Switch Ports Roles for IEEE 802.1w Standard - Cisco Exam 200-125

Forwarding Traffic Roles

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Question

Switch ports operating in which two roles will forward traffic according to the IEEE 802.1w standard? (Choose two.)

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A. B. C. D. E.

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The IEEE 802.1w standard defines the Rapid Spanning Tree Protocol (RSTP), which is an updated version of the Spanning Tree Protocol (STP) designed to provide faster convergence in the event of network topology changes. RSTP operates by placing switch ports into one of several roles, each with a specific set of responsibilities in the spanning tree.

Of the options listed, the switch ports operating in the designated and root roles will forward traffic according to the IEEE 802.1w standard.

  1. Designated Port: A designated port is a switch port that has been chosen to forward traffic on a particular segment of the network. In a given network segment, there can be only one designated port. The designated port is responsible for forwarding traffic from non-root switches toward the root switch. When a designated port receives a BPDU (Bridge Protocol Data Unit) from another switch, it will compare the information in the BPDU to determine whether the other switch is better suited to be the root. If the other switch has a lower bridge ID or priority, the designated port will transition to the forwarding state.

  2. Root Port: A root port is a switch port that provides the best path back to the root bridge. Each non-root switch will have one root port, which is the port that provides the lowest-cost path to the root bridge. The root port is responsible for forwarding traffic from the non-root switch toward the root switch.

Ports operating in alternate, backup, or disabled roles do not forward traffic according to the IEEE 802.1w standard:

  1. Alternate Port: An alternate port is a switch port that provides a backup path to the root bridge in case the current root port fails. While an alternate port is in the blocking state, it will not forward traffic.

  2. Backup Port: A backup port is a switch port that provides a backup path to the designated switch in case the current designated port fails. Like an alternate port, a backup port is in the blocking state and does not forward traffic.

  3. Disabled Port: A disabled port is a switch port that has been administratively shut down and does not participate in the spanning tree.

In summary, only the switch ports operating in the designated and root roles forward traffic according to the IEEE 802.1w standard, as they are responsible for forwarding traffic toward the root switch and providing the best path back to the root bridge.