Exam 350-401 topic 1 question 142 discussion

Actual exam question from Cisco's 350-401

Question #: 142
Topic #: 1

Refer to the exhibit.

An engineer reconfigures the port-channel between SW1 and SW2 from an access port to a trunk and immediately notices this error in SW1's log:
*Mar 1 09:47:22.245: %PM-4-ERR_DISABLE: bpduguard error detected on Gi0/0, putting Gi0/0 in err-disable state
Which command set resolves this error?

A. SW1(config-if)#interface Gi0/0 SW1(config-if)#no spanning-tree bpdufilter SW1(config-if)#shut SW1(config-if)#no shut
B. SW1(config-if)#interface Gi0/0 SW1(config-if)#no spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut
C. SW1(config-if)#interface Gi0/0 SW1(config-if)#spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut
D. SW1(config-if)#interface Gi0/1 SW1(config-if)#spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut

Show Suggested Answer

Suggested Answer: B 🗳️

by [deleted] at May 9, 2021, 8:01 p.m.

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xziomal9

Highly Voted 3 years, 4 months ago

A. SW1(config-if)#interface Gi0/0 SW1(config-if)#no spanning-tree bpdufilter SW1(config-if)#shut SW1(config-if)#no shut B. SW1(config-if)#interface Gi0/0 SW1(config-if)#no spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut C. SW1(config-if)#interface Gi0/0 SW1(config-if)#spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut D. SW1(config-if)#interface Gi0/1 SW1(config-if)#spanning-tree bpduguard enable SW1(config-if)#shut SW1(config-if)#no shut The correct answer is: B

upvoted 13 times

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habibmangal

Most Recent 1 year, 9 months ago

the port has been connected to an unauthorized device or misconfigured. To resolve the error, BPDU Guard needs to be disabled on the interface and the interface needs to be brought out of the err-disable state. Option C is the correct set of commands to resolve this error as it enables BPDU Guard on the interface, which will prevent any unauthorized BPDU frames from being received on the interface, and then the interface is shut down and then brought back up. Option B is not the correct set of commands to resolve the error. This is because the "no" keyword is used with the "spanning-tree bpduguard enable" command, which would disable BPDU Guard on the interface. Instead, the "spanning-tree bpduguard enable" command needs to be omitted, and the "spanning-tree portfast disable" command needs to be used to prevent BPDU Guard from being triggered again on this interface

upvoted 1 times

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nushadu

2 years, 1 month ago

Selected Answer: B

tested: sw2(config-if)#spanning-tree bpduguard enable sw2(config-if)# *Dec 17 17:23:04.850: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port Et0/3 with BPDU Guard enabled. Disabling port. sw2(config-if)# *Dec 17 17:23:04.850: %PM-4-ERR_DISABLE: bpduguard error detected on Et0/3, putting Et0/3 in err-disable state *Dec 17 17:23:05.850: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0/3, changed state to down sw2(config-if)# *Dec 17 17:23:06.853: %LINK-3-UPDOWN: Interface Ethernet0/3, changed state to down sw2(config-if)# sw2#show interfaces status | i /3|Stat Port Name Status Vlan Duplex Speed Type Et0/3 err-disabled 1 auto auto unknown sw2#

upvoted 2 times

nushadu

2 years, 1 month ago

sw2(config-if)#do s runn interface e0/3 Building configuration... Current configuration : 74 bytes ! interface Ethernet0/3 duplex auto spanning-tree bpduguard enable end sw2(config-if)#no spanning-tree bpduguard enable sw2(config-if)#shutdown sw2(config-if)#no shutdown *Dec 17 17:30:52.608: %LINK-5-CHANGED: Interface Ethernet0/3, changed state to administratively down sw2(config-if)#no shutdown sw2(config-if)# *Dec 17 17:30:55.776: %LINK-3-UPDOWN: Interface Ethernet0/3, changed state to up *Dec 17 17:30:56.777: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0/3, changed state to up sw2(config-if)#

upvoted 1 times

nushadu

2 years, 1 month ago

sw2#show interfaces status | i /3|Stat Port Name Status Vlan Duplex Speed Type Et0/3 connected trunk auto auto unknown sw2#

upvoted 1 times

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timtgh

2 years, 8 months ago

Answer is correct, but this is a bad switch config because that port has portfast enabled and it shouldn't.

upvoted 4 times

timtgh

2 years, 8 months ago

The real proper solution would be disable portfast from all of those trunk ports. But that's not an option, so B is the best choice.

upvoted 3 times

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error_909

3 years, 4 months ago

Correct

upvoted 1 times

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SandyIndia

3 years, 5 months ago

Warning: Spantree port fast start should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc. to a fast start port can cause temporary spanning tree loops. (config-if)#spanning-tree portfast disable https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/69980-errdisable-recovery.html

upvoted 2 times

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