AWS SAA - VPC episode 1

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First, thanks to Don for the wonderful presentation method!

@ 5:32 mark, Don says that the smallest subnet you can make is /28 with 14 usable IP addresses.

/28 leaves 4 bits for the hosts (thanks Wes for the subnetting training!)
4^2 = 16 - 2 (network ID and broadcast) = 14, so I'm onboard with that.

But why can we not go with /29 or /30??
/29 = 3 bits left = 6 spots to use
/30 = 2 bits left = 2 spots to use

/31 would be useless. The 1 bit left leaves two hosts which are taken up by the network ID and broadcast address.

/32 I believe is used in AWS-land to specific a specific IP address, correct?

Also, does anyone know if the SAA course will be updated to cover the SAA-C02 objectives?

Blessed Easter!

@MichaelS,

Maybe @donpezet can correct me if I am wrong, but here it goes.

If you consult the FAQ(https://aws.amazon.com/vpc/faqs/) on the VPC service then you can see that the minimum size of a subnet is /28 for 14 addresses. This is a limit imposed by AWS though what you said could be possible in other situations.

Now part of the reason for this is that AWS reserves not just the first address but the first 4 addresses of a subnet as well as the last address. Thus a /29 would only have 4 addresses available. Now that might be enough for some applications, but that is just a recipe for disaster (my opinion) because of the additional reservations that AWS makes. So I suspect that Amazon just tries to keep shenanigans from happening.

Hope that helps.

Caveat Emptor: My calculations may be off.

Ya, I'm sure pretty sure that that is it, Justin. Thank you so much.

I tend to focus on one source at a time, otherwise I see the shiny thing on the internet while browsing amazon .com reading aws docs. And fwiw, I believe that /29 would give (2^3 - 5 reserved = 3 hosts available).