SBS2011 stuck on public IP

I have a 2003 server installed by some IT company over a decade ago, somehow they came up with this brilliant idea of using a public address for the internal network
I came across this server about 3 years ago, but by then, AD, DNS. ES are all already running, making matters worst, they also have Avaya IP phones and another bunch of IP related software installed.
I tried to fool the OS by changing the router IP back to a non-public IP, this allow the install stage through but then it can no longer find the old server name , kind of expected but I am desprate.
There are also around 40+ stations with a bunch of bespoke software that were installed on single user profile (not installed for All users).
I know I am asking for a miracle by the look of things, but is there anything I could try or a way to bypass the checks ?
Thanks as always.
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Hi Combemartin, where to start.
Try renewing the ip address on the Server, if the ip address has changed on the router and it nolonger sees the server,
disconnect from the router
on the server  go to your CMD prompt type in ipconfig space /release
ipconfig /release
plug in the router now
then type type in ipconfig /renew and reboot
the router should renew the ip address and see the server?
Sync them so to speak.
Reboot the router may also help.
Just first steps
CombemartinAuthor Commented:
Hi Merete,
Thank you for your post, I will try this in a few hours when I get to work.
One of my main concern is that even if I could sync and force the AD through, the fact that 2008 doesn't support public IP is a shadow on the installation, but I will give your suggestion a try first and see where it will take me.
Thank you.
Cris HannaSr IT Support EngineerCommented:
So are you trying to perform a migration?
Is the 2003 server SBS as well?
What is acting as the DHCP server, the router or the 2003 server?
Simplify Active Directory Administration

Administration of Active Directory does not have to be hard.  Too often what should be a simple task is made more difficult than it needs to be.The solution?  Hyena from SystemTools Software.  With ease-of-use as well as powerful importing and bulk updating capabilities.

CombemartinAuthor Commented:
I am hoping this to be a migration as I dont fancy rejoining 40+ stations as well as reinstalling their software on each machine.
The old server is a 2003 with Exchange 2003 (not SBS), and the new one is SBS2011
The router is DHCP.
Thank you.
Cris HannaSr IT Support EngineerCommented:
Well, there in lies the problem.  The Router does not also hand DNS information when it hands out IP Addresses.
I would install the DHCP server on the old Server 2003.   Start out with same range the router uses and turn off DHCP on the router.

Then you'll have to clean up DNS on the 2003 server.    Then you can change the IP range in the server 2003 DHCP server, change the Server 2003's static IP to match the new private IP range ....FYI...SBS 2011 really prefers the 192.168.X.X range.
So on 2003 I'd go with that.  Then when you've confirmed that Server 2003 is running again as expected, you should be able to do the migration.
Philip ElderTechnical Architect - HA/Compute/StorageCommented:
As Cris mentions the IP change is fairly simple. DHCP does belong on the DC not the router.

I have a blog post on changing the IP on SBS 2008 that is identical to the SBS 2011 process.

As long as the IP phones are DHCP they should flip over to the new subnet with no problems. The phone system PBX may have a static IP and so too may the printers/copiers/MFPs. Get a map of their MAC addresses and set up DHCP reservations for their IP addresses.

After flipping the subnet keep a laptop on the old subnet to log on to those devices and flip them over the DHCP to pick up their new IP address.

Phone systems are pretty flexible. The phones should pick up the PBX though contacting the phone vendor to find out may be a good idea.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
CombemartinAuthor Commented:
Hi, I managed to changed the IP and updated DNS, build a second server, joined and migrated FSMO across and all seem ok.
Thank you all for all your help.
That's great Combemartin well done!!
Thank you..
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Windows Server 2003

From novice to tech pro — start learning today.