Allied Telesis AT-S62 - Manual (Page 550)

Chapter 24: Port-based and Tagged Virtual LANs
550 Section V: VLANs
automatically assigns a PVID to a port, making it identical to the VID of the
VLAN to which the port is a member, when you assign the port as an
untagged member to a VLAN.
General Rules for
Creating a Port-
based VLAN
Below is a summary of the general rules to observe when creating a port-
based VLAN.
ˆ 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.
ˆ A port can be an untagged member of only one port-based VLAN at a
time.
ˆ Each port must be assigned a PVID. This value must be the same for
all ports in a port-based VLAN and it must match the VLAN’s VID. This
value is automatically assigned by the AT-S62 management software.
ˆ 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.
ˆ If there are end nodes in different VLANs that need to communicate
with each other, a router or Layer 3 switch is required to interconnect
the VLANs.
ˆ 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.
ˆ 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:
ˆ 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.
ˆ 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.