Cabletron Systems 802.1Q Manual De Usuario

 

VLAN Operation

 

 depicts the inside of a switch with six ports, numbered one 

through six. The switch has been configured to associate VLAN A and B 
with FID 2, VLAN C and D with FID 3, and VLAN E with FID 4. Port 6 
has been classified as a 1Q Trunk Port. This classification establishes that 
all VLANs are members of the Port VLAN List for Port 6 and the frames 
transmitted for all VLANs will contain a tag header. Also the PVID for 
Port 6 is set to the default VLAN with its corresponding relationship to 
FID 1. Although untagged frames are not usually present on a 1Q Trunk 
Port, any untagged frames received would need to be classified if the port 
has not been configured to drop all untagged frames.

 

When a switch is placed in 802.1Q Operational Mode, every frame 
received by the switch must belong, or be assigned, to a VLAN.

 

The switch receives a frame from Port 1 and examines the frame. The 
switch notices that this frame does not currently have a VLAN tag. The 
switch recognizes that Port 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. 

 

A VLAN ID is always assigned to a port. By default, it is the 
Default VLAN (VLAN ID = 1). 

Port 4

2599-02

Port 3

Port 6

Port 2

Port 1

Port 5