Calculating Subnet Mask

[Tinus1959]

Originally Posted by JonGlory

You're right enough with the host Tinus, got mixed up with address there

Thank you. Never argue with a trainer.

But the original question is guessing a subnet mask

I.e network admin needs 256 networks with 256 addresses

Subnets ip 172.16.8.0 with 255.255.255.0

Well, I don't see the word 'guessing' there.
But maybe you are right. Lets have another look.

I have seen questions in the MSpress book that asks you to calculate the subnet from a given network or host address?? can someone advise me on how this is calculated

For example, say if I had a network destination of 172.16.8.0 - how do I calculate the mask?

Nope, no guessing. Simple question: How can I calculate the mask.

[JonGlory]

What I mean is to calculate the mask you would need to be Guessing/assuming that the network is subnetted a certain way.

Like you said in your original reply, it could be several masks.

The main point I'm making is, that the question that started this thread would never be asked in an exam with just that information alone, more would be needed to be able to calculate the answer, without that extra information you would have to give the answer as a best guess.

And that if you could determine an network and host portion of an IP address by just the network address only (where default mask are not being used), then there would be hardly any point in having a subnet mask.

[kevicho]

Originally Posted by Nimbus

Question about subnetting, I know the process of borrowing host bits from an octet to create subnets and how to calculate the subnet mask for the desired number of subnets.

I have seen questions in the MSpress book that asks you to calculate the subnet from a given network or host address?? can someone advise me on how this is calculated

For example, say if I had a network destination of 172.16.8.0 - how do I calculate the mask?

Thanks in Advance

Hey just some random musings here, working (on an assumption this is the first address on this subnet) out the grouping of the 3rd octet (ie from 172.168.0.0 to 172.168.7.255), that could give you 32 networks (ie 256/8 ) so to get 32 subnets, that is 2 to the power of 5 (which gives us 32) which means 5 network bits are used, which is 248, so the subnet mask could be 255.255.248.0

Also the hosts per network would be 2 to the power of 11 (as we have 11 host bits) which is 2048, take away the broadcast and the network address you 2046 per subnet (which is you time 256 by 8, number of networks, and remove the 2 addresses) you get the same answer)