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(Rapid) Spanning Tree
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– Rule 2: At least one active Spanning Tree component per loop
An active Spanning Tree component supports the Spanning Tree Protocol, sends/re-
ceives and evaluates BPDUs, and sets its ports to the relevant STP states.
Each loop in a network must have at least one active Spanning Tree component to dis-
integrate the loop.
Example:
Figure 5-12 Example topology
The loops in the example topology illustrated are disabled by active RSTP components. The
example topology contains three rings; the root and the backup root are components in
each of the three rings. The three rings do not affect one another; a modification to the to-
pology in one ring does not affect the topology of the other two rings.
–
Rule 3: No more than ten active Spanning Tree components in the topology
when using the Spanning Tree default setting
The ability to disintegrate any topology to form a tree without loops requires a complex
protocol that works with several variable timers. These variable timers are dimensioned
using the default values recommended by the IEEE standard so that a topology with a
maximum of ten active Spanning Tree components always results in a stable network.
When using large tree, please note the following (see also Section “Large tree support”
on page 111):
–
In the large tree support RSTP topology, only use devices that support large tree.
– Enable the “Large Tree Support” option on all devices.
– If RSTP is to be activated as the redundancy mechanism in an existing network
with more than seven switches along the relevant path, then the “Large Tree Sup-
port” option must first be enabled on all devices.
– It is recommended that “Large Tree Support” is not activated in networks with less
than seven switches along the relevant path.