Allied Telesis AT-9000/28, User Manual

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Chapter 41: Port-based and Tagged VLANs
564 Section VII: Virtual LANs
Guidelines to
Creating a Port-
based VLAN
Below are the guidelines to creating a port-based VLAN.

Each port-based VLAN must be assigned a unique VID. If a particular
VLAN spans multiples switches, each part of the VLAN on the different
switches should be assigned the same VID.

A port can be an untagged member of only one port-based VLAN at a
time.

The PVID of a port is identical to the VID of the VLAN where the port is
an untagged member. The PVID value is automatically assigned by
the switch.

A port-based VLAN that spans multiple switches requires a port on
each switch where the VLAN is located to function as an
interconnection between the switches where the various parts of the
VLAN reside.

The switch can support up to a total of 4094 port-based, tagged,
protected ports, and MAC address-based VLANs.

A port set to the 802.1x authenticator or supplicant role must be
changed to the 802.1x none role before you can change its untagged
VLAN assignment. After the VLAN assignment is made, the port’s role
can be changed back again to authenticator or supplicant, if desired.

You cannot delete the Default VLAN from the switch.

Deleting an untagged port from the Default VLAN without assigning it
to another VLAN results in the port being an untagged member of no
VLAN.
Drawbacks of
Port-based
VLANs
There are several drawbacks to port-based VLANs:

It is not easy to share network resources, such as servers and printers,
across multiple VLANs. A router or Layer 3 switch must be added to
the network to provide a means for interconnecting the port-based
VLANs. The introduction of a router into your network could create
security issues from unauthorized access to your network.

A VLAN that spans several switches requires a port on each switch for
the interconnection of the various parts of the VLAN. For example, a
VLAN that spans three switches would require one port on each switch
to interconnect the various sections of the VLAN. In network
configurations where there are many individual VLANs that span
switches, many ports could end up being used ineffectively just to
interconnect the various VLANs.