3Com 9000 manual Before assigning a VID, review the information in Table

46CHAPTER 4: ADVANCED MANAGEMENT TASKS

■For backplane ports and switch fabric module ports, you must use tagging when these ports are shared by multiple VLANs. (Only one VLAN’s backplane ports can be untagged; in all other VLANs defined across the backplane, the backplane ports must be tagged.) If you tag the backplane port of a switching module for a VLAN, you must also tag the corresponding switch fabric module port in that VLAN.

Devices (end stations, routers, switches, and so forth) that are connected to an explicitly tagged front-panel port must be capable of supporting 802.1Q tagging. If the front-panel port is untagged in the VLAN to which they belong, however, they do not have to support 802.1Q tagging.

VLAN IDs Each VLAN is identified by its VLAN ID (VID). For the VLANs you create, each module keeps track of its used VLAN ID numbers to help you select the next available VLAN ID. Data frames sent by the module are tagged per IEEE 802.1Q (which contains the VID) if tagging is enabled on the transmit port for that VLAN. Tagged IEEE 802.1Q data frames that are received on the module are assigned to the VLAN that corresponds to the VID contained in the tag. The default VLAN uses a VID of 1.

Before assigning a VID, review the information in Table 6.

Table 6 Assigning ID Numbers to VLANs

VLAN ID
Number	Description
VID 0	The null VID. You cannot define or configure VLANs with
	an ID of 0 on a module.
VID 1	Default VLAN assigned by IEEE and 3Com Corporation
VID 4095	Reserved
VID 2–4094	Numbers that you assign when you create VLANs

Terminology Review the following terms:

■Default VLAN — The port-based VLAN interface that is predefined on all Switch Fabric ports and the ports of each switching module without any tagging.

■Protocol suite — On Layer 3 modules, refers to the protocol family associated with a protocol-based or network-based VLAN. The protocol suite is unspecified for the default VLAN and all port-based VLANs.