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i'm having trouble creating a IP Adressing Scheme, I have been given 15 sites each of these are connection via MPLS or leased line. For the first site I have determined I need 1700 nodes my tutor also said it requires 50 WAN links and 70 subnets (But I don't understand the reason for this)

I have got an IP address of /21 and a mask of

Am I right in thinking that leaves me 21 bits left, making it a /21 network with a max of 2046 hosts?

I'm using a Class B network but am not quite sure if that is big enough, if not I would change it to Class A ?

The problem am having is how can I calculate the IP scheme and how many hosts I can have one each one?

Thanks for any advice.

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Have a look here it may help – Iain Nov 28 '10 at 18:53
up vote 1 down vote accepted

Whilst this does sound like homework (you mentioned your tutor.. dead giveaway) .. Read How does Subnetting Work? and then it should be a bit easier.. That's a really good explanation imho.

Right. The second point. Nobody uses classfull networks any more. You're talking about a Class B network.. That doesn't really exist any more.. Everything is referred to by its netblock size, so Class C is /24, Class B is /16, Class A is /8.

Also, remember that the usable hosts on any network is -2 of the size of the available network, ie, you need one address as the network address, usually the .0 address, ie in ("a class C network"), then your network address is .0, and you need broadcast too, which is, in this case,, and then you have 253 usable hosts, (.1 to .254)

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"Nobody uses classfull networks any more."??? A lot of people make this statement but if you assign a static ip address to a Windows machine it sure looks like Microsoft is using the old classful rules to determine a mask. I agree that it is better to use the prefix, but is anyone confused about what the prefix is when you say Class X? – dbasnett Dec 5 '10 at 15:17
That's because Microsoft are still behind the times. ;) – Tom O'Connor Dec 5 '10 at 15:48

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