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Chapter 47: Port-based and Tagged VLANs
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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.