Subnetting Question

Ravenclaw

I can find ranges, broadcast, and networks and usable hosts, but this question I don't understand. It maybe the wording, can some one provide a quick solution or point me in the right direction as to solve it.......much appreciated..

Regards

The answer is B



How many hosts could you put on each subnet of 176.77.0.0 if you used a mask of 255.255.255.240? How many subnets would you have created?




A
14 useable hosts. 2048 subnets.


B
14 useable hosts. 4096 subnets.


C
14 useable hosts. 8192 subnets.


D
16 useable hosts. 4096 subnets.

Node Man

When i see long masks such as 255.255.255.240, the first think i ask myself is if the subnet or host portion is borrowing bits from the other side.

In this case, the subnet side is borrowning 4 bits from the host side. So the host side has 4 bits or 16 hosts -2 so it has 14 useable hosts.

The subnet side has 12 bits, for 4096 subnets.

Ravenclaw

OK how do you figure out the 4096 for the subnets

and on a question like this is there a quick way to figure it out?

How many hosts could you put on each subnet of 1.0.0.0 if you used a mask of 255.255.248.0? How many subnets would you have created?

theodoxa

Ravenclaw wrote: »

OK how do you figure out the 4096 for the subnets

and on a question like this is there a quick way to figure it out?

How many hosts could you put on each subnet of 1.0.0.0 if you used a mask of 255.255.248.0? How many subnets would you have created?

I've memorized some of the subnet masks. So, I know anytime I see 255.255.255.240 or /28 that it increments in 16s. 16-2 (1 address is used for the subnet ID and 1 for the broadcast address, leaving 14 usable for hosts).

I've memorized [for the last octet]:

128 (/25) - Increments by 128
240 (/2 - Increments by 16
252 (/30) - Increments by 4 (Commonly used for Point-to-Point Links)

From these, it's not too difficult to work back or forwards to whatever mask you're given. Each whole octet multiplies the result by 256. So, let's say you had 255.240.0.0, it would support (16 x 256 x 256) - 2 or approximately 1 MILLION Hosts. 255.255.240.0 would support (16 x 256) - 2 or 4094 hosts. To get the number of subnets you need to know what class the address is. 176.77 would be class B, meaning that it uses 16 bits (or the first 2 octets) for the network portion. To figure the number of subnets you take (256 / increment) x 256 (for each 255 octet past the network portion). In this case, the 3rd octet is 255, so you would do (256 / 16) x 256 which would be (16 x 256) or 4096.

[EDIT]

1.0.0.0, mask 255.255.248.0

Increment: 8 in the 3rd Octet
Hosts: (8 x 256) (because the last octet is 0) - 2 = 2048 - 2 = 2046
Subnets: 1.0.0.0 is Class A, so only the 1st octet is used for the network portion. Because, the first 2 octets of the subnet mask are 255, you would have 256 x (256 / = 256 x 32 = 8192 subnets

Node Man

Ravenclaw wrote: »

OK how do you figure out the 4096 for the subnets

Memorization - 4096 is 2 to the 12th power. i didnt think i could learn it. but subnetting is going to put your multiplication skills thru the roof.

goldenlight

Remember there are 32 bits in a IP ADDRESS So We Have

N=16 We have 16 Host bits because its a Class B Network
S=12
H=4 Prefix-32

So 16+12+4=32

The Answer:
Using my powers of 2 I get HOST= 2^4-2====14
Subnet=2^12====4096

Ravenclaw

ok thanks for the input, looks i need to boost my multiplying power skills and commit to memory

JDex

Ravenclaw wrote: »

ok thanks for the input, looks i need to boost my multiplying power skills and commit to memory

It's a bit of a tangent, but I spent 3 hours doing the entire khan academy arithmetic section to scrape the rust off of old skills. Absolutely worth the time. Google it and sign up, then math until it says your ready. Stop before trig unless you're just enjoying yourself. I went ahead and started at basic additions (and you can skip the videos and just quiz your way till you need a refresher).