Asante IntraCore 6524, User Manual

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Advanced Management
Page 4-20
A VLAN localizes flooded traffic to parts of LAN segments rather than to a
whole LAN. VLANs offer a simple and efficient solution that enhances network
performance, bandwidth utilization, and network security by localizing flooded
traffic.
Port-based VLANs are the simplest of many VLAN approaches that solve the
problem of unnecessary flooding. A port-based VLAN allows the administrator
to assign individual ports on a switch to a VLAN. Any broadcast, multicast, or
unknown unicast traffic received on a port in a VLAN is flooded only to the
other ports in the VLAN rather than to all ports in the system. Port-based
VLANs greatly reduce unnecessary traffic in a network.
For the most complete information about configuring VLANs in an 802.1Q
environment, see the standard, available from IEEE <http://www.ieee.org>.
Tagged and Untagged Frames
In a network with only one switch, the switch itself can keep track of which
ports belong to which VLANs.
In a network with multiple switches, information about which VLAN an
Ethernet frame belongs to must be attached to the frame. The VLAN
information is attached by inserting a tag field in the frame, as defined in IEEE
802.1Q. The tag includes the VID to identify the frame’s VLAN. When a port
receives a tagged frame, it can then pass the frame to other port members of the
same VLAN.
When you add a port to a VLAN, you can specify whether or not frames
originating from that port will be tagged. If the port is configured to send
tagged frames, then its traffic will be associated with the VLAN identified in the
tags.
If it receives an untagged frame, a port has no way to determine the originating
VLAN. In that case, the port can be configured to send the frame as is, to
arbitrarily assign a specific tag to the frame, or to drop the frame.
Abbreviations
The following abbreviations are used throughout this section.
FID Filtering ID
GARP Generic Attribute Registration Protocol
GVRP GARP VLAN Registration Protocol
ISL Inter-Switch Link
MGMT Management