DELL PC7024 User Manual

VLAN Commands

two TPID values can be different or the same. VLAN normalization, source 

MAC learning, and forwarding are based on the S-TAG value in a received 

frame.
PowerConnect supports configuring one outer VLAN TPID value per switch. 

The global default TPID is 0x88A8, which indicates a Virtual Metropolitan 

Area Network (VMAN).

Independent VLAN Learning (IVL) allows unicast address-to-port mappings 

to be created based on a MAC Address in conjunction with a VLAN ID.
This arrangement associates the MAC Address only with the VLAN on which 

the frame was received. Therefore, frames are forwarded based on their 

unicast destination address as well as their VLAN membership. This 

configuration affords multiple occurrences of an address in the forwarding 

database. Each address associates with a unique VLAN. Care must be taken 

in the administration of networks, as multiple instances of a MAC address, 

each on a different VLAN, can quickly eat up address entries.
Each VLAN is associated with its own forwarding database. Hence the 

number of forwarding databases equals the number of VLANs supported.
The MAC address stored is supplemented by a 2-byte VLAN ID. The first 2 

bytes of a forwarding database entry contain the VLAN ID associated, and the 

next 6 bytes contain the MAC address. There is a one-to-one relationship 

between VLAN ID and FID (forwarding database ID).

The main purpose of Protocol-based VLANs (PBVLANs) is to selectively 

process packets based on their upper-layer protocol by setting up protocol-

based filters. Packets are bridged through user-specified ports based on their 

protocol. 
In PBVLANs, the VLAN classification of a packet is based on its protocol (IP, 

IPX, NetBIOS, and so on). PBVLANs help optimize network traffic because 

protocol-specific broadcast messages are sent only to end stations using that 

protocol. End stations do not receive unnecessary traffic, and bandwidth is 

used more efficiently. It is a flexible method that provides a logical grouping 

of users. An IP subnet or an IPX network, for example, can each be assigned 

2CSPC4.XCT-SWUM2XX1.book  Page 770  Monday, October 3, 2011  11:05 AM