Networking - Networking Basics - Discussion

I didn't understand, please. Can anyone explain clearly.

I didn't understand. Can anyone explain me clearly please?

Actually the value given is wrong. the value should be 192.168.168.128

then only we can get the correct value.

192-128=64

so that we can get 64 values.that valid host range value should be between 129 to 191.

i think correct answer is B.

does anybody refuse it....?

Why the value should be between 129 and 191. It should be between 128-191. Also why the broadcast address is 191?

This value is right not wrong.
First of all we need to be the see the address and now.

We take broadcast address 256 then in this we subtract the value of last gourd subnet mask (192). Then we add the same bit of subtracting then we find the 128 also and then we re add the value (64) then we find out the 192 this will be the broadcast address of segment.

Here the subnet mask is 255.255.255.192 means only the last value is changing so subtract it from 255, you will get 64 means out of 255 IP's 64 is already used only 192 IP's are available.

256/4=64 means 0-63, 64-127, 128-191, 192-255 all 4 segments contains 64 IP's, out of which one segment is already used (lets not worry about it).

Now check the IP given which is 192. 168. 168. 188 which falls in the range 128-191 so here the valid host range will be from 129-190 because first one is always network IP, the last one is always the broadcast IP.

Subnet masks 255.255.255.192 means that it has 6 bits to represent hosts. which means in the last octet: first two bits represent network bits and other 6 host bits.

Now you are looking to fit 192.168.168.188.

Out of two bits you can have : either 10 or 11( 11 is not possible it will go beyond 192) so network bit is 10 , which makes it

128.( 255.255.255.128)

Now , possible values for hosts (for 6 bits) will start with: all zeroes to all 11s( but zero and all ones are meant for this network and broadcast)

Hence the possible values are: from 1 to 62

Which will be: 129 to 190

sbnet mask=255.255.255.{192} equiv to [11111111.11111111.11111111.11]00 0000 in binary. Now the binary values in [] represents the n/w portion i.e. first 26 bits is allocated for n/w portion and remaining 6 bits for the host portion.

Now take a look into the IP address.. 192.168.168.188 where the 1st 26 bits represent d N/W portion. So the binary representation of IP address is [11000000.10101000.10101000.10]111100,the bits in [] again representing the N/W portion.

There are four imp. things dat can be concluded from an IP address given with subnet mask,namely,
-> N/W ADDRESS
Represent d IP address in binary form and convert d HOST portion into ZEROS,and leave d N/W portion as it is. for eg. 11000000.10101000.10101000.10"111100" (192.168.168.188) is changed to 11000000.10101000.10101000.10"000000"(192.168.168.128;represents d n/w address). NOTICE THE CONVERSIONS REPRESENTED BY ".."

->1ST USABLE ADDRESS
The next IP address immediately after the N/W address is d 1st usable address. For eg. 192.168.168.129 is the 1st usable address in this case.

->LAST USABLE ADDRESS
Note that d host portion is of 6 bits i.e.2^6(=64) hosts can be connected. So d host portion can be divided in 64 blocks each i.e 0-63,64-127,128-191..and so on. Here in this case,since the n/w add. started from .128 so it must end on .191. So the LAST USABLE IP ADDRESS IS THE IP ADDRESS WHICH COMES IMMEDIATELY BEFORE THE BROADCAST ADDRESS. So the last usable IP address is 192.168.168.190.

->BROADCAST ADDRESS
It refers to d last IP address of the block. In this eg, the broadcast address is 192.168.168.191 since d block is 128-191 as seen in the previous step.

I hope u must have understood clearly.

192.168.168.188 255.255.255.192
mask 26.

And now have to find first address,
Applying AND operation with first address.

192.168.168.188
8 8 8 2

188 = 10111100.
And last 2 bit of mask,
11.

Hence first address,
192.168.168.128.

And last address,

Adding complement of mask into first address.

00000000 00000000 00000000 0011111111.
(63).

Since 1 address 192.168.168.128.

+ 0 0 0 63.

192.168.168.191.

I don't know that how we can find the IP address so please explain in details?