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Management Guide
TigerAccess™ EE
8.1.6
SMC7824M/VSW
There are two methods for identifying the VLAN membership of a given frame:
Parse the frame and apply the membership rules (implicit tagging).
•
Provide an explicit VLAN identifier within the frame itself.
•
VLAN Tag
A VLAN tag is a predefined field in a frame that carries the VLAN identifier for that frame.
VLAN tags are always applied by a VLAN –aware device. VLAN-tagging provides a num-
ber of benefits, but also carries some disadvantages.
Advantages
VLAN association rules only need to be applied
once.
Only edge switches need to know the VLAN as-
sociation rules.
Core switches can get higher performance by
operating on an explicit VLAN identifier.
VLAN-aware end stations can further reduce the
performance load of edge switches.
Tab. 8.1
Advantages and Disadvantages of Tagged VLAN
Mapping Frames to VLAN
From the perspective the VLAN-aware devices, the distinguishing characteristic of a
VLAN is the means used to map a given frame to that VLAN. In the case of tagged frame,
the mapping is simple – the tag contains the VLAN identifier for the frame, and the frame
is assumed to belong to the indicated VLAN. That's all there is to it.
To configure the tagged VLAN, use the following command.
Command
vlan add VLANS PORTS tagged
VLAN Description
To specify a VLAN description, use the following command.
Command
vlan description VLANS DESC
no vlan description VLANS
Tags can only be interpreted by VLAN aware devices.
Edge switches must strip tags before forwarding
frames to legacy devices or VLAN-unaware domains.
Insertion or removal of a tag requires recalculation of
the FCS, possibly compromising frame integrity.
Tag insertion may increase the length of a frame be-
yond the maximum allowed by legacy equipment.
Mode
Configures tagged VLAN on a port:
Bridge
VLANS: VLAN ID (1-4094)
PORTS: port number
Mode
Specifies a VLAN description.
VLANS: VLAN ID (1-4094)
Bridge
DESC: description
Deletes a specified description.
Disadvantages
Description
Description
CLI
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