Exchange 2010 co-existence with Exchange 2003 using a separate OWA URL

OK, Exchange 2003 - 2010 migration gurus, here is one for you:
We are upgrading from Exchange 2003 to Exchange 2010. All Exchange 2003 and Active Directory pre-requisites are met. We are about to install Exchange 2010 CAS role first, and the Exchange 2010 mailbox/hub transport roles on a different VM. The current external Exchange 2003 OWA URL is We have a requirement to use a different OWA URL for Exchange 2010 CAS such as The requirement is that existing Exchange 2003 users are going to continue using without interruption, while new test mailboxes in Exchange 2010 and any pilot mailboxes migrated from Exchange 2003 to Exchange 2010 will use the new Exchange 2010 URL ( The idea is that during that time period, a new SSL VPN solution will be tested and validated for Exchange 2010 remote access. Once the solution is tested and validated, the existing Exchange 2003 OWA URL will be switched to point to the Exchange 2010 CAS via the SSL VPN solution, and we will then create a Legacy DNS record to point to the Exchange 2003 front end server to allow for re-direction for users still on Exchange 2003. The questions are:
- Is this a valid approach?
- Will the introduction of Exchange 2010 in this manner not interrupt the user community during the co-existence period? Or will Exchange 2010 just take over?
Thank you
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You will require 2 public IP's for co-existence. One for Exchange 2003 and one for Exchange 2010.
You will have to purchase a certificate with which will include, and
install the certificate on both the exchange server.
Create the DNS a record in public dns.
Point to Exchange 2003 public IP and and to Exchange 2010 public IP.
Configure the virtual directories.
sfarhiAuthor Commented:
Thanks, R-R,
I think what you are describing is the normal default approach. What I would like to know is whether the approach I described above, which is different I believe, is valid and whether following that approach will cause any disruption to the users while we are testing/validating the SSL VPN solution for the temporary Exchange 2010 URL. We are planning to use a wildcard certificate by the way.
sfarhiAuthor Commented:
Just an update: I went ahead and followed the approach I described in my original question above, and was able to complete Exchange 2010 CAS deployment without any disruptions to users. I gave Exchange 2010 OWA a separate URL, and Exchange 2003 users are still getting to OWA with the original Exchange 2003 OWA URL, while Exchange 2010 users are using the new Exchange 2010 OWA UR internally. I also deployed HTS and Mailbox roles with no interruption to users. The external access solution (Juniper) is being tested and validated for the Exchange 2010 URL. The plan is that after that solution is validated, we will then change the Exchange 2010 external OWA URL DNS record to point to the external access solution IP address and change the Exchange 2003 OWA URL to point to "". We will also re-configure the 3rd party SMTP gateway we are using to deliver e-mail to Exchange 2010 and accept outbound e-mail from it instead of Exchange 2003.

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sfarhiAuthor Commented:
The information provided by the expert, while correct, is not completely relevant to the question. The input provided good common migration steps while the question was about a specific approach described in the original question.
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