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Exam ANS-C00 topic 1 question 135 discussion

Exam question from Amazon's ANS-C00

Question #: 135
Topic #: 1

You have a DX connection and a VPN connection as backup for your 10.0.0.0/16 network. You just received a letter indicating that the colocation provider hosting the DX connection will be undergoing maintenance soon. It is critical that you do not experience any downtime or latency during this period.
What is the best course of action?

A. Configure the VPN as a static VPN instead of dynamic.
B. Configure AS_PATH Prepending on the DX connection to make it the less preferred path.
C. Advertise 10.0.0.0/9 and 10.128.0.0/9 over your VPN connection.
D. None of the above.

Show Suggested Answer

Suggested Answer: D 🗳️
A more specific route is the only way to force AWS to prefer a VPN connection over a DX connection. A /9 is not more specific than a /16.

by BlueGreen at Nov. 21, 2020, 6:18 p.m.

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Comments

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Scunningham99

Highly Voted 3 years, 7 months ago

D D D D D https://aws.amazon.com/premiumsupport/knowledge-center/configure-vpn-backup-dx/

upvoted 7 times

StelSen

3 years, 7 months ago

This is correct.

upvoted 1 times

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sapien45

Most Recent 3 years, 2 months ago

Solution would have been to advertise a higer CIDR on the VPN connection D

upvoted 1 times

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JamesTR

3 years, 7 months ago

B is not good. AWS will always prefer Direct Connect over VPN, regardless of AS path prepending https://aws.amazon.com/premiumsupport/knowledge-center/configure-vpn-backup-dx/

upvoted 2 times

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Huntkey

3 years, 7 months ago

B. D is incorrect. 10.0.0.0/16 is more specific than 10.0.0.0/9 and 10.128.0.0/9. In addition, you can use the more specific prefix for controlling traffic from the AWS, but not which path to use for sending to the AWS

upvoted 2 times

Huntkey

3 years, 7 months ago

Sorry I meant B is incorrect. D is the answer.

upvoted 1 times

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asiansensation

3 years, 8 months ago

D is the answer. If you are advertising the same routes toward the AWS VPC, the Direct Connect path is always be preferred, regardless of AS path prepending.

upvoted 4 times

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Souslik1999

3 years, 8 months ago

B is the solution

upvoted 2 times

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BlueGreen

3 years, 8 months ago

? B. Configure AS_PATH Prepending on the DX connection to make it the less preferred path.

upvoted 1 times

BlueGreen

3 years, 8 months ago

According to AWS "Be sure that Direct Connect is the preferred route from your end, and not over VPN when the Direct Connect virtual interface is up in order to avoid asymmetric routing; this might cause traffic to be dropped. We always prefer a Direct Connect connection over VPN routes."

upvoted 1 times

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