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Bridging
4-62 Source Route Configuration
Spanning Tree Mode
Indicates how a port on the device will behave with an incoming single-route
broadcast (Spanning Tree ExplorerÑSTE) frame. You can conÞgure this Þeld with
the radio buttons and checkboxes, or via the MIBTools utility or local
management.
This Þeld allows you to conÞgure a Spanning Tree for your network. You can set
the Spanning Tree Mode to Auto or Manual using the radio buttons. We
recommend that all bridges in your network topology have the same setting for
Spanning Tree Mode (i.e., all set to Auto or all set to Manual).
Auto If the Spanning Tree Mode is set to Auto, a port that implements
the Spanning Tree Algorithm (STA), and is enabled and in the
forwarding state, will accept and relay STE frames onto its
attached segment.
Using STA, a bridge port will only forward frames if it is the
designated port for its attached segment. A port is ÒdesignatedÓ
for its segment if it has the lowest Root Path Cost of all bridge
ports attached to that segment. The Root Path Cost is the lowest
total path cost calculated by adding the costs of each port along
the path of a frame that traverses the bridge topology from the
root to that port (including its own path cost).
If two ports on a segment have equal Root Path Costs, the port on
the bridge with the highest priority bridge identiÞer (for
convenience sake, that have the lowest numerical value) will be
chosen as the root port.
You can affect Spanning Tree topology by changing the deviceÕs
bridge priority (Bridge Label) and path cost for its port pair (path
cost increment) via the Spanning Tree window (discussed in
earlier in this chapter).
Manual If the Spanning Tree Mode is set to Manual, you can manually
conÞgure the bridge to forward STE frames (i.e., manually
establish a Spanning Tree for STE frames by determining which
bridge in a parallel series of bridges will forward these frames).
If you set the Spanning Tree Mode to Manual, you can use the Enable or Disable
checkboxes to set a portÕs Spanning Tree Enable State to:
- Enabled (participating in frame relay).
- Disabled (not participating in the bridging process or in operation of the
Spanning Tree Algorithm and protocol). If the Spanning Tree Mode is set
to Disabled, the bridge port will not send or accept any STE frames. Any
STE frame received will be discarded. The Spanning Tree Expl Þeld at the
ConÞguration window, and the STE Frames Þeld at the Status window
will both read ÒDisabled.Ó