Am i thinking VLSM korrekt here?

[Erik Hellberg]

Goodday,

I hope this ends up in the right place here. Otherwise, my apologies. I'm very new to networking and subnetting, and hope that someone here might have a few pointes on how to improve. The below example is just a example and not a real life use.

I need to segment my network into three subnets.
Subnet 1: 26 Hosts
Subnet 2: 10 Hosts
Subnet 3: 4 hosts

So i start with my largest subnet.
192.168.1.1 / 27 which gives me the hostrange 192.168.1.1 - 192.168.1.30

Then i move on with the second largest subnet.
192.168.1.32 / 28 which gives me the hostrange 192.168.1.33 - 192.168.1.46

And then the final subnet.
192.168.1.48 / 29 which gives me the hostrange 192.168.1.49 - 192.168.1.54

What i'm infuriatingly uncertain of is if i'm doing this correct. When i have the range for the first subnet, do i just take the next numeral after that subnets broadcast adress and create a new subnet? Or am i just thinking this wrong?

With regards,
Erik

[Martin L]

Looks Ok. VLSM is about blocks and Magic Number. you start with largest subnet per number of hosts. For 26 hosts u need to use block of 32 (32-2=# of available hosts), so, 1st block of 32 u used for 1st subnet. now, u ahve several blocks of 32 left. you can squeeze in 10 hosts into 2nd block but u need only 10 hosts, which falls into block of 16. Now, u have blocks of 16 left. you need 4 hosts, u must use block of 8 (not 4 cause of -2 hosts)

[Martin L]

see Magic number table on CLN and my pdf https://learningnetwork.cisco.com/docs/DOC-26938

[Erik Hellberg]

Then i'm guessing i'm doing it correctly, or at least i have the concept down of what it's about. I'm curious though; Doesnt this create conflicts?

If i keep using the 192.168.1.0/27 example, we'd get subnets on 32-step increases (32, 64 etc). But then i continue on with a new subnet on .32 which would've been the next subnet on /27. Doesn't this cause conflicts as they overlap, or does it "simply" create a new subnet from that point and forgets that it would've been the next for /27?

Darn that was hard trying to put into words. I hope i didn't make it to hard to read!