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how to murge two business network that have the same Subnet.

Posted on 2010-09-13
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Last Modified: 2012-05-10
Our business recently murge with another one. We also need to murge both network with a VPN for the moment. My issue is that both network have the same subnet (10.0.0.0 /24).

On the branch office I have a Windows 2008 domain controller. I have multiple GPO, dns server, Active directory, ect...

I don't think that I can change the IP address of this DC like this. I want to know what should I do to prevent all possible trouble.

thank you.
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Question by:tblinc
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Expert Comment

by:bluepig
ID: 33661912
Your description needs more detail; however, let's try to answer. I am guessing that you have two physical locations, and that you need a VPN between them. I am also guessing that some of the IP addresses in location A are identical to some IP addresses in location B (eg both locations have a device with the address 10.0.0.1).
If this is the case, you cannot make a VPN between the two locations. You will have to renumber one of the locations first. (You are going to have to renumber one of the locations sooner or later; you might as well do it now)
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rfc1180 earned 250 total points
ID: 33662423
> My issue is that both network have the same subnet (10.0.0.0 /24).
This is fine and very typical; The idea is to eventually renumber, but you can use NAT to "hide" the networks until you get a Plan Of Action in place and time to renumber the numbers:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a0080093f30.shtml

Billy
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Author Comment

by:tblinc
ID: 33662699
Excuse me, currently both network have the same subnet address. I'll change site B subnet to 10.0.1.0 /24.

Like this, I'll be able to successfully build my VPN tunnel.

My question is the following. At site B, I have a windows 2008 Domain controller. I need to have some advise to change it's IP address in the new subnet.

I'm not sure that we can change the Domain controller IP address as a simple workstation since it have every dns entry and multiple gpo on it, wsus and thing like this.

Could you tell me which step I should use to change my DC IP address ?

Thank you and I hope that this is easier to understand.

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Author Comment

by:tblinc
ID: 33662801
rfc1180

This is actually not in place so I have time. Right now, this is what I want to do.. the Plan Of Action.
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by:rfc1180
ID: 33662962
unfortunately, I can not give you any advice on merging/changing the IP address of a domain controller as that is not my forte. I can, however, give you advice on VPN, NAT, and overlapping networks and have already explained that you can have overlapping networks with utilizing NAT on both endpoints of the VPN tunnel. This can get a bit ugly and tedious to manage but very very possibly as a migration strategy.

Billy
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Assisted Solution

by:TSGITDept
TSGITDept earned 250 total points
ID: 33665907
You can change the IP address of a domain controller.  It may complain a bit for a minute or two but I just did this with 4 domain controllers in January.  We moved to a new subjet and to a new building.

You will just have to check a few things:
-If there are any other DCs on the same subnet those will need to obviously be re-IPd to the new subnet for them to continue to communicate with eachother unless you have them bounce off of a local LAN router.
-If the DCs are serving DHCP you'll need to create a new scope for the new subnet as those new computers move into the new subnet.
-DNS may need some updating.  If you have, say, static reservations for anything and it moves to a new subnet you'll need to manually edit the static reservation.

Another option is to multi-home a server that's moving to a new subnet.  Ideally if it has more than one NIC you can put them on different subnets.  Just make sure you don't enter a default Gateway on both NICs.  Windows has problems if it has more than one gateway.
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by:TSGITDept
ID: 33665923
Multi-homing Update:  And when you've tested everything you can retire the old subnet.  Multi-homing gives you a more gradual migration option to simply moving a server to a new subnet.  For your purposes if you wanted to try it, it would likely only be as a migration tool.
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Author Closing Comment

by:tblinc
ID: 33834264
thanks
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