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Exam 300-420 topic 1 question 162 discussion

Actual exam question from Cisco's 300-420

Question #: 162
Topic #: 1

An engineer is designing a network for a customer running a wireless network with a common VLAN for all APs. The customer is experiencing unicast flooding in the Layer 2 network between the aggregation and access layers. The customer wants to reduce the flooding and improve convergence time. Which solution meets these requirements?

A. Migrate all APs to a common Layer 2 access layer switch and run Layer 3 from the aggregation layer to all remaining access layer switches.
B. Align HSRP primary and STP root bridges and reduce ARP timers to match CAM timers on the aggregation layer switches.
C. Migrate to a Layer 3 access campus design if the APs can run on separate VLANs.
D. Align HSRP primary and STP root bridges if the APs cannot run on separate VLANs.

Show Suggested Answer

Suggested Answer: B 🗳️

by Hope66 at Sept. 23, 2022, 7:27 a.m.

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Hope66

Highly Voted 2 years, 9 months ago

I think B The default ARP table aging time is 4 hours while the CAM holds the entries for only 5 minutes. The switch sends out a frame to all forwarding ports within the respective VLAN when the destination MAC address is aged out from the CAM table. You need a CAM aging timer greater or equal to the ARP timeout in order to prevent unicast flooding. https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/71079-arp-cam-tableissues.html#:~:text=The%20default%20ARP%20table%20aging%20time%20is%204,ARP%20timeout%20in%20order%20to%20prevent%20unicast%20flooding.

upvoted 15 times

rted

11 months, 3 weeks ago

But B says "reduce ARP timers to match CAM timers". The flooding will still happen at same interval.

upvoted 2 times

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adcym

Most Recent 5 months, 3 weeks ago

Selected Answer: B

Answer is B.

upvoted 1 times

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muffedtrims

7 months, 4 weeks ago

Selected Answer: B

Voting B based on Hope66 explanation.

upvoted 1 times

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Swiz005

9 months, 2 weeks ago

Selected Answer: C

Answer is C

upvoted 1 times

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beskar

1 year, 10 months ago

Selected Answer: C

L3 Access Layer design will eliminate STP along with providing better convergence times than traditional L2 design.

upvoted 3 times

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SomKeat

1 year, 10 months ago

Answer is B

upvoted 1 times

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CKL_SG

2 years ago

Selected Answer: B

Spanning-tree protocol looping behavior, including blocked links, slow convergence, asymmetric forwarding, and switch CAM and ARP table tuning to address unicast flooding https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/cisco-campus-lan-wlan-design-guide.html

upvoted 1 times

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XalaGyan

2 years, 4 months ago

Selected Answer: B

Answer B is correct based on explanations provided by Hope66

upvoted 1 times

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