CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
R1# show running-config | section interface
interface GigabitEthernet0/0
no switchport
ip address 192.0.2.1 255.255.255.252
!
interface GigabitEthernet0/1
switchport mode trunk
spanning-tree guard root
!
interface GigabitEthernet0/2
switchport mode trunk
spanning-tree loopguard default
!
interface GigabitEthernet0/3
switchport mode access
switchport access vlan 10
spanning-tree portfast
spanning-tree bpduguard enable
!
R1# show spanning-tree root
VLAN0001
Root ID Priority 32769
Address 0001.1111.1111
This bridge is the root
R1# show interfaces status | include err-disabled
GigabitEthernet0/3 err-disabled
You are connected to R1, a multilayer switch acting as the STP root bridge. Configure Root Guard on the designated port toward R2 (G0/1), Loop Guard on the uplink port G0/2, and BPDU Guard on PortFast-enabled access port G0/3. After configuration, a superior BPDU is received on G0/1, causing it to be blocked by Root Guard; later, an unauthorized BPDU on G0/3 triggers err-disable. Troubleshoot and verify the expected port states.
R1# show running-config | section interface
interface GigabitEthernet0/0
no switchport
ip address 192.0.2.1 255.255.255.252
!
interface GigabitEthernet0/1
switchport mode trunk
spanning-tree guard root
!
interface GigabitEthernet0/2
switchport mode trunk
spanning-tree loopguard default
!
interface GigabitEthernet0/3
switchport mode access
switchport access vlan 10
spanning-tree portfast
spanning-tree bpduguard enable
!
R1# show spanning-tree root
VLAN0001
Root ID Priority 32769
Address 0001.1111.1111
This bridge is the root
R1# show interfaces status | include err-disabled
GigabitEthernet0/3 err-disabled
A
G0/1 is in blocking state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Root Guard forces a designated port to block if a superior BPDU is received, preventing an unauthorized root bridge. Loop Guard on G0/2 keeps the port in forwarding state as long as BPDUs are received; if BPDUs stop, it transitions to loop-inconsistent blocking. BPDU Guard on a PortFast-enabled access port places the port in err-disable state upon receiving any BPDU, protecting the edge port.
B
G0/1 is in forwarding state (Root Guard), G0/2 is in blocking state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Why wrong: This is incorrect because Root Guard does not allow the port to forward when a superior BPDU is received; it blocks the port. Loop Guard does not block the port immediately; it only blocks if BPDUs stop being received. Here, BPDUs are still being received, so G0/2 should be forwarding.
C
G0/1 is in err-disable state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in blocking state (BPDU Guard).
Why wrong: This is incorrect because Root Guard does not place the port in err-disable; it blocks the port while the superior BPDU is received, and the port recovers automatically when the superior BPDU stops. BPDU Guard places the port in err-disable, not blocking state.
D
G0/1 is in blocking state (Root Guard), G0/2 is in loop-inconsistent state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Why wrong: This is incorrect because Loop Guard only transitions to loop-inconsistent blocking state when BPDUs are no longer received. In this scenario, BPDUs are still being received on G0/2, so it remains in forwarding state. The question does not indicate a unidirectional link failure.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
G0/1 is in blocking state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
The root guard on G0/1 correctly blocked the port when a superior BPDU was received, preventing an unauthorized root bridge. Loop Guard was applied specifically to the uplink port G0/2 to prevent forwarding loops in case of uni-directional link failure. BPDU Guard on G0/3 placed the port into err-disable state upon receiving an unexpected BPDU, which protects the PortFast edge port. To restore G0/3, you must manually shut/no shut the interface after removing the offending device.
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.
✓
G0/1 is in blocking state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Why this is correct
Root Guard forces a designated port to block if a superior BPDU is received, preventing an unauthorized root bridge. Loop Guard on G0/2 keeps the port in forwarding state as long as BPDUs are received; if BPDUs stop, it transitions to loop-inconsistent blocking. BPDU Guard on a PortFast-enabled access port places the port in err-disable state upon receiving any BPDU, protecting the edge port.
