IPv4 Subnetting Game for Networking Students

This is a work in progress, but here's something for networking students, network engineers, and IT professionals (yes, that includes you, networking nerds! 😉). How about a game for mastering IPv4 subnetting—computing subnet addresses, subnet masks, broadcast addresses, and first/last usable host addresses?

Ask and ye shall receive: chriv.github.io/ipv4-subnetting-browser-game

If you're wondering how the chart at the top works, here's a simple, non-binary approach to subnetting that anyone can use, using the example 10.189.174.5/23 in the screenshot.

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Compute the Subnet Mask:

IP addresses and Subnet masks are 32-bits long, written as 4 8-bit octets separated by dots. The CIDR prefix (e.g., /23) determines the boundary between the network bits and the host bits. CIDR stands for Classless Inter-Domain Routing, but I'll spare you the lecture on classful vs. classless networks/subnets.

• Octets to the left of the transition point are fully 255 (all network bits).
• Octets to the right of the transition point are fully 0 (all host bits).
• Only the transition octet will have a value other than 0 or 255.

1. Find the CIDR value, /23. It lands in the 3rd Octet. This is our transition octet.
2. The "Mask" row for /23 shows 254 in that 3rd octet.
3. Subnet Mask: 255.255.254.0

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Compute the Subnet Address:

The subnet address is the first IP address on a network. It is reserved and identifies (together with the subnet mask) the subnet; it cannot be used for a host/node on the network. The left part of an IP address is the network portion, while the right portion is the host portion.

1. Look at the "Bits" row for /23—the value is 2. This is our block size (or subnet increment) for the 3rd octet. The subnet will start on a multiple of this number in this octet.
2. 1st and 2nd Octets: Copy them (10.189.).
3. 3rd Octet: Find the closest multiple of 2 (our block size) that is less than or equal to 174. In this case, 174 is a multiple of 2.
4. 4th Octet: Set to 0. Subnet Address: 10.189.174.0

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Compute the Broadcast Address:

Every subnet has two reserved addresses. The last address is the broadcast address. To find it, first find where the next subnet starts.

1. For 10.189.174.0/23, the next subnet starts at 10.189.176.0 (adding our block size of 2 to the 3rd octet).
2. The broadcast address is the IP address immediately preceding the start of the next subnet. Broadcast Address: 10.189.175.255

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Figure out the First and Last Usable Host Addresses:

The subnet address (first IP) and broadcast address (last IP) cannot be used for hosts.

1. The first usable IP is one more than the subnet address (10.189.174.1).
2. The last usable IP is one less than the broadcast address (10.189.175.254). Usable Range: 10.189.174.1 - 10.189.175.254

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Let me know if you try the game! What's the hardest subnet you've encountered?

#networking #ipv4 #subnetting #cisco #itcareers