Enterasys Networks 6H3xx Betriebsanweisung

IEEE 802.1Q VLAN switches act on the classification of frames into VLANs. Sometimes, VLAN 
classification is based on tags in the headers of data frames. These VLAN tags are added to data 
frames by the switch as the frames are transmitted out certain ports, and are later used to make 
forwarding decisions by the switch and other VLAN-aware switches. In the absence of a VLAN 
tag header, the classification of a frame into a particular VLAN depends upon the configuration of 
the switch port that received the frame.

The operation of an 802.1Q VLAN switch is best understood from a point of view of the switch 
itself. To illustrate this concept, the examples that follow view the switch operations from inside 
the switch. 

 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 Filtering Database Identifier (FDB ID) 2, 
VLAN C and D with FDB ID 3, and VLAN E with FDB ID 4. Port 6 has been classified to serve 
as a VLAN trunk connection (will only transmit and receive tagged frames). 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 FDB ID 1. Although untagged frames are not usually 
present on a VLAN trunk connection, any untagged frames received would need to be classified if 
the port has not been configured to drop all untagged frames.

NOTE: The example in 

 shows ports sharing the same FDB ID, which is 

supported by the switch. However, this feature cannot be configured using Local 
Management at this time, but it can be configured using an SNMP management 
application.

Port 4

2599-02

Port 3

Port 6

Port 2

Port 1

Port 5