Ethernet Bridge, STP/RSTP STP/RSTP and Provider Bridge Configuration
3. Select a designated port on each segment
For each LAN segment (collision domain), there is a designated port. The designated port has
the lowest cost to the root bridge. Designated ports are normally in the forwarding state to
forward and receive traffic to the segment. If more than one port in the segment has the same
path cost, the port on the bridge which has the lowest bridge ID is selected as a designated
port.
4. Active Topology Monitoring and Update
After STP determines the lowest cost spanning tree, it enables all root ports and designated
ports, and disables all other ports. Network packets are therefore only forwarded between
root ports and designated ports, eliminating any possible network loops. STP-aware devices
exchange BPDUs periodically. A new spanning tree is constructed when the bridged LAN
topology changes.
Once a stable network topology has been established, all bridges listen for Hello BPDUs
transmitted from the root bridge. If a bridge does not get a Hello BPDU after a predefined
interval (Max Age), the bridge assumes that the link to the root bridge is down. This bridge
then initiates negotiations with other bridges to reconfigure the network to re-establish a valid
network topology.
The STP Workspace
Several views are available for STP configuration, monitoring and analysis. Each view has a
dedicated set of monitoring and configuration buttons, where some of the options are
common to the different views (the left pane in each view shows how the view is accessed):
STP Ports Glance View - lists all the STP Ports and their attributes in tabular format and
provides various display and management options. In addition, the pane allows
performing and GROUP operations by selecting a number of ports on which the
operations are performed. The following buttons are available:
Refresh - updates the displayed data
Init Data - resets the data
Details (on page 5-26) - shows the configured and the actual information on a Bridge
and Port level for the selected port.
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