When using spanning tree protocol, which port on non-root bridges can forward traffic toward the root bridge?
a.
only one root port, which is the bridge's port that is furthest from the root bridge, can forward.
b.
only one root port, which is the bridge's port that is closest to the root bridge, can forward.
c.
all ports can forward frames to the root bridge, provided they are not in a down state.
d.
all ports will forward frames to the root bridge, unless a bpdu is received back on that same port.

b. Only one root port, which is the bridge's port that is closest to the root bridge, can forward.

Explanation:

Spanning Tree Protocol (STP) was architectured to avoid loops by finding redundant links in a network and closing them. To prevent loops in bridging redundant paths must be determined and blocked. Not only this protocol blocks redundant paths but it also activates them in case of a failure in the link.

Steps in the Spanning Tree protocol to select a root free topology:-

1. Elect one Root Bridge

2. Select one Root Port on the non-root bridges

3. Select one Designated Port on each segment

 In step 2

After selecting a Root Bridge all non-root Bridges elect a Root Port. This port has the lowest cumulative path cost towards the Root Bridge.

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