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Exam 300-420 topic 1 question 162 discussion

Actual exam question from Cisco's 300-420
Question #: 162
Topic #: 1
[All 300-420 Questions]

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.
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Suggested Answer: B 🗳️
by Hope66 at Sept. 23, 2022, 7:27 a.m.

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Hope66
Highly Voted 2 years, 3 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
6 months, 2 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 3 weeks, 2 days ago
Selected Answer: B
Answer is B.
upvoted 1 times
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muffedtrims
2 months, 3 weeks ago
Selected Answer: B
Voting B based on Hope66 explanation.
upvoted 1 times
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Swiz005
4 months, 1 week ago
Selected Answer: C
Answer is C
upvoted 1 times
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beskar
1 year, 5 months ago
Selected Answer: C
L3 Access Layer design will eliminate STP along with providing better convergence times than traditional L2 design.
upvoted 2 times
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SomKeat
1 year, 5 months ago
Answer is B
upvoted 1 times
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CKL_SG
1 year, 7 months 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
1 year, 11 months ago
Selected Answer: B
Answer B is correct based on explanations provided by Hope66
upvoted 1 times
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