Question

Need help with an IP exercise. If I have been given the IP network 146.127.144.0 from my ISP and I currently have 6 locations all about the same size.  

How do I figure out all the networks that could be assigned using CIDR format and their broadcast address.

I do not understand how to do this. I would appreciate a SIMPLE explanation. I am currently taking an introductory Networking course and I will be tested on this tomorrow.

Answer 1

As the requirement is of 6 subnet with equal number of hosts , Subnet mask that can provide 8 subnet will be used i.e 255.255.224.0 (/19)

note that number of subnets and number of hosts are in powers of 2 , therefore 8 subnets will be available.

( 2ⁿ =6 where n is approx 3.

therefore 3 bits will be borrowed from hosts bits

subnet mask (255.255.0.0) in binary (as given IP address is a class B IP address)=

 11111111.11111111.00000000.00000000

now, we want 3 bits from host bits therefore subnet mask in binary=

 11111111.11111111.11100000.00000000            (255.255.224.0)

As given IP address is of class B therefore /16 is default CIDR value and 3 bits will be borrowed therefore /19 will be used)

According to requirement , 6 subnets are required therefore 2 will be reserved for future use.

Now, subnetting given IP address 146.127.144.0 into 8 subnets with 8190 number of hosts in each subnet.

note tha first and last IP address are network ID and broadcast ID respectively and are not usable IP address.

therefore number of usable IP address are 2¹³=8192

8192-2=8190 (in each subnet))

and address space of 32.

CIDR	address space
24	1
23	2
22	4
21	8
20	16
19	32
18	64
17	128

subnet 1

first (usabe) IP address= 146.127.128.1

last IP address=146.127.159.254

broadcast IP address=146.127.159.255

subnet 2

first IP address= 146.127.160.1

last IP address=146.127.191.254

broadcast IP address=146.127.191.255

subnet 3

first IP address= 146.127.192.1

last IP address=146.127.223.254

broadcast IP address=146.127.223.255

subnet 4

first IP address= 146.127.224.1

last IP address=146.127.255.254

broadcast IP address=146.127.255.255

subnet 5

first IP address= 146.128.0.1

last IP address=146.128.31.254

broadcast IP address=146.128.31.255

subnet 6

first IP address= 146.128.32.1

last IP address=146.128.63.254

broadcast IP address=146.128.63.255