VPC subnets

Question 1

At what level are VPC subnets resilient?

Answer 1

At AZ level

Question 2

What happens to the VPC subnet if an AZ fails?

Answer 2

The subnet and services also fail.

Question 3

How many subnets per AZ can you have?

Answer 3

0 or more

Question 4

Can a subset CIDR range of the VPC overlap with any other subnet in that VPC?

Answer 4

No, it can’t overlap with any other subnets in that VPC

Question 5

Can you allocate an IPv6 CIDR block to a subnet?

Answer 5

Yes, but the VPC needs to be enabled for IPv6 beforehand.

Question 6

Can subnets in the same VPC communicate with each other by default?

Answer 6

Yes, isolation happens at the perimeter of the VPC

Question 7

How many reserved addresses exist in a VPC subnet?

Answer 7

5:

• VPC + 0: represents the network
• VPC + 1: VPC router
• VPC + 2: DNS
• VPC + 3: reserved for future AWS use
• Last IP in subnet: broadcast address.

Question 8

Is the broadcast address ever used by the VPC?

Answer 8

No.

Question 9

Where is DHCP configured in VPC?

Answer 9

In the VPC and it flows to all the subnets.

Question 10

What is DHCP?

Answer 10

Dynamic host control protocol. It is how computing devices receive IP addresses automatically.

Question 11

Can the DHCP options set be changed after configuration?

Answer 11

No, if you want to change the settings:

1. You have to create a new one
2. Change the VPC allocation to the new one
3. Delete the old one

Question 12

What does IP allocation options allow you to do?

Answer 12

1. Auto-assign public IPv4 addresses

2. Auto-assign IPv6 addresses - for this, VPC and subnet needs an allocation of IPv6 addresses beforehand