A couple subnetting questions

[Ipsec Espah]

I'm doing some practice problems and theres a couple i'm not to sure about.

1. Which one of the following does not belong to the same subnet as the other three when using 255.255.224.0 as the subnet mask?

a. 172.16.66.24
b. 172.16.65.33
c. 172.16.64.42
d. 172.16.63.51

2. You are designing an IP addressing scheme for a large network with 4 subnets. You expect to add a subnet each year for the next 4 years? The network ID is 10.1.1.0. What subnet mask should you assign to allow for the maximum amount of hosts per subnet?

a. 255.0.0.0
b. 255.254.0.0
c. 255.240.0.0
d. 255.255.255.0

Any help is appriciated...

[YECoyote]

I don't want to give you the answer, so I'll give you these hints.

1. Look at the IP address to determine the IP class. Look at the SM to determine how many bits are borrowed. Once you have the class and know the bits borrowed, you can use this formula to go from 1 subnet to another: 2^(Max. host bits - bits borrowed). As an example, we have a class B with 4 borrowed bits. The subnet would be divided into groups of 16. The IP would then be 172.16.16.0 would be the 1st usable subnet. The IP 172.13.32.0 is the 2nd usable subnet. And so on, and so on.

2. This one is simply find what is the final number of subnets you want (hint: 4+1 per year). Use the formula 2^x > "wanted subnets" to find the number of borrowed bits. Then add from left to right the binary values of the borrowed bits. For example, you borrowed 3 bits, the SM will be 128+64+32 = 224.

Hope this is clear. I'm not a very good teacher.

[Ipsec Espah]

Yeah i get it now, thank you :cool: