Migrating OWA from 2003 to 2010 and Keeping the Same DNS Name with Minimal Service Downtime

Scenario

A company has recently had an Exchange 2010 Hub/CAS server and Exchange 2010 Mailbox Server implemented, and this is sitting alongside a pre-existing Exchange 2003 Frontend/Backend setup. The customer wants to keep their Exchange 2003 webmail address (owa.test.com in this example,) and the following post give a brief outline of a way to do this.

Preliminary Information Gathering

There is a public DNS A record for owa.test.com.

There is a 1 to 1 NAT on the external firewall which maps the public IP address for owa.test.com to the Exchange 2003 Frontend Server LAN IP address.

OWA is currently working for mailboxes on Exchange 2003, via the Exchange 2003 Frontend server on https://owa.test.com/exchange.

Walkthrough

Stage 1

Create a new public DNS A record for say owa2.test.com.

Create a new 1 to 1 NAT on the external firewall to map the public IP address for owa2.test.com to the Exchange 2010 Hub/CAS server's LAN IP address.

Configure the webmail on the Exchange 2010 Hub/CAS for owa2.test.com.

Test https://owa2.test.com/OWA works from the internet for an Exchange 2010 Mailbox.

Stage 2

Create a new public DNS A record for legacy.test.com.

Add an additional IP address to the Exchange 2003 Frontend server's NIC.

Create a new 1 to 1 NAT on the external firewall to map the public IP address for legacy.test.com to the Exchange 2003 Frontend server's secondary LAN IP address.

Test https://legacy.test.com/exchange works from the internet for an Exchange 2003 Mailbox.

Stage 3

Via the Exchange 2010 Management Shell, run the command> Get-OwaVirtualDirectory

[PS] C:\Windows\system32>Get-OwaVirtualDirectory

Name Server OwaVersion

---- ------ ----------

owa (Default Web Site) EXCH2010CAS Exchange2010

Via the Exchange 2010 Management Shell, run the command> Set-OwaVirtualDirectory EXCH2010CAS\OWA* -ExternalUrl https://owa2.test.com/OWA -Exchange2003

URL https://legacy.test.com/exchange

[PS] C:\Windows\system32>Set-OwaVirtualDirectory EXCH2010CAS\OWA* -ExternalUrl https://owa2.test.com/OWA -Exchange2003

URL https://legacy.test.com/exchange

Test https://owa2.test.com/OWA now works from the internet for an Exchange 2003 Mailbox.

Stage 4

Now simply arrange a time with the customer to flip the NAT and update the Exchange 2010 Hub/CAS so that any settings relating to owa2.test.com are changed to owa.test.com.

The NAT flip involves:

i. Remove the NAT for owa2.test.com.

ii. Point the NAT for owa.test.com to the Exchange 2010 Hub/CAS Server.

iii. Re-add the NAT for owa2.test.com to point to the Exchange 2003 Frontend server.

Test https://owa.test.com/OWA works from the internet for Exchange 2003 and Exchange 2010 Mailboxes.

The A record and NAT for  owa2.test.com can be removed if all is working satisfactorily.

When all mailboxes have been moved to Exchange 2010, then the A record and NAT for  legacy.test.com can be removed.

Caveat: This post only considers OWA and it is assumed that a wildcard SSL certificate is in place.

Credit: Thanks for this tip to the mighty Jotmaan Ghins