Related concept
Static NAT maps one inside address to one outside address.
✗
G0/1 is in forwarding state (Root Guard), G0/2 is in blocking state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Why it's wrong here
This is incorrect because Root Guard does not allow the port to forward when a superior BPDU is received; it blocks the port. Loop Guard does not block the port immediately; it only blocks if BPDUs stop being received. Here, BPDUs are still being received, so G0/2 should be forwarding.
✗
G0/1 is in err-disable state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in blocking state (BPDU Guard).
Why it's wrong here
This is incorrect because Root Guard does not place the port in err-disable; it blocks the port while the superior BPDU is received, and the port recovers automatically when the superior BPDU stops. BPDU Guard places the port in err-disable, not blocking state.
✗
G0/1 is in blocking state (Root Guard), G0/2 is in loop-inconsistent state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).
Why it's wrong here
This is incorrect because Loop Guard only transitions to loop-inconsistent blocking state when BPDUs are no longer received. In this scenario, BPDUs are still being received on G0/2, so it remains in forwarding state. The question does not indicate a unidirectional link failure.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓G0/1 is in blocking state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).Correct answer▾
Why this is correct
Root Guard forces a designated port to block if a superior BPDU is received, preventing an unauthorized root bridge. Loop Guard on G0/2 keeps the port in forwarding state as long as BPDUs are received; if BPDUs stop, it transitions to loop-inconsistent blocking. BPDU Guard on a PortFast-enabled access port places the port in err-disable state upon receiving any BPDU, protecting the edge port.
✗G0/1 is in forwarding state (Root Guard), G0/2 is in blocking state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).Wrong answer — click to see why▾
Why this is wrong here
Root Guard blocks the port upon receiving a superior BPDU, not forwards. Loop Guard transitions to blocking only after BPDU loss, not while BPDUs are still received.
Why candidates choose this
Candidates may confuse Root Guard with BPDU Guard, thinking it err-disables, or think Loop Guard always blocks the port.
✗G0/1 is in err-disable state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in blocking state (BPDU Guard).Wrong answer — click to see why▾
Why this is wrong here
Root Guard results in a blocking state, not err-disable. BPDU Guard results in err-disable, not blocking.
Why candidates choose this
Candidates may think Root Guard err-disables because it's a security feature, or confuse the actions of Root Guard and BPDU Guard.
✗G0/1 is in blocking state (Root Guard), G0/2 is in loop-inconsistent state (Loop Guard), G0/3 is in err-disable state (BPDU Guard).Wrong answer — click to see why▾
Why this is wrong here
Loop Guard does not immediately place the port in loop-inconsistent state; it only does so after BPDU loss. Here, BPDUs are still being received.
Why candidates choose this
Candidates may think Loop Guard always puts the port in a special state, but it only activates upon BPDU loss.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
Trap categories for this question
Scenario analysis trap
This is incorrect because Loop Guard only transitions to loop-inconsistent blocking state when BPDUs are no longer received. In this scenario, BPDUs are still being received on G0/2, so it remains in forwarding state. The question does not indicate a unidirectional link failure.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
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 200-301 NAT questions on configuration and troubleshooting.
Switching and Network Access — This question tests Switching and Network Access — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: G0/1 is in blocking state (Root Guard), G0/2 is in forwarding state (Loop Guard), G0/3 is in err-disable state (BPDU Guard). — The root guard on G0/1 correctly blocked the port when a superior BPDU was received, preventing an unauthorized root bridge. Loop Guard was applied specifically to the uplink port G0/2 to prevent forwarding loops in case of uni-directional link failure. BPDU Guard on G0/3 placed the port into err-disable state upon receiving an unexpected BPDU, which protects the PortFast edge port. To restore G0/3, you must manually shut/no shut the interface after removing the offending device.
What should I do if I get this 200-301 question wrong?
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 200-301 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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