Exam N10-008 topic 1 question 312 discussion

▪ Root bridge ● Switch elected to act as a reference point for a spanning tree ● Switch with the lowest bridge ID (BID) is elected as the root bridge ● BID is made up of a priority value and a MAC address (with the lowest value considered root) -Jason Dion-

Mike Meyers "Using special STP frames known as bridge protocol data units (BPDUs), switches communicate with other switches to prevent loops from happening in the first place. Configuration BPDUs establish the topology, where one switch is elected root bridge and acts as the center of the STP universe. Each switch then uses the root bridge as a reference point to maintain a loop-free topology."

The switch with the lowest bridge ID

▪ Root bridge ● Switch elected to act as a reference point for a spanning tree ● Switch with the lowest bridge ID (BID) is elected as the root bridge ● BID is made up of a priority value and a MAC address (with the lowest value considered root)

From cisco.com: "As the BPDU goes out through the network, each switch compares the BPDU that the switch sends to the BPDU that the switch receives from the neighbors. The switches then agree on which switch is the root switch. The switch with the lowest ***bridge ID*** in the network wins this election process."

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/5234-5.html#:~:text=STP%20calculates%20the%20path%20cost,bridge%20becomes%20the%20root%20port

Right answer is A. When you learn how to configure stp, you will understand it well. I recommend the CCNA and CCNP Sw completed course. When you lhttps://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/5234-5.html#:~:text=STP%20calculates%20the%20path%20cost,bridge%20becomes%20the%20root%20port.

In the STP election process a switch port receives superior BPDUs from another switch and identifies that switch as the root bridge. The port with the lowest root path is selected as the root port, if possible.

Bridge Priority Data Unit (BPDU) – It contains the Bridge ID, Sender’s Bridge ID, Cost to the Root Bridge, Timer values on Root Bridge. All switches exchange BPDU in order to elect root bridge. The switch with the lowest Bridge ID become the root bridge.

This STP information is packaged as bridge protocol data unit (BPDU) multicast frames.

Though both the bridge ID and BPDU message are used in the election process I would choose bridge ID since it is closer to the actual election decision. The BPDU message is sent, received, then the bridge ID is extracted, bridge IDs are compared, and finally the election decision is made.

bridge ID

STP elects the root bridge based on the lowest bridge ID, which is a combination of a priority value and a MAC address. The lower the bridge ID, the higher the chance of becoming the root bridge

A, a bridge ID is used to select the STP root

It is A

From Exam Cram: STP uses bridge protocol data units (BPDUs) to identify the status of ports and bridges across the network. BPDUs are simple data messages exchanged between switches. BPDUs contain information on ports and provide the status of those ports to other switches. If a BPDU message finds a loop in the network, it is managed by shutting down a particular port or bridge interface.

geeksforgeeks ..... Bridge Priority Data Unit (BPDU) – It contains the Bridge ID, Sender’s Bridge ID, Cost to the Root Bridge, Timer values on Root Bridge. All switches exchange BPDU in order to elect root bridge. The switch with the lowest Bridge ID become the root bridge. Bridge ID – It is an 8-byte field that is a combination of bridge priority (2 bytes) and Base Mac address (6 bytes) of a device. If there is a tie on bridge priority then the Base Mac address is considered.