Can someone check the subnetting answer here?

SurferdudeHB

What is the first valid host on the subnetwork that the node 172.21.32.229 255.255.255.240 belongs to?

Answer: 172.21.32.225

is this correct?

Got this from subquestion.com thx!

mens

yep, it's correct. Why?

240 means a 16 block (256-240=16)
224 is the corresponding subnet for address 229
225 is the first valid host for that subnet

SurferdudeHB

mens wrote: »

yep, it's correct. Why?

240 means a 16 block (256-240=16)
224 is the corresponding subnet for address 229
225 is the first valid host for that subnet

Thank you.

shednik

mens wrote: »

yep, it's correct. Why?

240 means a 16 block (256-240=16)
224 is the corresponding subnet for address 229
225 is the first valid host for that subnet

This is correct the best way to look for host ranges is to do the above 256-240 or look at the last bit of the mask. In this case was 16 then from there you know each net block is going togo up by 16.

choslet

Hi there folks,

I used to do the same calc to allocate the block size, ex. whatever - 256 = block size. Then I realized that block size it's exactly the 2 (exp) [host bit], getting rid of that rest calculation and calculating the block in the same way you do to check how many available subnets are according to the given subnet bits.

example...

class C subnetting:

NNNNNNNN.NNNNNNNN.NNNNNNNN.SSSHHHHH

2 exp H = block
2 exp S = subnets
(2 exp H)-2 = hosts, or block-2=hosts

definition: nibble byte/2 = 4 bit in a row... :P

Other helping strategies are working with nibbles , in the interesting bytein order to get the decimal subnet value easily meaning 4 (240) 4 (15).

In the example my interesting nibble its 1110 so 224 its easy to get, instead of memorize the whole eight bit values...

So i work fully binary to subnet and then make the decimal mask with my nibbles...

hope this helps somebody!