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Zorluk: OrtaSTP Port States and PortFast Benefits

A newly deployed workstation experiences network initial connection timeouts and fails to receive an IPv4 address allocation from the DHCP server upon booting up. A technician notes that the switch interface connected to the workstation takes 30 seconds to begin forwarding traffic due to standard 802.1D Spanning Tree Protocol (STP) state transitions. Which configuration change on the access interface resolves this issue, and what is its exact operational behavior?

  1. Enable PortFast on the access interface, allowing it to bypass the Listening and Learning states and transition immediately from Blocking to Forwarding.Cevap
  2. B
    Enable PortFast on all inter-switch trunk links to ensure that STP Topology Change Notifications (TCNs) are transmitted instantly throughout the Layer 2 domain.
  3. C
    Configure the STP bridge priority to a custom value of 4000 on the access interface to force the interface into an active forwarding state without STP timers.
  4. D
    Configure an ip helper-address on the Layer 2 access interface to suppress incoming STP BPDUs and allow immediate frame transmission.

Cevap

Enabling PortFast on the host access interface immediately transitions the port from Blocking to Forwarding by bypassing the 15-second Listening and 15-second Learning STP states.
Standard 802.1D STP transitions ports through Blocking, Listening (15s), and Learning (15s) states before entering Forwarding. On edge access ports connected to workstations, this 30-second delay causes DHCP requests to time out. Enabling PortFast allows the switch interface to transition immediately from Blocking to Forwarding, bypassing Listening and Learning states.

Adım Adım Çözüm

1
Identify the cause of the delay during host boot-up.
Standard IEEE 802.1D STP requires a port to spend 15 seconds in the Listening state and 15 seconds in the Learning state (total 30 seconds) before reaching Forwarding.
During this 30-second delay, the switch drops user data frames, causing host applications (such as DHCP client requests) to time out.
2
Determine the appropriate Cisco STP optimization feature for access ports connected to end devices.
Cisco PortFast is designed specifically for access ports connected directly to workstations, servers, or end-user hosts.
PortFast bypasses the Listening and Learning states, allowing the interface to transition directly from Blocking to Forwarding upon link up.

Anahtar Kavram

Cisco STP PortFast operation and state bypass mechanism
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STP Port States and PortFast Benefits

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