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Subnetting

Posted on 2001-09-17
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Last Modified: 2010-04-11
I work for a company that has 13 IP addresses. All of them are currently being used, and I have to add 2 printer servers to the network. I know I can do this through subnetting. The Subnet Mask is 255.255.255.240. Since I have to supply the printer servers with IP addresses as well, is there some way I can create a new subnet mask so I can have more IPs to use and still get he network to be accessible to the internet as well? I know I'm close here, but my text books aren't clear enough and my schooling was long enough ago without actually putting anything into practice that I find myself having to re-teach myself on the fly as situations arise.

Thanks in advnace,
Zac

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Question by:GilleyZ
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by:scraig84
ID: 6487652
Are these private or public addresses?  Since you are using that small of a subnet mask, and you have 13 addresses (I'm assuming the 14th is for the router), I would assume public.  If this is the case, you will need to either get more addresses from your ISP (and most likely readdress everything), or you can perform some type of address translation (NAT) - which will also require readdressing everything.  This would allow you to privately address your network and use as many IP's as you like.  However, you will need to get something to perform the NAT, such as your router, or possibly a Proxy server etc.

On the other hand if it is private already, you will be able to slide the mask most likely and gain more addresses.  Can you provide more info on what you are connected to (Internet, other offices, etc) and whether or not this is public addressing?
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by:GilleyZ
ID: 6487686
All of the addresses are public. The first one is the gateway, the other 13 are the actual IPs that we're using. I was wondering basically if there was someway I could use the subnet masking to perhaps expand things a little on the private level, so I could sneak these print servers in. Perhaps establishing a small workgroup of printers in the office and having my users access them that way?

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scraig84 earned 75 total points
ID: 6487725
Not using your existing address space you can't.  Subnetting allows you to segment or chop up a large group of addresses, which the ISP has already done, and given you a chunk.  You can't expand beyond that for a multitude of reasons.  One, this would most likely be using another company's addresses.  Two, the ISP won't be routing anything to you for those addresses.

You could theoretically move the subnet mask, allowing you to add more devices, as long as you knew that any new addresses gained would not work on the Internet.  However, it is first and foremost not a good idea.  Second, if for some reason you ever had to communicate with a real host using one of those addresses on the Internet, it wouldn't work.  Just not a good idea.

Like I said earlier, I would recommend looking into a NAT solution and privately address on the inside, or look at leasing a larger address space from the ISP.  The only other solution would be to add a hub and router, put the printers on that hub, give them private addresses, and route to the printers.  Again anything on that hub would not be able to talk to the Internet, but you wouldn't have the other issues.  However, this is more of a patch fix in my mind, and I would still look into one of the other two solutions.
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by:GilleyZ
ID: 6487741
I will do that, thanks very much for your help.
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by:andyalder
ID: 6487786
I would agree with scraig84 that NAT or proxy would be the best solution, as they are public addresses there ought to be a firewall in place that can easily do this.

But as these are printers with no need of internet access you could also bind an additional private IP address range to the server and anything else that prints to them and put them on this alternate subnet.

Bear in mind that netbios only works with the first IP address bound to the card but other protocols (LPD probably in this case) will work with the additional address. So you cannot put a windows PC on the new subnet but you can move any printers and unix boxes to it to spare up an address or two.
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by:GilleyZ
ID: 6487836
I'm thinking that a firewall with a NAT would be the way to go, as I also need to find a firewall as well. Are there any good suggestions as to which firewalls offer the best of both worlds?
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