Free Cisco CCNA Training: Cost to Reach Root from this Bridge

In this Cisco CCNA Training video, we’ll be talking about the “cost to reach root from this bridge” value. The Spanning Tree Protocol (STP) considers the path which has the lowest cost-to-reach to be the best path. Every port is assigned a specific “cost” which is directly relative to its speed; the higher the speed, the lower the port cost. Along with the cost-to-reach, Bridge Protocol Data Units (BPDUs) will also contain the Bridge ID, which simply identifies which switch sent the Bridge Protocol Data Unit (BPDU.)

As we went over in the last video about Bridge IDs, I’ll further explain how Bridge IDs are handled and compared against other Bridge IDs.

As you’ll learn above, if the incoming root bridge BID is lower than that of the switch receiving it, the switch will start to announce that device (with the lower BID) as the root bridge. However, if the incoming BID is higher than that of the receiver, then the receiver will continue to announce itself as the root bridge. The process will continue until every device (or switch) has agreed on the root bridge.

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