i have the following class B : 172.16.0.0 /16
i want someone to confirm that the solution is correct for the first 3 sub-networks :
we will take 4 bits to have 16 networks that can fit the request , so my new subnet mask is : 255.255.240 .0
now , the first three networks are (the magic number is 16 ):
First network : 172.16.0.0
first valid IP : 172.16.0.1
Last Valid IP: 172.16.15.254
Second network : 172.16.16.0
first valid IP : 172.16.16.1
Last Valid IP: 172.16.31.254
Third network : 172.16.32.0
first valid IP : 172.16.32.1
Last Valid IP: 172.16.47.254
so is this solution is correct for the first three subnets ?!
i have another question which : What is the full subnet mask for address 172.16.5.10/28?
My answer was : 255.255.255.240
but i have this friend that told this is not correct because class B can't have such subnet mask that goes with 28 bits for network !!!!
my answer was it's ok we can take up to 30 bits for the network and at least 2 bits for the host for every class(A,B,C) of the IPs because taking more than 30 bits (example: if take 31 bit for networks would resulting for the law 2^h-2 (so we have one bit left for the hosts h=1 ) ---> 2^1-2=2-2=0 and that's not possible to have 0 hosts per network !!! )
so please correct me again if i'm wrong or there is something i'm missing in the subnetting thing
thank you all , Kind regards