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So there's a problem that literally stress me out every time I look at it. It's like I almost understand it until I get to knowing how to find the first and last host in the LAST address (last subnet).

My given address is 130.56.0.0/16. But I need 1024 subnetworks and create subnetworks with equal amount of hosts. I need to find:

  • Subnet mask
  • Number of addresses for each subnet
  • First and last address in the FIRST SUBNET
  • First and last address in the LAST SUBNET

Finding the first and last address in the LAST SUBNET is what terribly confused me

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So you have a /16 network and you need to divide it into 1024 subnets.

1024 = 2^10. That means on top of the /16, you use 10 bits to identify the subnet.

The consequence is that those subnets are /(16+10) = /26 networks

This leave you with 32-26 = 6 bits for the hosts.

So you have 2^6 = 64 addresses per subnet, including the network and broadcast addresses.

So the last byte of your network address, expressed in decimal, will always be a multiple of 64 (including multiplying by zero) so for examples :

130.56.0.0/26.
130.56.0.64/26.
...
130.56.17.128/26.
...
130.56.24.192/26.
...

And the broadcast address will always have the last byte equal to 63, 127,191,255

If we speak about usable host address, the first are always 1 / 65 / 129 / 193 (network address +1) and the last one 62, 126, 190, 254 (broadcast address -1).

The first subnet is quite straightforward: 130.56.0.0/26 with

  • network address 130.56.0.0
  • first usable host address 130.56.0.1
  • last usable host address 130.56.0.62
  • broadcast address 130.56.0.63

The last subnet is the one that end (broadcast address) with 255.255, so it is 130.56.255.255. Since we know its size (64) we can deduce the network address. This give

  • network address 130.56.255.192
  • first usable host address 130.56.255.193
  • last usable host address 130.56.255.254
  • broadcast address 130.56.255.255

For detailed calculation in binary you can refer to this answer

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