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Net Mask

Posted on 2011-04-19
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I know I'm going to feel like a moron when I hear the answer but...My sonicwall LAN interface is set up to 10.0.0.x / 255.0.0.0 but my machines are using 101.0.0.x with a netmask of 255.255.255.0...I didn't set this up , but it doesn't seem to make sense. Am I missing the logic behind this configuration? Also, if it is wrong, how do I change it? I'm not sure how the networked machines are picking up this netmask.
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Question by:jskiba
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Lee W, MVP earned 500 total points
ID: 35427099
101.0.0.x is a potentially public network and as such, if you ever needed to access a web site or send e-mail to someone who legitimately has that address, you would have serious problems.  10.x.x.x is a private address and anything starting with 10. can be safely used.

You change it by documenting your network, what has what address, and then change it to something that starts with 10.x.x.x.  If you have to other things depends on what's on your network.

(a mask of 255.255.255.0 means that all devices EXPECT the first 3 sets of numbers to be the same.  So to communicate properly, if you use 10.11.12.x, all your machines MUST start with 10.11.12.x.  You could, in theory, go with 10.11.x.x and a mask of 255.255.0.0 but in general, people don't do that.  Further, there are things called supernets that could be, for example 255.255.248.0 - but in my opinion, you want to stay clear of them as they can complicate things a little unnecessarily.  Basically, in every spot with a "0" YOU can set whatever number (1-254) you want so long as the entire address is unique on your network.
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by:jskiba
ID: 35427198
What a fast response! Thank you.
The internal netmask used to be 255.0.0.0 which made subnetting easier. This is how I found the issue. I want to set up a subnet separate from the LAN with internet access only. Of course, when I try to create an address pool of 10.0.2.x on subnet 255.255.225.0, my Cisco WLC gives me an IP misconfig error.

I'm wondering where I set the default internal netmask to 255.0.0.0

Of course, I admit I might be way off in my way of thinking. Maybe I can get a quick education here.
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by:Lee W, MVP
ID: 35427237
Can you explain how large your network is, why you need some on the internet, some off and in general, just be more detailed?  We don't necessarily need every tidbit, but I have no idea if your lan is for 10 people 10,000, if you use Windows systems or Linux or Mac or something else entirely, etc.
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by:jskiba
ID: 35427385
Sure
it's a small virtualized network with 5 servers and 50 clients. However, we have a wireless guest network that will occasionally need to support up to 150 connections during large events.

Windows 2008 server
DPM server on a Dell box
all windows clients

I realize I don't need all the addresses that a 255.0.0.0 mask would allow, but I don't want to reconfigure the DHCP pool for the entire network.

We have a second organization in the facility that leases from us and shares the T1. They are on a class C network (192.198.1.x) and I don't administer their network. So I think my predecessor might have set up our addressing to avoid conflict...but there's no way to tell.
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