0

I am redoing some VPC work that my predecessor did. I haven't setup a lot of networks, so I wanted to double check what I think makes sense isn't breaking some rule that I'm not familiar with.

What we currently have are four subnets broken up as:

subnet 01: 10.0.0.0/16

subnet 02: 10.2.0.0/16

subnet 03: 10.4.0.0/16

subnet 04: 10.6.0.0/16

To my untrained eye it seems like we're wasting half the ip space here if we continue to follow this pattern. I would like to change it to:

subnet 01: 10.0.0.0/16

subnet 02: 10.1.0.0/16

subnet 03: 10.3.0.0/16

subnet 04: 10.4.0.0/16

Is there any reason that I might run into an issue with this changed scheme?

Joshua Banton
  • 1
  • 3
    `1.` You haven't really changed anything. Your proposed networks are /16 just like the existing networks. `2.` Changing for the sake of change is never the right thing to do. `3.` Wasted space? How many ip addressed endpoints do you think you're going to have/need? How is the current scheme wasteful in that respect? `4.` You state that you haven't set up a lot of networks so maybe spend some more time thinking, planning, and understanding before making wholesale changes. – joeqwerty Dec 12 '18 at 21:58
  • To be clear, I need to change these networks anyway, I'm not only changing this one thing. I just wanted to make sure I wasn't changing it into a broken state. I have many more subnets to create, so I wanted to make this simpler, with room to create more in the future. – Joshua Banton Dec 12 '18 at 22:02

2 Answers2

3

You are using a prefix length of 16, so the first 2 octets (e.g. 10.1) are the network portion of the address.

I don't see what you would gain by making the change, you will still have 4 subnets, with 2^16 -2 usable host addresses.

Can you elaborate further on what your trying to achieve?

Nathan Foley
  • 56
  • 2
  • 9
  • I simplified the question quite a bit. These are 4 out of 20 AWS VPCs that I have, and they are further broken down into smaller subnets within those VPCs. The scheme is designed to setup different AWS VPCs in different regions within a development environment. So 10.0.0.0/12 is used for QA for example, and 10.0.0.0/16, 10.2.0.0/16, 10.4.0.0/16, 10.6.0.0/16 are used for 4 different VPCs in different AWS regions. With the idea that if new regions are needed there would be space for them. I was concerned that I wasn't understanding something about the space between the blocks. – Joshua Banton Dec 12 '18 at 21:34
1

The 10.0.0.0/8 network is free to use by anyone (by RFC 1918). So, if you're just using four /16 subnets out of the 256 possible, there's still way to go. Why would you need to save on free address space? Additionally, which four /16 you use doesn't matter - you can fill in the gaps any time you like (and it's smart to leave some reserve for later route aggregation).

If you want to improve your network you might want to consider reducing the subnets to /24 or so - /16 with 65k hosts is a really large broadcast domain.

Zac67
  • 10,320
  • 2
  • 12
  • 32