Summary

The web content explains the significance of the slash notation in IP addresses, which indicates the number of bits used for the network address, thus determining the range of assignable IP addresses within a network.

Abstract

The article demystifies the slash notation used at the end of IP addresses, such as /8, /16, or /24, for those without a background in computer science. It clarifies that this notation specifies the number of bits dedicated to the network portion of an IP address in an IPv4 address space, which consists of 32 bits in total. For instance, an IP address of 192.168.10.0/24 means the first 24 bits are fixed for the network address, leaving the remaining 8 bits for host addresses within that network. The article also provides practical examples of how these notations apply to virtual networks in cloud environments like Microsoft Azure Cloud, emphasizing the importance of understanding subnetting to avoid IP address overlaps.

Opinions

The author acknowledges that programming is more appealing to them than networking, which initially seemed daunting.
The necessity of understanding networking concepts is highlighted by the author's experience of being "pushed into developing in the Cloud," suggesting a learning curve for software developers venturing into cloud services.
The author implies that a clear understanding of the slash notation is crucial for architecting cloud solutions without causing network conflicts, such as overlapping IP addresses.
The article is tailored for software developers who may not have formal computer science education but need to grasp networking essentials due to their work in cloud computing.

What is the Slash Notation at the End of IP Addresses (/8, /16, /24)?

For those without a Computer Science Degree.

If you have a CS degree, you may want to pass on this elementary article.

No talk about masks or octets here.

But for those software developers who lack Computer Science fundamentals, and have ventured into the cloud or networking spaces, this may be a question you’ve left unanswered for a while now.

I know I did. Programming excites me. Networking scares me. But as I was pushed into developing in the Cloud (Azure specifically), I didn’t have a choice.

Ram, Memory, Throughput, Virtual Networks, Subnets, I/O, Gateways, etc. etc. Yikes.

So what’s up with that “/”

When it comes to IP addresses in the cloud we see things like 192.168.10.0/24 or 10.1.0.0/16. And often we have to make a decision when architecting cloud solutions.

So what does this number after the slash mean in simple terms?

Well, in an IPv4 address space, there‘s a total of 32 bits.

The number that comes after the slash tells us how many bits are part of the network address (and ultimately what is left over, we can assign).

Yeah, I know. Still confusing. Let me continue.

So let’s take the IP address 192.168.10.0/24.

The “/24” here indicates that the first 24 bits are part of the network address (192.168.10) leaving only the remaining 8 bits able to be changed for specific host addresses (0-254).

That means a “/16” leaves the remaining 16 bits (or last two numbers) free to use for specific addresses and a “/8” the remaining 24 bits to use.

For better clarification, here are all the possible addresses for each:

10.0.0.0/24: Includes ranges 10.0.0.1–10.0.0.254 (can assign the last number) 10.0.0.0/16: Includes ranges 10.0.0.1–10.0.255.254 (can assign the last two numbers) 10.0.0.0/8: Includes ranges 10.0.0.1–10.255.255.254 (can assign the last three numbers)

A Practical Example

Let’s say you choose 10.0.0.0/24 for a virtual network in Microsoft Azure Cloud. This means for that virtual network you will have available the ranges 10.0.0.1–10.0.0.254 (note that you can only assign/change the last digit in that V-Net).

Then you create a second virtual network using 10.0.0.0/8 which ranges from 10.0.0.1–10.255.255.254.

The problem here is that some addresses may overlap which could be a problem. For example, they both have the capability to use 10.0.0.8 which will not work.

However, let’s redo this situation and say you create one virtual network using 10.0.0.0/16 (ranging 10.0.0.1–10.0.255.254) and another using 10.1.0.0/16 (10.1.0.1–10.1.255.254), you will have no overlap.

Conclusion

So in summary, and in non-CS degree terms, the slash notation tells us how many bits are used in that address (we can't change), and ultimately what is left for us to assign out specifically.