Extreme Networks ExtremeWare XOS 11.1, Руководство пользователя

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Types of VLANs
ExtremeWare XOS 11.1 Concepts Guide
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VLAN Accounting spans system 1 and system 2 by way of a connection between system 2, port 29 and
system 1, slot 1, port 6. VLAN Engineering spans system 1 and system 2 by way of a connection between
system 2, port 32, and system 1, slot 8, port 6.
Using this configuration, you can create multiple port-based 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 4 .
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
Network Interface Card (NIC) that supports IEEE 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.
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.
NOTE
Packets arriving tagged with a VLANid that is not configured on a port will be discarded.
Figure 5 illustrates the physical view of a network that uses tagged and untagged traffic.