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Exam ANS-C00 topic 1 question 76 discussion

Exam question from Amazon's ANS-C00
Question #: 76
Topic #: 1
[All ANS-C00 Questions]

A Network Engineer is provisioning a subnet for a load balancer that will sit in front of a fleet of application servers in a private subnet. There is limited IP space left in the VPC CIDR. The application has few users now but is expected to grow quickly to millions of users.
What design will use the LEAST amount of IP space, while allowing for this growth?

  • A. Use two /29 subnets for an Application Load Balancer in different Availability Zones.
  • B. Use one /29 subnet for the Network Load Balancer. Add another VPC CIDR to the VPC to allow for future growth.
  • C. Use two /28 subnets for a Network Load Balancer in different Availability Zones.
  • D. Use one /28 subnet for an Application Load Balancer. Add another VPC CIDR to the VPC to allow for future growth.
Show Suggested Answer Hide Answer
Suggested Answer: D 🗳️
by HazemYousry at Sept. 27, 2019, 9:43 p.m.
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aviz
Highly Voted 3 years, 6 months ago
answer is C,It says million of users.Only NLB can do it.
upvoted 18 times
CloudTrail
3 years, 6 months ago
why cant ALB do it?
upvoted 1 times
tuberculat
3 years, 6 months ago
because NLB can do it.
upvoted 2 times
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Stec1980
Highly Voted 3 years, 6 months ago
It's a poor questions because the recommendation for ELB of any kind is that you provision nothing smaller than a /27, although in this case a /28 will do the job. I'd go with C because of the "millions of users" statement...NLB is best placed to deal with this sort of load, especially if concurrent.
upvoted 7 times
Kentik
3 years, 5 months ago
yeah, i agree
upvoted 1 times
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StelSen
3 years, 5 months ago
You are right. https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html
upvoted 2 times
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squeeze_talus0y
Most Recent 2 years, 7 months ago
Selected Answer: C
The minimum size of a subnet is a /28 (or 14 IP addresses.) for IPv4. Network Load Balancer provides both TCP and UDP (Layer 4) load balancing. It is architected to handle millions of requests per second and sudden volatile traffic patterns, and provides extremely low latencies. The above two statements rule out A, B and D
upvoted 1 times
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NSF2
3 years, 5 months ago
The correct answer lies between C and D of course. Of those two, D talks about application LB as well as adding another CIDR which I would go with. Adding a NLB for application servers in a different AZ doesn't make much difference for address exhaustion.
upvoted 2 times
ptpho
3 years, 5 months ago
We got 2 /28 multi AZ vs 1 /28 + 1 cidr. Both cidr mapped -> IP using are nearly the same while C ensure HA and ensure for millions of users
upvoted 1 times
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Huy
3 years, 5 months ago
Agree. This dump doesn't have good comments as others dumps.
upvoted 2 times
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yijetef290
3 years, 6 months ago
It says "application servers in >a< private subnet". One subnet. So why would we need a load balancer across two subnets? If we lose the AZ, the EC2 instances are not available so having an ELB in another AZ serves no purpose.
upvoted 1 times
inf
3 years, 6 months ago
Answer: C NLB - " If you enable cross-zone load balancing, each load balancer node distributes traffic across the registered targets in all enabled Availability Zones". Effectively double the number of connections possible to your backend fleet. Scale the fleet (even in a single AZ) accordingly. It's a question of throughput, not availability
upvoted 6 times
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kvirk
3 years, 6 months ago
C is correct
upvoted 2 times
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BillyC
3 years, 6 months ago
Answer is C for my,,,
upvoted 4 times
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2cool2touch
3 years, 6 months ago
A&B cant be correct as minimum subnet size in AWS is /28. NLB is clearly stated in AWS documents to support millions of connections per sec. ALB can just scale up so both are comparable. D says add another vpc cidr and suggests using single subnet. both are against best practice, you should have 2 AZs for a LB. Hence C is my answer
upvoted 4 times
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ohcan
3 years, 6 months ago
Every load balancer have to have at least to network interfaces so two subnets are needed, and if only the NLB support millions of user then the right answer is C. But i don't know why is not enough with a /29 instead /28.
upvoted 1 times
ohcan
3 years, 6 months ago
I was thinking, /28 provide 8 IP addresses but only 6 usable, and any LB service need at least 8 USABLE ip addresses, so it'll need /28 . I'm I right?
upvoted 1 times
DonaldCMLIN
3 years, 6 months ago
IT's AWS limintation, Ref. by below url ( https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Subnets.html ) The CIDR block of a subnet can be the same as the CIDR block for the VPC (for a single subnet in the VPC), or a subset of the CIDR block for the VPC (for multiple subnets). The allowed block size is between a /28 netmask and /16 netmask. Besiges that if mask /28, You hold 2^(32-28)=2^4=16, each subnet, AWS will take first 4 and last 1, so You can use only 16-4-1 = 11 IP(s)
upvoted 4 times
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TarunB
3 years, 7 months ago
for me it is D. You can not add /29
upvoted 1 times
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HazemYousry
3 years, 7 months ago
Answer is # A
upvoted 1 times
Stec1980
3 years, 6 months ago
You can't provision /29 subnets in a VPC so neither a or B can be correct
upvoted 3 times
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C (25%)
B (20%)
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