Extreme Networks ExtremeWare 7.2e, Installation And User Manual

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94 ExtremeWare 7.2e Installation and User Guide
Virtual LANs (VLANs)
Figure 15: 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 15.
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.
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