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Exam Professional Cloud Network Engineer topic 1 question 77 discussion

Actual exam question from Google's Professional Cloud Network Engineer
Question #: 77
Topic #: 1
[All Professional Cloud Network Engineer Questions]

After a network change window one of your company's applications stops working. The application uses an on-premises database server that no longer receives any traffic from the application. The database server IP address is 10.2.1.25. You examine the change request, and the only change is that 3 additional VPC subnets were created. The new VPC subnets created are 10.1.0.0/16, 10.2.0.0/16, and 10.3.1.0/24/ The on-premises router is advertising 10.0.0.0/8.
What is the most likely cause of this problem?

  • A. The less specific VPC subnet route is taking priority.
  • B. The more specific VPC subnet route is taking priority.
  • C. The on-premises router is not advertising a route for the database server.
  • D. A cloud firewall rule that blocks traffic to the on-premises database server was created during the change.
Show Suggested Answer Hide Answer
Suggested Answer: B 🗳️
by Jasonwcc at Nov. 8, 2020, 12:11 a.m.

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superpane
Highly Voted 4 years, 3 months ago
Sorry, correct is B, the more specific takes priority
upvoted 18 times
mikelabs
4 years, 3 months ago
I agree with you
upvoted 2 times
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lukedj87
4 years, 3 months ago
Agree! Apologise. I made confusion between answers. B is correct
upvoted 2 times
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pentium2000
Highly Voted 3 years, 10 months ago
The answer is B, Here is the routing table after the maintenance job 10.1.0.0/16 -> directly connected route 10.2.0.0/16 -> directly connected route 10.3..1.0/24 -> directly connected route 10.0.0.0/8 -> next hop is on-prem As you can see, routing is go "longest matched" method, so instance see 10.2.1.25 as a local network device. Solution 1. On-prem should announce more specific route rather than /8. 2. The theory of design the network is wired, why do you add a overlapping subnet on your vpc.
upvoted 8 times
rahulps
2 years, 5 months ago
Man.....You gave a real clarity on the answers. Thanks a lot. I was breaking my head here. So you mean to say that , a new ip 10.2.1.25 will be created when a new subnet 10.2.0.0/16 gets created in the VPC which takes more priority (0) then to the 10.2.1.25 ip addresses of the database server in the Onpremise. Thank s man
upvoted 3 times
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dragos_dragos62000
Most Recent 1 year, 1 month ago
Selected Answer: B
More specific takes priority, so answer is B
upvoted 1 times
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gcpengineer
1 year, 6 months ago
This Q seems wrong if subnet range of 10.2.1.0/24 already on prem how you create 10.2.0.0/16 subnet in cloud. the interconect or vpn will never accept that route
upvoted 5 times
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Wasamela
2 years, 1 month ago
Selected Answer: B
Think about the "Longest Match" routing algorithm which routers use to select the longest (prefix) match to determine the egress interface. Answer is B
upvoted 2 times
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pk349
2 years, 1 month ago
• B. The more specific VPC ***** subnet route is taking priority.
upvoted 1 times
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hyosung
2 years, 6 months ago
Selected Answer: B
B is correct answer
upvoted 2 times
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hyosung
2 years, 6 months ago
10.0.0.0/8 is part of 10.1.0.0/24 10.2.0.0/24 and 10.3.0.0/24, but, VPC network route priority is VPC higher than 10.0.0.0/8 so the answer is B
upvoted 3 times
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kumarp6
3 years, 1 month ago
Answer is : B
upvoted 1 times
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Morgan91
3 years, 4 months ago
B si correct answer. https://cloud.google.com/vpc/docs/routes#routeselection
upvoted 2 times
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superpane
4 years, 3 months ago
The on-prem router annonces 10/8. But that cannot be reached because subnet routes (more specific than 10/8) are getting prioritized over route coming from the VPN, so the DB can't be reached. So in that case is A, the problem is caused the more specific routes take priority
upvoted 3 times
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lukedj87
4 years, 3 months ago
The answer is A. The on-prem router annonces 10/8. But that cannot be reached because subnet routes (more specific than 10/8) are getting prioritized over route coming from the VPN, so the DB can't be reached.
upvoted 2 times
hjson821109
4 years, 3 months ago
I agree with A
upvoted 1 times
lukedj87
4 years, 3 months ago
Sorry, my comment was correct. But the answer is B. Local subnet VPC routes are MORE specific!
upvoted 4 times
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Jasonwcc
4 years, 3 months ago
Since router is advertising 10.0.0.0/8 that includes all the 3 subnets. Then I don't see how A,B,C is denying that. D is the answer
upvoted 3 times
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Community vote distribution
A (35%)
C (25%)
B (20%)
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