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36 Intel® NetStructure™ ZT 8101 10/100 Ethernet Switch User’s Manual
Switch Management and Operating Concepts
The complexity of the VLAN configuration is hidden. The switch applies the following rules when
it creates the VLAN:
• Tagged frames are discarded. With port-based VLANs, frames are assumed to be untagged, so
that the VLAN members do not receive frames coming from another VLAN.
• VLAN ID is assigned using an internal algorithm. The switch allocates the largest free VLAN
ID that is smaller than 4095 (for example, 4094, 4093, 4092).
• The member port's PVID is assigned as the VLAN ID.
• A port can only belong to one port-based VLAN.
IEEE 802.1Q VLANs
IEEE 802.1Q VLANs have the following characteristics:
• Use filtering to assign packets to VLANs.
• Assume the presence of a single global spanning tree.
• Use an explicit tagging scheme with one-level tagging.
An IEEE 802.1Q VLAN is not as simple as a port-based VLAN, but it is also more flexible. You
can configure ports to be tagged, untagged, or forbidden.
• Untagged Member Port—Designates the port as an untagged member of the VLAN. When
an untagged packet is transmitted by the port, the packet header remains unchanged. When a
tagged packet exits the port, the tag is stripped and the packet is changed to an untagged
packet. If the port is attached to a device that is not IEEE 802.1Q VLAN compliant (VLAN-
tag unaware), then the port should be set to untagged.
• Tagged Member Port—Designates the port as a tagged member of the VLAN. When an
untagged packet is transmitted by the port, the packet header is changed to include the 32-bit
tag associated with the PVID (Port VLAN Identifier). When a tagged packet with a different
VID exits the port, the packet header is unchanged. If the port is attached to a device that is
IEEE 802.1Q VLAN compliant, (VLAN-tag aware), then the port can be set to tagged.
• Forbidden Port—Designates the port as not being a member of the VLAN and prevents
packets tagged with the VLAN’s VID from entering the port.
You can enable or disable the following per port for IEEE 802.1Q VLANs:
• GVRP
• Ingress Checking
GVRP
GVRP (GARP VLAN Registration Protocol) must be enabled globally on the switch before
individual ports can be enabled.
A global flag controls the switch's ability to participate in dynamically configured VLANs. If the
GVRP flag is enabled, ports can dynamically register to be a member of a VLAN. If the flag is
disabled, only statically configured ports can be members of VLANs.
The default value is disabled.