Subnet Question

thenjduke

I understand how to get the incrememnts of these subnets but my question is there a fast way to find what subnet this is instead of listing them all out.

Question: Which subnet does host 172.31.183.164/21 belong to?

Answer: 172.31.176.0

I have been multiplying for instance this is increments of 8 and I been doing 8 x 21. Just wondering faster way?

Neeko

I would just add from 160 since I know that is an incremend of 8.

thenjduke

Ahh did not even think about that. Also someone confirm this answer and why.
Question: You are designing a subnet mask for the 172.30.0.0 network. You want 1600 subnets with up to 22 hosts on each subnet. What subnet mask should you use?

I come up with 255.255.248.0 but answer is 255.255.224.0 and i am trying to figure out why.

dynamik

Wouldn't the answer be 255.255.255.224? Your default class B is 255.255.0.0, and you'll need 11 bits for the subnet mask (2048 subnets) and 5 for the hosts (30 hosts).

thenjduke

I figure it out.. I was taking from the network instead of the host on the formula I was using.. I will figure this out soon.

thenjduke

I was counting the wrong way.. I need to remember network and host

billscott92787

Question: You are designing a subnet mask for the 172.30.0.0 network. You want 1600 subnets with up to 22 hosts on each subnet. What subnet mask should you use?

I come up with 255.255.248.0 but answer is 255.255.224.0 and i am trying to figure out why.


Network Address: 172.30.0.0
Default Subnet Mask: 255.255.0.0


Bits needed 11 total bits ( 2^11=2048 ) This tells us that we need to borrow 11 bits.

So: 11111111.11111111.xxxxxxxx.xxx00000 -> X being the bits we need to borrow
Binary: 11111111.11111111.11111111.11100000

Result: 255.255.255.224 or /27 in bit notation


To determine the max number of hosts per subnet we would determine that there are 5 total host bits left. 2^5-2 = 30 total hosts per subnet because there is one reserved for the network address and one for the broadcast.