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Subnet mask question/problem

Posted on 2007-03-28
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Last Modified: 2013-11-13
Hi Experts:
I have a network that has two subnets.  Each subnet is at a different physical location and connected with a PTP T-1.  I have an SBS 2003 Server/Exchange Server at one location.  That subnet is 10.0.0.0.  I have a server 2003 machine at the other subnet and it is 192.168.10.0.  Each location has multiple workstations.  The network is functioning well and as expected with no known problems.  However, in preparing for some future changes, I just realized that most of the equipment (those with fixed IPs) like my firewall and VoIP server are using a 255.0.0.0 subnet mask.  But, my SBS server is using  255.255.0.0 subnet mask.  It has been this way for a long time.  My questions:
Is this a problem?  
Should I change the mask on the SBS machine to 255.0.0.0?  
If I do, will I have any potential network communication issues?  
For the routing table in my Adtran NetVanta 3205 connected to the 192.168.10.0 end of the T-1, should the subnet mask for 10.0.0.0 be 255.255.0.0 or 255.0.0.0 or will it make any difference?
Any related issues I should be aware of?
Please limit the "jargon" in your response if possible as I have no formal network training.  Plenty of seat of the pants experience and a logical mind that can figure out just about anything as long as all of the words used make sense.

Thanks in advance for the help.
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Question by:normsrv
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by:jaredcall
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At this point, technically, it's not a problem.  Procedurally, you should be consistent or else you're going to create problems for yourself later on.

Limiting the tech explanation as per your request:
  Standard mask for 10.x.x.x is 255.0.0.0.  255.255.255.0 is also common.
  Standard mask for 192.168.x.x is 255.255.255.0 .

-jared
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by:normsrv
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With the mixture of 255.255.0.0 and 255.0.0.0 should I be expecting a particular problem to show up?  Or, by changing the server to 255.0.0.0 should I be watching for a particular problem?
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by:COE-IT
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normsrv:

To answer your question - no, using different subnet masks on different networks is not a problem. For devices to communicate on the same network (subnet), they all must use the same subnet mask. If you wanted the VoIP server and your SBS server to be on the same network, they both must use the same subnet.

The important thing here is whether your servers and workstations can communicate, which it sounds like they can. They are able to communicate because your router knows how to route between the 10.0.0.0 and 192.168.10.x networks.

If you were to change your SBS server subnet mask to 255.255.0.0 (class B), that server would lose connectivity to the 10.0.0.0 network. So don't do that :)

The number of subnets and hosts you need on your network determines the ip addressing and subnet mask you use. If you are running out of IP addresses for subnets or hosts (which it doesn't sound like you are), then consider changing your IP scheme. Otherwise, I would leave everything the way it is.
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by:COE-IT
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Sorry, I meant:

"If you were to change your SBS server subnet mask to 255.0.0.0 (class A), that server would lose connectivity to the 10.0.0.0 network." :)
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by:normsrv
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Everything except the SBS server on the 10.0.0.0 subnet is on 255.0.0.0 except the server.  I was surprised when I found this because everything is working as it should and has for many months.  However, it just doesn't seem right.  I don't want to change it if there is no real reason for is.
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jaredcall earned 500 total points
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The only reason to change anything at this point is to avoid potential confusion later.  It should continue to function just fine as-is.
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