The official guide clearly specifies:
After PortFast is configured and a port is activated, the port immediately transitions from the blocking state to the forwarding state.
In a valid PortFast configuration, BPDUs should never be received because receipt of a BPDU indicates that another bridge or switch is connected to the port, potentially causing a spanning tree loop.
A. Fast convergence after a link failure: This is a feature of RSTP (Rapid Spanning Tree Protocol). While PortFast reduces convergence time for a single switch port, it does not accelerate convergence for the entire network after a link failure.
Correct answer is A&C
[C] is the basic principle of PortFast. OCG P235: "PortFast allows a switch to immediately transition from blocking to forwarding"
[A] is a feature of PortFast, as stated on the same page of OCG: As you might guess from the fact that PortFast speeds convergence, RSTP includes PortFast. You might recall the mention of RSTP port types, particularly point-to-point edge port types, around Figure 9-11. RSTP, by design of the protocol, converges quickly on these point-to-point edge type ports by bypassing the learning state, which is the same idea Cisco originally introduced with PortFast.
[D] is incorrect. Receiving BPDUs itself does not break things or create loops. The only difference between enabling PortFast and not enabling it is whether the port listens for a while before turning into forwarding state. With PortFast enabled, it turns into forwarding state immediately. If a loop is formed at this stage, STP will still react normally and block the port (prune this branch of the spanning tree).
Explanation:
A is correct because PortFast is designed to accelerate STP convergence, which helps speed up the transition to the forwarding state after a link failure.
C is correct because PortFast-enabled ports skip the traditional STP states (listening and learning) and move directly to the forwarding state, making convergence faster.
Incorrect options:
B: PortFast is not meant for uplinks to other switches, as it’s primarily for ports connecting end devices.
D: While PortFast ports don’t expect BPDUs, they still listen for them; if BPDUs are received, PortFast disables itself to avoid loops.
E: PortFast doesn’t detect indirect link failures; this is a feature of mechanisms like BackboneFast or other STP optimizations.
Ports Transition Directly to Forwarding State:
PortFast allows a switch or trunk port to enter the forwarding state immediately, bypassing the listening and learning states. This feature is useful for edge ports connecting to end devices, such as workstations or servers12.
Fast Convergence After Link Failure:
When a link fails, PortFast helps achieve rapid convergence by skipping the usual STP transitional states. This minimizes the time devices connected to the port must wait for network connectivity1.
Therefore, options C and A are the correct features of PortFast.
C & D are correct
PortFast is usually configured on an edge port, which means the port should not receive any STP BPDUs. If the port receives any STP BPDU, it moves back to normal mode and will participate in the listening and learning states.
A is UplinkFast
https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/catalyst9500/software/release/17-1/configuration_guide/lyr2/configuring_optional_spanning_tree_features.html#concept_pm2_j35_jgb
There is much misinformation about the operational details of PortFast circulating throughout the Internet. One of the most common misconceptions is that PortFast effectively disables STP, and BPDUs are no longer sent or received on the port. Everything about this statement is wrong. Not only does a PortFast-enabled port transmit BPDUs, but the operational PortFast status is actually dependent on incoming BPDUs. If the port receives BPDUs, the PortFast feature is disabled. Now, it is important to understand the difference between the administrative and operational state of PortFast. The administrative state refers to what is configured on the device, and the operational state defines whether the feature is actually enabled or disabled. There are basically two ways to enable PortFast: globally (spanning-tree portfast default) or per interface (spanning-tree portfast). Both commands enable PortFast on operational access ports. For example, a port that is administratively configured to negotiate a trunk but failed to do so would operate in access mode.
I originally went with A and C, but I changed my mind because "link failure" isn't relevant to edge-ports. Convergence after link failure is a feature of UplinkFast and BackBone fast; PortFast is designed to connect to end devices, or switches that connect to end devices.
Indeed, D is correct; to quote Cisco:
"the operational PortFast status is actually dependent on incoming BPDUs. If the port receives BPDUs, the PortFast feature is disabled"
So the port *does* operate normally without receiving BPDUs; it's only when it does receive them that it ceases to operate as desired.
Read the source carefully; people are using it to discount D, but it actually does the opposite.
https://learningnetwork.cisco.com/s/blogs/a0D3i000002SKQwEAO/advanced-stp-features-portfast-bpdu-guard-and-bpdu-filter
You have found the correct answer
A - UplinkFast
B - Loop guard
C - Portfast
D - Portfast (port is connected to end device, so no BPDU from the end device to the port)
E - BackbonFast
Letter D is correct. Ports with PortFast DO NOT operate normally when receiving BPDUs. "They operate normally WITHOUT receiving BPDUs". If the port receive any STP BPDU, it will revert to normal/regular mode and participate in listening and learning states. (letter A and D is correct).
https://www.arubanetworks.com/techdocs/ArubaOS_80_Web_Help/Content/ArubaFrameStyles/Network_Parameters/Portfast%20and%20BPDU%20Guard.htm#:~:text=If%20the%20port%20receives%20any%20STP%20BPDU%2C%20it%20moves%20back%20to%20normal/regular%20mode%20and%20will%20participate%20in%20the%20listening%20and%20learning%20states.
Letter C is wrong because I believe that when a port is in blocking state it is probably participating in the STP topology, thus receiving BPDUs, in this case as seen in the link, the PortFst feature is disabled when receiving BPDUs, so letter C is wrong. I also believe that in some questions you mention that with PortFast enabled on the interfaces, loops and storms can occur, but if I am right, this would only happen if all the other ports in the STP topology would also have PortFast enabled, in this case as there would be none BPDU on the network, so just in this case STP would not be enabled (keeping PortFast), just then loops and broadcast storms would occur.
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