Broadcast Address.

Question

Consider a subnet mask 255.255.255.42 for a network 192.198.191. A data packet has arrived with destination IP as 192.198.191.121. The Broadcasting address of the subnet to which the packet belongs to is _____

Answer 1

121 = 0 1 1 1 1 0 0 1

42   = 0 0 1 0 1 0 1 0

Note the position of 1's in 42 and corresponding position in 121 keep them unchanged and make all other bits 1.

Ans = 1 1 1 1 1 1 0 1 = 253

directed broadcast addres=192.198.191.253

Comments

Got it! Thanks!

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Does the bit in position 2,4,6 belong to network ID of subnet?

Answer 2

42   = 0 0 1 0 1 0 1 0 

2^{(No. of  1s in mask)} = Total number of subnets.

In this case,

2³ = 8 subnets.

As by the concept of DBA, all host bits have to be 1.

121 = 0 1 1 1 1 0 0 1 

Here bits 2,4,6 from LSB represents subnet

So except 2,4,6  in 0 1 1 1 1 0 0 1 (121) change every other bits to 1.

We would get : 1 1 1 1 1 1 0 1 = 253​​​​​​​

So, DBA would be 192.198.191.253