User guide

90 ExtremeWare 7.2e Installation and User Guide

Virtual LANs (VLANs)

Figure 13: Two port-based VLANs spanning two switches

VLAN Accounting spans system 1 and system 2 by way of a connection between system 2, port 1X and

system 1, slot 1, port 6. VLAN Engineering spans system 1 and system 2 by way of a connection between

system 2, port 2X, and system 1, slot 8, port 6.

Using this configuration, you can create multiple VLANs that span multiple switches, in a

daisy-chained fashion. Each switch must have a dedicated port for each VLAN. Each dedicated port

must be connected to a port that is a member of its VLAN on the next switch.

Tagged VLANs

Tagging is a process that inserts a marker (called a tag) into the Ethernet frame. The tag contains the

identification number of a specific VLAN, called the VLANid.

NOTE

The use of 802.1Q tagged packets may lead to the appearance of packets slightly bigger than the

current IEEE 802.3/Ethernet maximum of 1,518 bytes. This may affect packet error counters in other

devices, and may also lead to connectivity problems if non-802.1Q bridges or routers are placed in the

path.

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 13.

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.

ES4K007A

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System 1

System 2

Accounting

Engineering