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I have always used the subnet tools on the web when our datacenters provide us with new ip blocks for our machines. However, I recently ordered more IPs from our European DC and they apparently just hand you random single IPs instead of blocks, which has left me confused.

How can I get the subnet for these IPs?

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i'd suggest opening a ticket with your provider they can just tell you the subnet mask to use... its probably anyway – anthonysomerset Jul 21 '11 at 13:14
up vote 3 down vote accepted

You can not. You can get the possible smallest one but without knowing more information you can not deduce which subnet you have because the "subnet" may be LARGER than the Class network.

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Alright, thank you! – Brett Powell Jul 21 '11 at 12:14
What "Class" would that be? – John Gardeniers Jul 21 '11 at 13:26
The ones abandoned when CIDR was introdued that many still think of - like "class C network". – TomTom Jul 21 '11 at 13:30

If they're assigning you random IPs, one of two things should be the case:

1) You already have some routing scheme arranged with them, and they can route a simple /32 to you.

2) You already have an interface in a subnet that includes that IP address. They are basically just giving you permission to take that additional IP address as well as the ones you already have.

If neither of these two things are the case, ask for clarification.

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