3Com 3c17300 Implementation Guide - Page 65

VLANs and Your Switch, The Default VLAN, VLANs help to control traffic

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VLANs and Your Switch 67 ■ VLANs help to control traffic With traditional networks, congestion can be caused by broadcast traffic that is directed to all network devices whether they require it or not. VLANs increase the efficiency of your network because each VLAN can be set up to contain only those devices that need to communicate with each other. VLANs and Your Switch Your Switch provides support for VLANs using the IEEE 802.1Q standard. This standard allows traffic from multiple VLANs to be carried across one physical link. The Switch 4200 Series implements Open VLANS. This means that if an IEEE 802.1Q tagged packet (that is, the packet that contains a VLAN ID) is received at a port and that port is NOT a member of that VLAN, the Switch does not perform any VLAN filtering. As a result a tagged packet will be forwarded if the address has been previously learned by the Switch. However, if the address is unknown, the packet will only be flooded to ports within the VLAN (s) on which the receive port is a member. The IEEE 802.1Q standard allows each port on your Switch to be placed in: ■ Any one VLAN defined on the Switch. ■ Several VLANs at the same time using 802.1Q tagging. The standard requires that you define the following information about each VLAN on your Switch before the Switch can use it to forward traffic: ■ VLAN Name - This is a descriptive name for the VLAN (for example, Marketing or Management). ■ 802.1Q VLAN ID - This is used to identify the VLAN if you use 802.1Q tagging across your network. The Default VLAN A new or initialized Switch contains a single VLAN, the Default VLAN. This VLAN has the following definition: ■ VLAN Name - Default VLAN ■ 802.1Q VLAN ID - 1 (if tagging is required)

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VLANs and Your Switch
67
■
VLANs help to control traffic
With traditional networks, congestion can be caused by broadcast
traffic that is directed to all network devices whether they require it or
not. VLANs increase the efficiency of your network because each
VLAN can be set up to contain only those devices that need to
communicate with each other.
VLANs and Your
Switch
Your Switch provides support for VLANs using the IEEE 802.1Q standard.
This standard allows traffic from multiple VLANs to be carried across one
physical link.
The Switch 4200 Series implements Open VLANS. This means that if an
IEEE 802.1Q tagged packet (that is, the packet that contains a VLAN ID) is
received at a port and that port is NOT a member of that VLAN, the
Switch does not perform any VLAN filtering. As a result a tagged packet
will be forwarded if the address has been previously learned by the
Switch. However, if the address is unknown, the packet will only be
flooded to ports within the VLAN (s) on which the receive port is a
member.
The IEEE 802.1Q standard allows each port on your Switch to be placed
in:
■
Any one VLAN defined on the Switch.
■
Several VLANs at the same time using 802.1Q tagging.
The standard requires that you define the following information about
each VLAN on your Switch before the Switch can use it to forward traffic:
■
VLAN Name
— This is a descriptive name for the VLAN (for example,
Marketing or Management).
■
802.1Q VLAN ID
— This is used to identify the VLAN if you use
802.1Q tagging across your network.
The Default VLAN
A new or initialized Switch contains a single VLAN, the Default VLAN.
This VLAN has the following definition:
■
VLAN Name
— Default VLAN
■
802.1Q VLAN ID
— 1 (if tagging is required)