# Different subnet masks - same network



## phb5000 (Dec 23, 2007)

Hi,

For many years now my home network has consisted of 5 pcs/laptops all running Windows XP SP2. I've never had any problems with file sharing in my network workgroup before.

However, recently I noticed that all computers havent been able to find each other on the network. After looking into it I noticed that it seems like my network has been "split up" into 2 groups.

PC1 and Laptop1 can find each other in My Network Places (255.255.255.0)

and

PC2, PC3, and Laptop2 can find each other in My Network Places (255.255.254.0)

In attempt to find a difference in connection settings I noticed that some of the computers have automatically been assigned different subnet masks (as shown above).

I tried doing some research on how to possibly change the automatically assigned subnet mask, assigned by the DNS. However, the only solutions I found were the settings that can be changed for the TCP/IP protocol for a network connection. However, I do not wish to change these settings as I want to keep the settings as "Obtain an IP address automatically".

Why are the computers (on the same modem, and same workgroup) retrieving different subnet masks?

Is it possible to JUST change the subnet mask, and not the other IP acquiring settings.


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## JohnWill (Oct 19, 2002)

Please supply the following info, *exact make and models* of the equipment please.

Make *and* model of the broadband modem.
Make *and* model of the router.
Connection type, wired or wireless (for each computer).
If wireless, encryption used, (none, WEP, WPA, or WPA2)
Make/model of your computer.
Version and patch level of Windows on all affected machines, i.e. XP-Home (or XP-Pro), SP2, Vista, etc.

The only way I see this happening is you have two routers if they're all obtaining their address automatically.

On one computer from each "group", I'd also like to see this:

*S*tart, *R*un, *CMD* to open a command prompt:

Type the following command:

*IPCONFIG /ALL*

Right click in the command window and choose *Select All*, then hit *Enter*.
Paste the results in a message here.

If you are on a machine with no network connection, use a floppy, USB disk, or a CD-RW disk to transfer a text file with the information to allow pasting it here.


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## phb5000 (Dec 23, 2007)

Broadband Modem: XAVi, X7002r
Router: none (my ISP offers 5 IP addresses)

Switch 1: D-Link, DES-1005D
Switch 2: Level One, FSW-0508TX

Windows XP: Service Pack 2 (on all computers)

Network Setup: 









IPCONFIG/ALL:


> ========================================================================================================
> Laptop #1
> ========================================================================================================
> Windows IP Configuration
> ...


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## JohnWill (Oct 19, 2002)

Well, you have answered your question. When you get multiple IP addresses from your ISP, there is no guarantee that they'll be in the same subnet. Obviously, you're finding out that is the case right now. 

This is also a very dangerous way to do file/print sharing, since you're exposing your network directly to the Internet.

My advice? Buy a broadband router.


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## DongleFree (Nov 3, 2007)

It seems something wrong, if ur ISP gives u 5 IPs and u are using this modem, so u should be able to have 5 computers with static IPS and in the same range of ip and subnet mask , how many ports in this modem, why u are using two switches , if you can buy router it might fix it to have a private network all shared without problem and safe and u can use the static Ip by ip maping or port forward ,


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## JohnWill (Oct 19, 2002)

It may seem wrong, but that's the way it works.


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## skinnywhiteboy (Jan 26, 2001)

Right now it looks like all your computer on your network are exposed to the Internet. Definately buy a router, and use the main static address that your ISP gave you. The only reason you would need more static address is if you wanted to run certain services on your network like a mail server, etc. With your current set up, I see no need for every machine to have it's own static address. This can be very dangerous if you don't have the proper hardware to support that type of configuration.


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## JohnWill (Oct 19, 2002)

I don't think the router message is getting through.


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