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3 Answers

Best answer
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5 votes

First of all , we have to understand that it is a classless addressing (CIDR notation).So here the number of addresses in a network is determined by the mask which is used .In this case the mask used is '/16' , hence,

No of network bits = 16

And no of host bits = 16

So no of hosts fror each network = 216

Now given no of subnets in each network = 1024.

Just to add the 10 bits used for subnet is taken from host bits in order to divide the network into subnets and hence will be used for defining subnet number.

So no of bits masked in total due to subnetting = 16+10 = 26

Now for subnet no. we have 10 bits and hence remaining 6 for host in a subnet.

Now we are asked the first address of 1024th subnet.For that 

The 1st 10 bits = 11111111 11 (for subnet no)

      last 6 bits(for a given subnet which is 1024th subnet) = 000000 (since it will be the 1st address of subnet)

So on combining we get the last 16 bits as : 11111111 11000000   

The first 2 octet will remain the same since the subnet will belong to the original network only

So in dotted notation , the first address = 190.76.255.192/26 ["/26" bcoz now 26 bits are masked in total as mentioned earlier]

For last address , we set the last 6 bits to 1 as well

So in dotted notation , the last address = 190.76.255.255/26

Hence C) is the correct option.

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In this network 16 bits are for network id and 16 bits for host id. To make 1024 subnets we need 10 more bits. hence take 3rd octet(8 bits) and 4th octet(2 bits). now we have to find the 1st and last address of last subnet (1024th subnet). So, first two octets will remain same and now consider 3rd and 4th octet. - - - - - - - - . - - - - - - - - . - - - - - - - - . - - - - - - - - .  make all 10 bits 1 from 3rd octate and 4th octet. for remaining 6 bits from 4th octet make them 0 and 1 to get first and last address.

so finally we get 190.76.255.192/26 as first address for 1024th subnet and 190.76.255.255/26 as last address for 1024th subnet.

edited by
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In order to have 1024 subnets, 10 bits of host id portion of class B address is used. Therefore, for any address, first 26 bits specify the subnet id and last 6 bit specify the host id. Last subnet address is 190.76.255.192/26. First and last address of this subnet will have all 0's and 1's in host id part. So, option C is correct.
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amiteshKeshari asked Oct 23, 2023
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