Return to Level1Techs.com

IPv4 Subnetting Question Answer


#1

Not sure if i am in the correct sub-cat here but its just a simple IPv4 Question that I need to be sure I have the right answer for:

Question: "Given a network address of 172.16.0.0/16, create 3 equal subnets to support 400 hosts each.

My answer:
Network Address : Net Mask (CIDR) : Broadcast Address : 1st Usable Host addr : Last usable Host Addr

172.16.0.0 , 20 , 172.16.15.255 , 172.16.0.1 , 172.16.15.254

172.16.16.0 , 20 , 172.16.31.255 , 172.16.16.1 , 172.16.31.254

172.16.32.0 , 20 , 172.16.47.255 , 172.16.32.1 , 172.16.47.254

Thank you in advance!


#2

Well, technically your answers are not incorrect. But commonly one would not provision a network the way you did.

Perhaps think a little bit smaller :wink:


#3

Okay thank you! It’s just a test question I’m doing but do not have the answer key for. Thanks! (:slight_smile:


#4

Your answers are fine. Your three subnets are within your /16 pool. They are of equal size. They don’t overlap. A subnet with a /20 mask has 4096 unique addresses, if you don’t want host addresses ending in .0 or .255, that leaves each subnet with 4064 unique addresses, which is more than enough for 400 hosts. And there is nothing “uncommon” about your subnets. It the exact way amazon provisions their default regional vpc’s /16 pool into 3 availability zones with /20 subnets.