3Com NJ220 - IntelliJack Switch Caratteristiche Manuale - Pagina 2
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3 C O M
®
N J 2 0 5 I N T E L L I J A C K
What is a Virtual LAN
(VLAN)?
C O N T E N T S
What is a Virtual LAN (VLAN)?................2
Benefits...............................................2
How VLANS Work ...............................2
VLAN Configuration and Setup ..............3
Setting the PAN Port Associations........5
Incoming Tag Schemes ........................6
What is Traffic Prioritization? ..................8
Benefits...............................................8
How Traffic Prioritization Works ..........8
Configuration and Setup ........................9
Setting Priority Tag Values ...................9
Schedule Policy..................................11
Business Application .............................12
For More Information ...........................12
Appendix A: Default Settings................13
Appendix B: Additional Notes...............14
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S W I T C H - V L A N S & T R A F F I C P R I O R I T I Z AT I O N
A VLAN is a logical subnet grouping that can be assigned to users, logins, or systems-
independently of the physical network infrastructure. An IEEE 802.1Q-compliant
VLAN is equivalent to a Layer 2 broadcast domain.
Systems or users associated with a particular VLAN subnet can communicate freely.
Network logins and end systems can be centrally managed as though they were physi-
cally located in the same site, regardless of the actual topology of the network.
Benefits
Support for port-based VLANs enables the 3Com
IT and business benefits. For example, it can help:
• Reduce the costs of IT equipment moves, upgrades, and other changes
• Centralize and automate network administration
• Create and monitor virtual workgroups for a specific department or section, with most
of the traffic staying in the same VLAN broadcast domain
• Isolate broadcast, multicast, and unicast traffic to a single subnet domain
• Reduce traffic congestion and prevent network flooding
• Accelerate network performance without expensive router hardware
• Control communication among broadcast domains
How VLANS Work
In order to properly forward VLAN traffic, core network switches and management
platforms check each Ethernet frame for an IEEE 802.1Q VLAN tag. Each tag is identi-
fied by a unique VLAN ID (VID), which can be a number between 1 and 4095.
IEEE 802.1Q-compliant NJ205 IntelliJack Switches support the following VLAN functionality:
Forwarding Inbound-Traffic from the LAN
The NJ205 IntelliJack Switch forwards voice, data, and video packets based on their
MAC addresses, not Ethernet frame tags. However, this 802.1Q-compliant Ethernet-data
switch can be configured to:
• Check incoming traffic for VLAN tags
• Modify outbound traffic to include VLAN tags
• Forward VLAN-tagged traffic
This supports other devices that rely on Ethernet frame tags to correctly recognize and
forward VLAN traffic. The section titled, Setting the Ingress and Egress Modes, provides
step-by-step details on how to configure these capabilities.
Forwarding Traffic Among PAN Ports
Port Associations regulate traffic between the PAN (device) ports on the same switch.
Port Associations only distribute traffic at the four PAN ports and have no effect on
traffic entering or leaving the switch, or going out to the LAN.
Port Associations can be configured in any combination among PAN ports belonging to
the same switch. For example, Port #1 can be associated to any other port, all three, or
none of them. For details on how to set up Port Associations, refer to the section titled,
Setting PAN Port Associations.
Table 1. Summary of 802.1Q VLAN Functionality
Feature
Function
Ingress/egress rules
Applied at the LAN port (uplink port) only
VLAN tags
One VLAN tag can be set per PAN port
Traffic prioritization
802.1p traffic prioritization supported through four, port-based hardware queues
Inbound unicast traffic
Ethernet frames forwarded based on the MAC addresses; no exceptions
Inbound multicast traffic
All Ethernet frames forwarded to all ports regardless of tags
Inbound broadcast traffic
All Ethernet frames forwarded to all ports regardless of tags
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NJ205 IntelliJack
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to deliver significant