Albedo xGenius - C-VLAN and S-VLAN Selection

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User Guide
128
6.2.2. C-VLAN and S-VLAN Selection
Within enterprise networks, VLANs are important because they enable network
segmentation on an organisational basis, by functions, project teams or applications,
rather than on a physical or a geographical basis. The network can be reconfigured
through software, instead of physically unplugging and moving devices or wires.
VLANs are an important contribution to scalable Ethernet networks, because they limit
broadcast traffic inherent to the bridging mechanism. Large amounts of broadcast
traffic may damage performance and even collapse network equipment, which is why
it must be controlled.
Standard IEEE 802.1Q specifies the most popular VLAN frame format. VLAN frames
carry a 16-bit header which specifies the VLAN Identifier (VID) and the frame priority
within the VLAN. Many carrier Ethernet networks use the VID for segmentation just like
enterprises. The VID in carrier Ethernet networks is used by service providers as
general purpose identifier. They can be associated to an specific service, customer,
node or several of them at the same time. Sometimes, service providers use a two-level
VLAN structure. Levels are designated as customer VLAN (C-VLAN) and service
VLAN (S-VLAN). This two-structure is know as Q-in-Q. The standardised version of the
Q-in-Q frame is defined in IEEE 802.1ad. The test unit supports both single-level Q-
frame and the two-level Q-in-Q-frame.
Table 6.2: C-VLAN and S-VLAN Selection
Field Description
VID match Enables selection by VID in the current filter. The value con-
figured here is used to determine which frames are allowed
to pass through the filter and which ones are blocked. The
available configuration values for this field are:
• Ignore: The VID is ignored and not taken into account for
the purpose of the filter. No frame is selected by the filter
when Ignore has been configured.
• Equal to: All frames matching a user configurable pattern
are allowed to pass through the filter. The matching pattern
is configured with the help of the VID field.
VID This setting contains a 10-bit identifier that constitutes the
VID value to be matched in the incoming traffic.
It is possible to match the S-VID or the C-VID through sepa-
rated entries in the filtering menu. For single-tagged frames it
is assumed that the frame does not contain S-VID field and
therefore configuration is done through the C-VLAN menu.