Question 1,212 of 2,015

Spanning Tree Protocol →mediumMultiple SelectObjective-mapped

Quick Answer

The correct answer is that RSTP eliminates the need for the Forward Delay timer by using a proposal-agreement handshake mechanism. Classic STP convergence relies on three timers: Hello (2 seconds), Max Age (20 seconds), and Forward Delay (15 seconds), where Max Age defines how long a switch waits without receiving a BPDU before re-evaluating the root, and Forward Delay governs the 15-second listening and learning states each. On the ENCOR 350-401 exam, this topic tests your understanding of why traditional STP convergence can take up to 50 seconds (20 sec Max Age + 15 sec listening + 15 sec learning) and how RSTP bypasses this delay through immediate port state transitions via handshakes. A common trap is confusing UplinkFast—a Cisco proprietary feature for root port failure recovery—with a standard STP timer; remember that only Hello, Max Age, and Forward Delay are the classic IEEE timers. Memory tip: think of the 2-20-15 rule for Hello, Max Age, and Forward Delay, and recall that RSTP’s handshake “skips the wait” by replacing Forward Delay with immediate agreement.

CCNP Spanning Tree Protocol Practice Question

This 350-401 practice question tests your understanding of spanning tree protocol. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Which three statements about STP convergence and timers are true? (Choose three.)

Question 1mediummulti select

Open the full STP breakdown →

A
The default Max Age timer in classic STP is 20 seconds.
Correct. Max Age defaults to 20 seconds, which is the time a switch waits to hear a BPDU from the root bridge before declaring it dead.
B
The Forward Delay timer determines how long a port stays in the listening and learning states, with a default of 15 seconds each.
Correct. Forward Delay is 15 seconds by default, and the port spends 15 seconds in listening and 15 seconds in learning, totaling 30 seconds.
C
RSTP eliminates the need for the Forward Delay timer by using a proposal-agreement handshake mechanism.
Correct. RSTP can transition ports to forwarding almost immediately using handshakes, bypassing the listening and learning states.
D
The Hello timer in STP is used to determine how often a switch sends BPDUs, with a default value of 5 seconds.
Why wrong: Incorrect. The default Hello timer is 2 seconds, not 5 seconds.
E
UplinkFast is a standard IEEE 802.1D feature that reduces convergence time after a root port failure.
Why wrong: Incorrect. UplinkFast is a Cisco proprietary feature, not part of the IEEE 802.1D standard.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The default Max Age timer in classic STP is 20 seconds.

Classic STP convergence relies on timers: Hello (2 sec), Max Age (20 sec), Forward Delay (15 sec). Max Age defines how long a switch waits without receiving a BPDU before re-evaluating the root. Forward Delay is the time spent in listening and learning states (each 15 sec). The total convergence time can be up to 50 seconds (20 sec Max Age + 15 sec listening + 15 sec learning). RSTP improves convergence by using handshakes instead of timers. UplinkFast is a Cisco proprietary feature that reduces convergence time after a root port failure, not a standard STP timer.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
The default Max Age timer in classic STP is 20 seconds.
Why this is correct
Correct. Max Age defaults to 20 seconds, which is the time a switch waits to hear a BPDU from the root bridge before declaring it dead.
Related concept
Static NAT maps one inside address to one outside address.
✓
The Forward Delay timer determines how long a port stays in the listening and learning states, with a default of 15 seconds each.
Why this is correct
Correct. Forward Delay is 15 seconds by default, and the port spends 15 seconds in listening and 15 seconds in learning, totaling 30 seconds.
Related concept
Static NAT maps one inside address to one outside address.
✓
RSTP eliminates the need for the Forward Delay timer by using a proposal-agreement handshake mechanism.
Why this is correct
Correct. RSTP can transition ports to forwarding almost immediately using handshakes, bypassing the listening and learning states.
Related concept
Static NAT maps one inside address to one outside address.
✗
The Hello timer in STP is used to determine how often a switch sends BPDUs, with a default value of 5 seconds.
Why it's wrong here
Incorrect. The default Hello timer is 2 seconds, not 5 seconds.
✗
UplinkFast is a standard IEEE 802.1D feature that reduces convergence time after a root port failure.
Why it's wrong here
Incorrect. UplinkFast is a Cisco proprietary feature, not part of the IEEE 802.1D standard.

Common exam traps

Common exam trap: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Real-world example

How this comes up in practice

A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

What to study next

Got this wrong? Here's your next step.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this 350-401 question test?

Spanning Tree Protocol — This question tests Spanning Tree Protocol — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: The default Max Age timer in classic STP is 20 seconds. — Classic STP convergence relies on timers: Hello (2 sec), Max Age (20 sec), Forward Delay (15 sec). Max Age defines how long a switch waits without receiving a BPDU before re-evaluating the root. Forward Delay is the time spent in listening and learning states (each 15 sec). The total convergence time can be up to 50 seconds (20 sec Max Age + 15 sec listening + 15 sec learning). RSTP improves convergence by using handshakes instead of timers. UplinkFast is a Cisco proprietary feature that reduces convergence time after a root port failure, not a standard STP timer.

What should I do if I get this 350-401 question wrong?

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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