I'm preparing for an exam and I've come across a question that's a bit confusing. In most examples I've seen, the main network address is typically subnet 0. However, in my case, the main network address (which is a third octet in octal) doesn't start from 0; it's actually 172.16.20.0. I'm wondering if it's possible for the main network address to actually be another subnet, like subnet 5, especially since this example seems to imply that starting from subnet 0 might lead me to needing over 255 addresses with a /16 mask. ChatGPT suggested I could start from 172.16.0.0 instead, but I'm looking for some clarification on whether this is correct and what it means for subnetting. Any insights would be greatly appreciated!
5 Answers
Absolutely, the main network address can vary depending on your subnet mask. For example, many home networks use a common address like 192.168.1.0 with a mask of 255.255.255.0. However, you could split that network, like using 192.168.1.0 with a subnet mask of 255.255.255.127, creating another subnet at 192.168.1.128. So in your case with 172.16.20.0, you're not bound to starting at subnet 0 as long as your subnetting makes sense based on the mask you're using.
It really does hinge on your subnet mask. With a /16 mask, your primary address is indeed 172.16.0.0, but a /24 mask gives you a range from 0 to 255 for the subnet addresses. You might find it really useful to experiment with a visual subnet calculator to grasp how various numbers work in terms of subnets and masks. Here's a great one you can play with: [Subnet Calculator](https://www.davidc.net/sites/default/subnets/subnets.html).
For my example, I'm dealing with 172.16.20.20 and I have a mask of 255.255.0.0.
The terminology you're using might be throwing you off a bit. It's worth checking out some visual aids to get a better grasp. Here are some handy links for subnet masks: [Subnet Mask Cheat Sheet](https://www.aelius.com/njh/subnet_sheet.html) and [Subnet Calculator](https://www.calculator.net/ip-subnet-calculator.html). You can enter an IP, choose your subnet mask, and hit calculate. Just ignore the Network Class part!
Here’s an example I've translated and refined: 172.16.20.20/16 (255.255.0.0) needs to be subnetted into at least 60 subnets with the minimum borrowed bits. Please show your solution step by step and detail the new subnet mask. Identify the network address for this IP and provide the first and last host IPs for the first, second, and last subnets.
Just to clarify, it sounds like you want to break 172.16.20.0 into 64 subnets. You'd be looking at 172.16.20.0/30 for that. Can't quite wrap my head around why you’re placing the main network address in subnet 5, though. Double-check your calculations; it sounds doable!
For the mask I have, I'm using /16.
I don't do a ton of subnetting, but you really need to know your subnet mask. That is what determines how many usable IPs you have within your network range. Doing a bit of research on CIDR notation might provide some clarity on this topic!
In my case, it's /16.
In my situation, I'm working with 172.16.20.20 and I'm using a 255.255.0.0 mask.