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Add additional IP network

Posted on 2008-09-29
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Last Modified: 2010-04-02
I have a 10.1.1.0 network, i have the need to have another such as 10.1.2.0, can I simply change my subnet mask from 255.255.255.0 to 255.255.0.0 and the two networks will talk?

Also where all do i have to change the subnet mask?  router, firewall, swithes, dhcp server?
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Question by:jrri
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by:tigermatt
ID: 22599016
Yes. A bitmask of 255.255.0.0 will be more than ample to get those two networks to talk.

The subnet mask needs to be changed everywhere. Anything which has a static IP address needs the bitmask changing, and you can then update it in the DHCP Server scope so that dynamically assigned clients pull the new bitmask through DHCP automatically.

-tigermatt
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by:jrri
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Are there any issues that may bite me or is it prett clean?

Mike
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tigermatt earned 350 total points
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The only potential issues are the actual switch over stage from the old bitmask to the new bitmask. Your servers will obviously need a restart before they will re-register and communicate with each other again.

You do have an alternative. You can keep both networks with a subnet of 255.255.255.0, but configure the router with a different subnet. This technique is known as Variable Length Subnet Masking (VLSM) and it is quite common on larger networks. I am using it here at home right at this point in time.

Essentially you keep both subnets as 255.255.255.0 as I already said, but set the router to something like 255.255.0.0 as the bitmask. This means the router can then communicate across both the networks. The only difference is any traffic destined for the 10.1.2.0 network would need to pass through the router, but I consider this a minor inconvenience compared with doing a bitmask change across your whole site.

Each subnet will appear as a different subnet in its entirety. Netbios Browsing, for example, will not work, because it is restricted to a specified subnet. That is the only other downside I can think of to this approach.

-tigermatt
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