Exam 300-620 topic 1 question 214 discussion

Actual exam question from Cisco's 300-620

Question #: 214
Topic #: 1

Refer to the exhibit. An engineer is migrating legacy servers into the Cisco ACI environment. The requirement is to ensure that all endpoints and MAC addresses are learned properly in legacy and Cisco ACI switches. Which configuration set must be configured under the bridge domain called bd_360 to accomplish this goal?

A. L2 Unknown Unicast: Hardware Proxy
ARP Flooding: Disabled
B. L2 Unknown Unicast: Flood -
ARP Flooding: Enabled
C. L2 Unknown Unicast: Hardware Proxy
ARP Flooding: Enabled
D. L2 Unknown Unicast: Flood -
ARP Flooding: Disabled

Show Suggested Answer

Suggested Answer: B 🗳️

by Rododendron2 at May 12, 2023, 8:06 p.m.

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CiscoBoi

Highly Voted 1 year ago

When migrating from legacy network aka Brownfield to ACI, the ACI fabric initially behaves as a purely L2 network (network centric aproach which is our use-case here) and the BD config should be as following, to meet this standard: 1. Unicast Routing = disabled, this will ensure that we are still utilzing the default GW of legacy network 2. L2 Unknown Unicast should be set to Flood (this will flood in a BD which is expanded to embrace the loads coming from legacy network (typically vMotion loads). 3. ARP flooding should be set to enabled a well. So the correct answer is B.

upvoted 6 times

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asd248402

Most Recent 1 year ago

Selected Answer: B

B arp HW proxy is not suited for this scenario as the routing is outside ACI

upvoted 4 times

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thinqtanklearningDOTcom

1 year, 1 month ago

Selected Answer: C

I am not entirely sure if you need to have ARP flooding enabled or not. But clearly, per Cisco documentation you need Hardware Proxy. "By default, Layer 2 unknown unicast traffic is sent to the spine proxy. This behaviour is controlled by the hardware proxy option associated with a bridge domain: if the destination is not known, send the packet to the spine proxy; if the spine proxy also does not know the address, discard the packet (default mode). The advantage of the hardware proxy mode is that no flooding occurs in the fabric. The potential disadvantage is that the fabric has to learn all the endpoint addresses."

upvoted 2 times

thinqtanklearningDOTcom

1 year, 1 month ago

The capability to disable ARP flooding depends on the configuration of hardware proxy and IP routing as follows: ● If hardware proxy is turned off, then ARP flooding is on and cannot be turned off. ● If hardware proxy is turned on but IP routing is turned off, ARP flooding is on and cannot be turned off. ● If hardware proxy is turned on and IP routing is turned on, then you can disable ARP flooding. You may consider ARP flooding to be necessary because of silent hosts, but this is not completely true. It is true that disabling ARP flooding requires the mapping database to know the endpoint IP address, and for this IP routing must be turned on. But even if the endpoint had been silent, Cisco ACI can resolve the endpoint IP address by sending ARP messages from the subnet IP address of the bridge domain. This feature is called ARP gleaning, and it requires the bridge domain to be configured with a subnet IP address.

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Rododendron2

1 year, 1 month ago

Selected Answer: B

B please

upvoted 4 times

thinqtanklearningDOTcom

1 year, 1 month ago

It is not B. See my reason below.

upvoted 1 times

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