Extreme Networks Summit1 manual Uses of Tagged Vlans

VIRTUAL LANS (VLANS)

USES OF TAGGED VLANS

Tagging is most commonly used to create VLANs that span switches. The switch-to-switch connections are typically called trunks. Using tags, multiple VLANs can span multiple switches using one or more trunks. In a port-based VLAN, each VLAN requires its own pair of trunk ports, as shown in Figure 5-3. Using tags, multiple VLANs can span two switches with a single trunk.

Another benefit of tagged VLANs is the ability to have a port be a member of multiple VLANs. This is particularly useful if you have a device (such as a server) that must belong to multiple VLANs. The device must have a NIC that supports 802.1Q tagging.

A single port can be a member of only one port-based VLAN. All additional VLAN membership for the port must be accompanied by tags. In addition to configuring the VLAN tag for the port, the server must have a Network Interface Card (NIC) that supports 802.1Q tagging.

ASSIGNING A VLAN TAG

Each VLAN may be assigned an 802.1Q VLAN tag. As ports are added to a VLAN with an 802.1Q tag defined, you decide whether each port will use tagging for that VLAN. The default mode of the switch is to have all ports assigned to the VLAN named “default,” with an 802.1Q VLAN tag (VLANid) of 1 assigned.

Not all ports in the VLAN must be tagged. As traffic from a port is forwarded out of the switch, the switch determines (in real time) if each destination port should use tagged or untagged packet formats for that VLAN. The switch adds and strips tags, as required, by the port configuration for that VLAN.

Packets arriving tagged with a VLANid that is not configured in the switch will be discarded.

5-6 SUMMIT SWITCH INSTALLATION AND USER GUIDE