Managing the Hub 2-57
The SmartSwitch 2000 Chassis View
What is an 802.1Q Port-Based VLAN?
Switches that support the pre-standard IEEE 802.1Q draft specification for
port-based VLANs act by classifying frames into VLAN membership. Usually,
VLAN classification is based on tag headers (VLAN tags) in the headers of data
frames. The tag header is inserted into the frame directly after the Source MAC
address field. A four-byte field in the tag header is used as the VLAN identifier.
These VLAN tags are added to data frames by the switch as the frames are
transmitted and/or received by certain ports, and are later used to make
forwarding decisions by the switch and other 802.1Q switches. In the absence of a
VLAN tag, a frame is assigned VLAN membership according to the VLAN
configuration of the switch port that receives the frame.
About 802.1Q VLAN Configuration and Operation
An 802.1Q VLAN is defined by assigning it a unique identification number (the
VLAN ID) and an optional name. The VLAN ID is used to identify data frames
that originate from, and are intended for, the ports assigned to the VLAN. Up to
64 VLANs may be created, with VLAN IDs ranging from 2-4094. VLAN ID 1 is
reserved for the Default VLAN.
Ports on 802.1Q switches are assigned membership in a VLAN by associating a
VLAN ID with each port on the switch. The VLAN ID is combined with the port’s
identification (e.g., device X port X) to form the Port VLAN ID (PVID).
When 802.1Q is implemented for a SmartSwitch 2000 that has an HSIM-A6DP
installed, each LEC will be represented as an individual port which can be easily
assigned membership in a VLAN.
Once VLANs have been configured and activated, all frames with unknown
destination addresses (including broadcast, unknown multicast, and unknown
unicast frames) will be contained within the VLAN of their origin. The switch’s
Filtering Database tracks the associations between MAC addresses, VLAN
eligibilities, and port numbers, and is used to make forwarding decisions for
frames. All VLANs share a single Spanning Tree.
NOTE
When 802.1Q mode is initially activated on a device, all ports are associated with the
Default VLAN (VLAN ID 1). If a VLAN ID has not been assigned to a particular port
on an 802.1Q switch, any frames received from that port will be classified as belonging to
the Default VLAN.
NOTE
For SmartSwitch 2000 firmware version 4.00.08 and above, the number of LECs
supported by the HSIM-A6DP in 802.1Q mode is limited to 32.