Migration from Microsoft Exchange 2003 to Microsoft Exchange 2010

What is the recommended steps to follow in a migration based on the following scenario?

Scenario
My client has a single Exchange 2003 Server hosting mailboxes for approximately 800 users.

Requirements
They would like to move to a multiple Exchange Server environment but want the new servers to be Exchange 2010 and have a need to retain the existing Exchange 2003 server for the moment.

There must be no disruption to OWA during this migration.


ECTechSupportAsked:
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Maen Abu-TabanjehNetwork Administrator, Network ConsultantCommented:
am still thinking about your question actually without interruption or 0 time its almost impossible but decrease interruption is possible ..
read this

http://technet.microsoft.com/en-us/library/dd638130.aspx
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Bruno PACIIT ConsultantCommented:
Hi,

If you accept that a user can not access his mailbox during the move of it to the new Exchange 2010 environment then YES you can migrate with no service interruption.
The mailbox move is the only period of time where users won't be able to access their mailbox,but if your Outlook clients are configured with cached mode then this interruption is well accepted by users as soon as they have been informed. During the move they can still access their local copy of their mailbox and will obtain a popup at the end of the move saying that they need to relaunch Outlook.

About OWA, when you have installed the new Exchange 2010 environment, and before you start to move maiboxes, you make things so that both OWA pages (the 2003 one and the new one) are published to external users. The new one should be the one that users access at first using the usual URL. The old one (the OWA 2003 page) is published under a temporary URL. You'll have to change certificates during this phase because of the temporary URL that shoudl match with the certificate name of the OWA 2003 page.
You indicate the "legacy" URL for OWA 2003 on Exchange 2010 so that it can redirect OWA clients to the legacy OWA 2003 page if the user that connects still have his mailbox on exchange 2003.

Have a good day.
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ECTechSupportAuthor Commented:
Does the fact that there is no Exchange 2003 F/E Server in the environment come into play?
The intention behind this is also to de-centralize the Exchange environment with the long term plan being to only host Exchange 2010 servers.
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Bruno PACIIT ConsultantCommented:
Hi again,

As soon as your current Exchange 2003 environment is working and OWA 2003 is working there is nothing to do with the details of the Exchange 2003 architecture.
Exchange 2010 install side-by-side with Exchange 2003 but do not require specific Exchange 2003 design. You only have to upgrade to Exchange 2003 SP2 if you don't have done it yet.

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ECTechSupportAuthor Commented:
Hi,

The Exchange 2010 server will be installed at a remote site that is not the entry point into the network. Mailboxes for users residing at the remote site will be moved to the Exchange 2010 server. It makes sense to host the OWA pages at the existing site doesn't it? Will I need a Exchange 2010 CAS before starting this implementation.
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Maen Abu-TabanjehNetwork Administrator, Network ConsultantCommented:
this article will be helpful when upgrade client access without interruption :

http://technet.microsoft.com/en-us/library/ee332348.aspx

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Bruno PACIIT ConsultantCommented:
Hi,

On Exchange 2010 the OWA pages are hosted by CAS servers. If you want to host OWA 2010 pages on the entry point site then you MUST install some CAS servers on this site ONLY for that !
You will need CAS servers on the site where the mailboxes resides because it a requirement of Exchange 2010.
That means that if you want to setup what you explained you will need CAS servers on the central site just for OWA !! I think this is not the good choice.

If you don't want to change the entry point for internet users you can use a reverse proxy product like TMG on this central site to publish CAS servers of the remote site. Doing like that you protect your CAS server from internet hackers usng TMG functionnality and you don't need CAS servers on the central site.
TMG is the ideal product to publish OWA pages 2003/2007/2010 and it will help you to give access to OWA pages 2003/2010 during the migration phase.

The classical steps to publish OWA during a migration phase are: (let's suppose your current OWA URL is webmail.domain.com)

1) publish the OWA 2003 page under a new  temporary public URL, let's say https://legacywebmail.domain.com/exchange
2) obtain a new SAN certificate from a public CA that match at least names "legacywbemail.domain.com" and "webmail.domain.com" (some other names are needed in the certificate if your plan to use ActiveSync external clients or OMA clients).
3) configure the Exchange 2010 CAS settings so that it redirects to https://legacywebmail.domain.com for not migrated mailboxes access.
4) publish the OWA 2010 page under the URL https://webmail.domain.com/owa.

If an external users access to the URL https://webmail.domain.com/owa he gets a credentials request coming from the TMG server.
The TMG server verify the credentials requesting DCs of the domain.
If the credentials are ok the TMG server sends the credentials to the Exchange 2010 CAS servers and ask for the OWA 2010 page.
The CAS server uses the credentials to locate the mailbox.
If the mailbox is on Exchange 2010 the CAS server give acces to the OWA 2010 page and the user can access his mailbox.
If the mailbox is on Exchange 2003 the CAS server provocate a HTML redirect to https://legacywebmail.domain.com/exchange.
The internet browser on the external client request for https://legacywbemail.domain.com/exchange and reach the TMG server again.
The TMG server see that credentials cookie is already known and valid and do not reask for credentials.
The TMG server sends credentials to the OWA 2003 server.
The OWA 2003 server uses credentials to locate the mailbox and give acces to it and the user can access its mailbox.

That's a resume of the steps. Of course it's not that simple and your need some TMG publishing knowledge and certificate knowledge. But it's the schema.

TMG will reach the OWA pages where they are, even if they are on a remote site. So you don't need CAS servers on the central site if you don't have mailbox servers on this site.


Have a good day.
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ECTechSupportAuthor Commented:
Hi PaciB,

Many thanks for all your advice thus far. I have not done any Exchange 2003 migrations or transitions to Exchange 2010 yet but will definately test the process in a LAB before any attempt in a live enviroment.

From all the reading done in the past few days, can I ask if the following implementation plan will work?. I will just make mention of all the major steps for now but please feel free to correct or advise where necessary. I need to get a plan to the customer as soon as possible for budgeting purposes only at this stage.

Please note that Implementing TMG is not an option. Currently OWA is hosted directly from the existing Exchange 2003 server.

Existing Environment
Single Exchange 2003 Server

Implementation Plan
Step 1  -  Install an Exchange 2010 server in the current site with the CAS Role
Step 2  -  Install an Exchange 2010 Mailbox Server at the remote site with the Hub Transport Server  Role
Step 3  -  Move relevant mailboxes to the Exchange 2010 Server at the Remote SIte
Step 4  -  Co-exist for appromixately 3 months and then Install a second Exchange 2010 Server at the Exchange 2003 Site as a Mailbox Server and Hub Transport Server. Move all remaining mailboxes to this server.
Step 5  -   Decommission the Exchange 2003 Server
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ECTechSupportAuthor Commented:
None of the solutions completely answer my quiestion
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