Jeremy’s IT Lab lecture video:
Day 13 - Subnetting (1)
Practical Networking’s Subnetting Mastery playlist
Personal Note
- The formula to calculate the number of usable addresses in a subnet is:
- 2n - 2 = X usable addresses.
- Where n is equal to the number of host bits available.
- If you don’t know the amount of host bits available, you can find n through this formula:
- 2(32-CIDR)
- Where CIDR is the prefix length you’ve been given.
Subnetting - 3rd Octet
PracNet Subnet guide - 3rd octet
PracNet Subnet Guide - 3rd Octet
Practical Networking’s Subnetting Mastery playlist
The /17 - /24 Range, AKA: 3rd octet Range
- Draw a fourth row for the cheat sheet that ranges from /24 to /17, written from RIGHT to LEFT
- When solving questions, don’t forget that you’re working with the 3rd octet of the IP address now, so we’ll be incrementing the group size in the 3rd octet of our IP addresses.
- Also, watch out for changes in the 4th octet when calculating Network IP, Broadcast IP and etc.
Examples
Link to original
Subnetting - 2nd and 1st Octet
PracNet Subnet guide - 2nd and 1st octets
PracNet Subnet Guide - 2nd and 1st Octets
Practical Networking’s Subnetting Mastery playlist
The /1 - /16 Range, AKA: 2nd and 1st octet Range
- Draw a fifth and sixth row for the cheat sheet than ranges from /16 to /9 on the fourth, and /8 to /1 on the sixth, written from RIGHT to LEFT
- When solving questions, be mindful of what octet you’re working on when incrementing. If it’s in the 2nd octet range then you’ll be working with the 2nd octet of the IP address, and likewise for the 1st octet
- Also, do watch out for changes on the other octets, the ones that are to the right of the octet you’re currently working on.
Examples
Special Problem
- This image contains a special problem.
- When solving, you’ll find that there’s no next network section, as we’re currently on the last possible subnet of the /2 prefix
- The answer is to the next network will be: n/a
Link to original
Next network is N/A
