Red VLAN, and that the frame is a broadcast
frame. Switch 2 forwards the frame to all ports in the Red VLAN
Forwarding List excluding Port 2, which received the frame. In this
example, the only eligible port is Port 3, which connects to Bridge 4.
Switch 2 checks its Forwarding List, which specifies that the VLAN
frame type for that port is untagged. Switch 2 then updates its Source
Address Table in FID 3 for MAC address “Y” if necessary. The
untagged frame is then transmitted out Port 3 to Bridge 4. Bridge 4
forwards the frame out all its ports because it is a broadcast frame, and
the server receives it as shown in Figure 4-6.
Floor 2
22631_15
Floor 3
Floor 4
Bridge 1 Bridge 2
Bridge 3
Bridge 4
Redco
Redco
Blue Industries
Blue Industries
Red VLAN
Red VLAN
Red VLAN
Red VLAN
Blue VLAN
Blue VLAN
Blue VLAN
Blue VLAN
User A
File Server
4
2
1
2
3
4
1
2
3