3Com 4.2.2 manual Non-ATM VLANs, Tag-based VLANs

An Introduction to ATM and VLAN Management Basics C-11

the configuration is such, the network manager should ensure that IP connectivity to the device is not affected by VLAN moves.

The Default VLAN When an ATM edge device is initialized, a single VLAN called the default VLAN is created automatically and all ports of the device are assigned to it.

In the SuperStack II Switch 2700 module, the Admin VLAN is also used as the Default VLAN when the SuperStack II Switch 2700 is first initialized. All ports are initially assigned to the Admin VLAN to ensure that they have connectivity to the network. The Network Administrator can then move the ports to another VLAN. At least one port must remain in the Admin VLAN if the device is to be reached for management purposes.

Non-ATM VLANs

VLANs can be created on non-ATM based switches by using either packet-taggingor packet-filtering(policy-based) techniques. The Superstack II Switch 1000/3000 uses the packet-tagging mechanism. VLAN management in the Superstack II Switch 1000/3000 system is supported by a “VLAN Server” - a database which stores and retrieves information about station VLAN membership.

The CoreBuilder 2500/6000 uses packet-filtering. The CoreBuilder 2500/6000 can link up with Emulated LANs to create policy-based Virtual LANs “over ATM.” The following sections describe both these VLAN mechanisms.

Tag-based VLANs

In tag-basedVLANS, as employed by the Superstack II Switch 1000/3000, ports can be grouped across multiple switches to form a single broadcast domain. Packets within each VLAN group are tagged with a unique identifier. The switches segment the traffic using these identifiers. Each Superstack II Switch 1000 can support up to 16 VLANs and you can have more than 16 VLANs in your entire network by connecting the 16 Switch VLANs to other VLANS using a router.

Virtual LAN Trunk VLANs can be defined in a single switch unit or can span several Switch units. When a VLAN spans two switch units, they are connected using backbone ports. The tagging method, described below, makes it possible for a single backbone port to carry the traffic for all VLANs defined in a switch. In that case, the backbone port is referred to as a Virtual LAN