3Com TR manual Connecting Common VLANs Between Switch Units, Using Non-routable Protocols, Example

7-4CHAPTER 7: VIRTUAL LANS

Connecting Common VLANs Between Switch Units

In the Switch 2000 TR, you typically connect VLANs to other Switch 2000 TRs and units using backbone ports. This allows the Switch to forward all frames with an unknown address to the rest of the network, and it also stops the Switch Database from becoming full if there are more than 500 addresses in the net- work. Note that you normally require one backbone port per VLAN.

In addition, to make the Switch-to-Switch connec- tions more cost-effective, the Switch 2000 TR allows you to specify that one port forms part of a Virtual LAN Trunk (VLT). A VLT is a connection that carries traffic for multiple VLANs between Switch units. If you configure both ends of a Switch-to-Switch con- nection as part of a VLT, you only need that one con- nection for all the VLANs.

NOTE: VLTs can only be used for links between SuperStack II Switch 2000 TR units. You cannot use VLTs for Switch-router links.

If you specify that a backbone port on one VLAN is part of a VLT, that backbone port becomes a back- bone port for all the VLANs on the Switch, even if they had no backbone port before. If you subse- quently disable the VLT function on that port, the port becomes the backbone port for the Default VLAN (VLAN 1) and all other VLANs lose their backbone ports.

Using Non-routable Protocols

If you are running non-routable protocols on your network (for example, DEC LAT or NETBIOS), devices

within one VLAN will not be able to communicate with devices in a different VLAN.

Using Unique MAC Addresses

If you connect a server with multiple network adapt- ers to the Switch, we recommend that you configure each network adapter with a unique MAC address.

Extending VLANs into an ATM Network

If the Switch has an ATM OC-3c Module installed, you can extend the VLANs you have defined in your exist- ing network into an ATM network. For more informa- tion, see the SuperStack II Switch ATM OC-3c Module User Guide.

Example 1

The example shown in Figure 7-2 illustrates a simple VLAN configuration with a single Switch 2000 TR whose ports are divided between two VLANs. VLAN 1 is able to talk to VLAN 2 using the connection between each VLAN and the router.

To set up this configuration:

1Use the VT100 screens or VLAN Server database to: a Place ports 1-6 in VLAN 1.

b Place ports 7-12 in VLAN 2.

2Connect a port in VLAN 1 to the router.

3Repeat steps 2 and 3 for VLAN 2.