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6/28/2007 page 18 of 145
Priority Tagging (QoS)
IEEE 802.1p priority tagging is supported for two classes of services along with bandwidth support per
priority level. Transparent mode is supported through configuration wherein if the field is set, the tag bits
are ignored. The User can configure up to 8 different priority levels per port. Also priority overriding
(overriding the tagged field) can be enabled or disabled by the user.
Virtual LAN
The switch provides support for setting up both tagged Virtual LANs and port based Virtual LANs. A port
may belong to any number of Virtual LANs. The VLAN membership of a station is determined by the
VLAN(s) that have been defined for the port to which the station is connected. If a station should move
from one port to another, it loses its current VLAN membership and inherits that of the new port it is
connected to.
A Default Virtual LAN exists to which a port, which is not a member of any other Virtual LAN, will
belong. This allows the switch to operate as a ‘normal’ Bridge when it is used in a network. A port is
automatically removed from the Default VLAN when it is reconfigured to belong to another Virtual LAN.
Using Tagged VLANs the switch has the ability to take non-tagged packets in some ports, add a VLAN tag
to the packet and send it out tagged ports on the switch. The VLANs can also be configured to accept
tagged packets in tagged ports, strip the tags off the packets, and send the packets back out other untagged
ports. This allows a network administrator to set up the switch so he can support devices on the network
that do not support VLAN Tagged packets. The administrator can also set up the ports to discard any
packets that are tagged or to discard any packets that are untagged based on a hybrid VLAN of both tagged
and untagged ports, and using the VLAN Ingress Filter on the switch.
The 7014 Series switch also has the ability to allow overlapping VLANs. Overlapping VLANs gives the
user the ability to have one or more ports share two or more VLAN groups. For more information and
examples on how this could be implemented please see our website’s technical documents.
Rapid Spanning Tree Protocol
The rapid spanning tree protocol as specified in IEEE 802.1D-2004 is supported. One Spanning Tree per a
unit is supported. Besides a Spanning Tree per VLAN is also supported.
The Rapid Spanning Tree Protocol (RSTP) supersedes the Spanning Tree Protocol (STP) which was
described in IEEE 802.1D-1998. The RSTP is used to configure a simply connected active network
topology from the arbitrarily connected bridges of a bridged network. Bridges effectively connect just the
LANs to which their forwarding ports are attached. Ports that are in a blocking state do not forward frames.
The bridges in the network exchange sufficient information to automatically derive a spanning tree.
RSTP allows for much quicker learning of network topology changes than the older STP. RSTP supports
new and improved features such as rapid transition to forwarding state. RSTP also sends out new BPDUs
every hello time instead of just relaying them. RSTP interoperates with older STP switches by falling back
to the older STP when the older BPDUs are detected on bridge ports. The user can also manually configure
bridge ports to use the older STP when desired.