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Changing Network IP Addresses

Posted on 2013-01-10
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Last Modified: 2013-01-11
I will soon be implementing a Firewall in my network.  Currently I have 2 separate networks, both are all static IP (internal), each network has their own external IP and Router.  With the new Firewall, I will eliminate the two routers and separate the networks through IP Subnetting.  Both networks currently have an internal IP convention of 192.168.1.xxx.  In order for the Firewall to separate the networks properly, one of the networks will need to change to 192.168.2.xxx.  This is the network I have questions about.

I have a server running Windows Server 2008 R2 Standard.  My biggest concern is to make sure the DNS is properly changed from 1.xxx to 2.xxx.  Changing the IP's on all the clients and printers should be easy enough.  I also have a Netgear GS748Tv4 Switch that also has an IP address that will need to be changed.

I will be changing the network over on the router first so that (hopefully) the Firewall will be just a plug and play install (since it is already pre-programmed).

Is there some sort of procedure to properly change the IP address of the DNS?  Would I need to use the command [ipconfig /flushdns] on the server?  On all the clients?  I just don't want to miss anything and have my network crash when everybody is in it the next day (approx. 40 endpoints).  

Also, in what order should I change the IP's?  (i.e. Router 1st, Server 2nd, Switch 3rd, etc.)

Thank you in advance.
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Question by:lordzack
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by:atechnicnate
ID: 38763583
Are you planning on adding a second IP to the DNS server so that it will exist on both .1.x and .2.x or adding a second server?  

If the IP of the switch is simply for management and it's otherwise a layer 3 switch then I would start with one client and change it to a .2.x address and then setup the server to have a dns record for that client.  Next, flush the dns on the client and do a "nslookup newdns.record.toclient" (also on the client) to make sure it resolves properly.  That should prove DNS for the .2.x range and your alternate IP addressing scheme.  

Assuming that the switch IP is just management do you really need to change the IP on it or just leave it on the .1.x network?
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by:lordzack
ID: 38763752
The current server will change from .1.x to .2.x.  When completed, it will no longer accept any .1.x IP's after the change.  So to answer your question - I will be replacing not adding. I will also need to change the IP on the switch.  I am a little unclear (and uneducated) on the functions of nslookup and how to effectively use that command.  Could you be very specific on how to use that command and what information I am looking for?
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by:atechnicnate
atechnicnate earned 250 total points
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First I would create a record for a client ip.  For example, 192.168.2.101.  Then, create an A record and a reverse lookup record on the server and give 192.168.2.101 for the IP.

Next, I would change the server IP, then change the switch IP, then change one client.  Finally, on the client, change it's dns server to be the new IP of the DNS server.  Then open a command prompt as admin and run:

ipconfig /flushdns

then:

nslookup 192.168.2.101

It should return something like:

C:\Users\user>nslookup 192.168.2.101
Server:  mydns.server.name.com
Address:  192.168.2.1  <----- IP of DNS Server

Name:    client1 <-----------  Record you created for this client
Address:  192.168.2.101


That will show that it queried the proper DNS server for the client IP and returned the name you assigned it.  From there, just change the other clients over and modify DNS records to match.
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DrDave242 earned 250 total points
ID: 38764015
Is there some sort of procedure to properly change the IP address of the DNS?  Would I need to use the command [ipconfig /flushdns] on the server?  On all the clients?
Change the IP address in the server's NIC properties as you would on any other machine (and change its DNS server as well, of course).  Then check the server's properties in the DNS console and make sure it's listening on that address.  (I think this changes automatically when you change the server's address, but I don't recall for sure.)  Create a reverse lookup zone for the new subnet, if desired.  Run ipconfig /flushdns and ipconfig /registerdns on the server to make sure its host and PTR records are registered properly.  If the DNS server is also a domain controller, it wouldn't hurt to restart its Net Logon service as well.

The resolver cache on the clients may get flushed automatically when their IP addresses are changed, but it couldn't hurt to run ipconfig /flushdns and ipconfig /registerdns on them as well after you've changed their addresses.

Also, in what order should I change the IP's?  (i.e. Router 1st, Server 2nd, Switch 3rd, etc.)
Router first, definitely.  Then the server, the clients, and finally the switch, since that's most likely just a management IP address.
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Author Comment

by:lordzack
ID: 38767067
I have tested the changeover on another system (sbs2003) and everything works fine if I delete the Forward Lookup zone (mydomain.local) and then add it back under the same name.  It repopulates the client A records. Is this the best way? Or should I not delete it and do something different?
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by:atechnicnate
ID: 38767198
To be honest I'm not certain why that would be required.  However, if removing and re-adding that auto repopulates the A records then I'd go with it.
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by:lordzack
ID: 38767300
I have changed the IP address of the server/router/DNS without deleting/adding the Forward Lookup Zone and the records did not change their IP address, not even for the server.  AND everything works OK but I feel like I'm missing something.  Can you tell me what the ramifications would be if either I deleted/added a new record or did nothing?
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by:atechnicnate
ID: 38767688
If I understand correctly what you are saying the DNS server still has A records for the old IP's correct?  If that's the case then internal DNS won't work because you'd type in something like client1.domain.com and it would resolve to 192.168.1.4 but the client would be at 192.168.2.4 so essentially internal DNS would be broken.  Will it let you just modify the existing record to update it to the 192.168.2 subnet?
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