User's Guide

Bridging
89
As shown in the above table, the state determines if the bridge will allow the port to
transmit frames. If you disable the port, it is excluded from bridge operation altogether.
However, a port that is not disabled can be dynamically excluded by the Spanning Tree
algorithm (see “Spanning Tree” on page 89).
Topology Support.
Topology Support.Topology Support.
Topology Support. The bridge supports the topology by determining which ports are
‘eligible’ to transmit frames. The bridge enables each port and allows it to transmit
frames if all of the following conditions apply:
• The port that received the frame was in a forwarding state.
• The port eligible for transmission is in a forwarding state.
• The port eligible for transmission is not the same as the port the packet was
received on.
• The size of the MTU conveyed by the frame does not exceed the maximum
size of MTU supported by the LAN to which the port eligible for transmission
is attached.
The frame is discarded if the port does not meet the above conditions.
Spanning Tree
Spanning Tree allows the bridge to determine which ports to shut down (put in Block-
ing mode) to break any loops which may occur in the topology. It uses an algorithm
that figures out the best route and determines which ports will be included in the Span-
ning Tree. If the Spanning Tree algorithm sets the port state to Blocking, the port will
not allow duplicate frames which result from multiple paths (loops) in the active topol-
ogy of the bridge to be transmitted. If you disable bridging, you also disable Spanning
Tree, as it applies to the bridging function only. You can then set the ports manually if
Spanning Tree is disabled but bridging is enabled in 1.3.2 Bridge Port Configuration,
described in detail on page 92.