I feel I understand general subnetting overall, I can answer any questions that the site http://subnettingquestions.com/ gives me but I seem to have a understanding gap some where.
Say an ISP gives me an IP address range to use, ex: 165.48.10.1 - 165.48.255.255. Do they specifically give you address ranges like this? Or would they have given it as 165.48.0.0 - 165.48.255.255?
And if they do give out such a specific range of addresses, and I want to split those up into smaller subnets, and say I want 4 subnets so I do /18 as the mask to get 4 subnets and 16382 hosts per subnet I run into my confusion.
If the address they give out starts at 165.48.10.1, and if I can't use any address before that like 165.48.9.254, I would need to adjust my subnet mask so it starts at 10.1 instead of 0.0? But if I use just a /18 I don't see how I can start there.
I understand ANDing the address + the subnet mask, which is why it starts at 0, but how would it start at 0 if I'm given a specific range?
ANDing
165.48.10.1 /18
1 0 1 0 0 1 0 1.0 0 1 1 0 0 0 0.0 0 0 0 1 0 1 0.0 0 0 0 0 0 0 1
1 1 1 1 1 1 1 1.1 1 1 1 1 1 1 1.1 1 0 0 0 0 0 0.0 0 0 0 0 0 0 0
1 0 1 0 0 1 0 1.0 0 1 1 0 0 0 0.0 0 0 0 0 0 0 0.0 0 0 0 0 0 0 0 ANDed result
= 165.48.0.0 starting network id of first subnet, but then that is before the range they gave. (If they give out ranges like I said)
Hopefully I've made some sense here, I've only been studying networking for about a month and half now! Any links or explanations are appreciated!