3com 2928 Betriebsanweisung
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Because the Web interface is available only for port-based VLANs, this chapter introduces only
port-based VLANs.
port-based VLANs.
Introduction to Port-Based VLAN
Port-based VLANs group VLAN members by port. A port forwards traffic for a VLAN only after it is
assigned to the VLAN.
assigned to the VLAN.
Port link type
Depending on the tag handling mode, the link type of a port can be one of the following three:
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Access. An access port belongs to only one VLAN and usually connects to a user device.
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Trunk. A trunk port can join multiple VLANs to receive and send traffic for them. It usually connects
to a network device.
to a network device.
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Hybrid. A hybrid port can join multiple VLANs to receive and send traffic for them. It can connect
either a user device or a network device.
either a user device or a network device.
A hybrid port is different from a trunk port in that:
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A hybrid port allows traffic of multiple VLANs to pass through untagged.
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A trunk port allows only traffic of the default VLAN to pass through untagged.
Default VLAN (PVID)
By default, VLAN 1 is the default VLAN for all ports. However, you can change the default VLAN for a
port as required. When doing this, follow these guidelines:
port as required. When doing this, follow these guidelines:
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Because an access port can join only one VLAN, its default VLAN is the VLAN to which it belongs
and cannot be configured.
and cannot be configured.
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Because a trunk or hybrid port can join multiple VLANs, you can configure a default VLAN for the
port.
port.
A port configured with a default VLAN handles a frame as follows:
Actions (in the inbound direction)
Port type
Untagged frame
Tagged frame
Actions (in the outbound
direction)
Access
Tag the frame with
the default VLAN
tag.
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Receive the frame if
its VLAN ID is the
same as the default
VLAN ID.
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Drop the frame if its
VLAN ID is different
from the default
VLAN ID.
Remove the default VLAN tag and
send the frame.
Trunk
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Remove the tag and send the
frame if the frame carries the
default VLAN tag and the port
belongs to the default VLAN.
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Send the frame without removing
the tag if its VLAN is carried on
the port but is different from the
default one.
Hybrid
Check whether the
default VLAN is
carried on the port:
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If yes, tag the
frame with the
default VLAN
tag.
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If not, drop the
frame.
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Receive the frame if
its VLAN is carried
on the port.
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Drop the frame if its
VLAN is not carried
on the port.
Send the frame if its VLAN is carried
on the port. The frame is sent with
the VLAN tag removed or intact
depending on your configuration.