Cabletron Systems 802.1Q Manual De Usuario

Chapter 4: Examples

The following describes how, when User A attempts to log on to the File 
Server on Bridge 4, the frames from User A are classified on Switch 4 and 
traverse the network. In this example, the MAC address of User A is “Y” 
and the MAC address for the File Server is “Z”. The following description 
includes illustrations to help understand how the frames flow through the 
network.

User A sends a frame with a Broadcast Destination Address in an 
attempt to locate the File Server. The frame is received on User A’s 
port of Bridge 1 and, because the frame is a broadcast frame, it is 
transmitted out all ports of Bridge 1 as shown in 

.

Switch 4 receives the frame from Bridge 1 and immediately classifies 
it as belonging to the Red VLAN. After the frame is classified, 
Switch 4 checks the Destination Address and, upon discovering that it 
is a Broadcast Destination Address, forwards the frame out all ports in 
the Red VLAN Forwarding List excluding Port 1, which received the 
frame. In this example, it is only Port 4.

Switch 4 updates its Source Address Table in FID 2 if it didn’t already 
have a dynamic entry for MAC address “Y” in FID 2. Because 
Switch 4 received the frame on Port 1, it does not forward the frame 
out that port, but does forward the frame to Port 4. 

The frame is transmitted to Switch 2 with a VLAN Tag Header 
inserted in the frame. The VLAN Tag Header indicates that the frame 
is classified as belonging to the Red VLAN. 

taken to this point to reach Switch 2.

Floor 4

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1

3

2

Bridge 1

Bridge 2

4

4