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Exchange 2007 CAS Server

Posted on 2011-02-23
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Last Modified: 2012-06-21
Microsoft recommends to install CAS server, then HUB server and the Mailbox Server in the co-existence scenario.
what are the technical reasons behind this?
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Question by:ckeshav
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11 Comments
 
LVL 33

Expert Comment

by:Busbar
ID: 34958851
This is because CAS and service as interface for clients without a need for HUB. and Mailbox needs HUB and CAS in order to function.
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Author Comment

by:ckeshav
ID: 34958864
This will all come to picture once you are having the mailboxes in Exchange 2007. I understand HUB server is required for the Mail transport to happen between Exchange 2003 and 2007, so HUB is required before the Mailbox server. But there is no specific reason why CAS first.
We can install HUB and then CAS and then the Mailbox server...but why does Microsoft recommend to install CAS first...there should be some technical reason behind this?
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Accepted Solution

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Busbar earned 750 total points
ID: 34958872
as I said it is just a recommendation, you can do it as you said.
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Expert Comment

by:Amit
ID: 34958875
It depends what kind of env you are trying to setup. If it is CCR then HUB will come first then CAS and MB role.

Why Hub?

Because when you go to which ever cluster node, the install is going to tell you that a hub transport server is not found.

If you have doing all roles in one server, then everything will automatically be done by setup.
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Expert Comment

by:Amit
ID: 34958878
In any scenario HUB is first, then CAS, then MB
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Author Comment

by:ckeshav
ID: 34958914
I have seen HUB getting installed first in a Typical installation. I'm talking about custom installation.

See the content in the Microsoft Document. But even here they do not clearly say that why CAS first, they combine the discussion.

http://technet.microsoft.com/en-us/library/aa997610%28EXCHG.80%29.aspx
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If you want to deploy the server roles for your organization on more than one computer, and if you are installing Exchange 2007 into an existing Exchange 2003 or Exchange 2000 organization, we recommend that you deploy the server roles in this order:

   1. Client Access server role
   2. Hub Transport server role
   3. Mailbox server role
   4. Unified Messaging server role

You can deploy the Edge Transport server role at any time during the deployment phase. However, the Edge Transport server role will not be fully functional until you install the Hub Transport server role and subscribe the Edge Transport server.
An Exchange 2003 or Exchange 2000 front-end server cannot provide access to an Exchange 2007 Mailbox server. In addition, an Exchange 2007 Mailbox server cannot send or receive e-mail messages if a Hub Transport server does not also exist in its Active Directory site. Therefore, when upgrading an existing Exchange organization, we recommend that you install the Client Access and Hub Transport server roles before installing the Mailbox server role. If you install the Mailbox server first, you will not have client access or mail flow to or from the Mailbox server until you install the Client Access and Hub Transport server roles.
-------------------------------------------------------------------
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Expert Comment

by:Busbar
ID: 34958922
no the correct approach is CHUM so hub second, but again this is just recommendations.
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Expert Comment

by:Amit
ID: 34958932
You try this in CCR. Then post the results
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LVL 8

Author Comment

by:ckeshav
ID: 34958965
Amit,   Busbar is trying to Say

CAS - HUB - Mailbox (recommended)

But

HUB- CAS - Mailbox will also work

I don't think so you will be installing any mailbox role CCR, LCR or just Mailbox w/o installing the 2 server roles. But I still did not get a clear answer why CAS is recommended by Microsoft first.

Some one asked me this in one of the job interviews and I never remember reading this anywhere. I'm scratching my head from yesterday if there is really any technical reason for this but w/o vain.

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LVL 45

Expert Comment

by:Amit
ID: 34960312
Hey Guys,

Appologize for any confusion. But if you read the article given by ckeshav. It says
"If you are installing Exchange 2007 into an existing Exchange 2003 or Exchange 2000 organization, we recommend that you deploy the server roles in this order:"

Client Access server role

Hub Transport server role

Mailbox server role

Unified Messaging server role

So the condition is mainly for coexist. Now next question Why?

Why CAS?
An Exchange 2003 or Exchange 2000 front-end server cannot provide access to an Exchange 2007 Mailbox server. That's why we need to put CAS first.

Why HUB Second?
Exchange 2007 Mailbox server cannot send or receive e-mail messages if a Hub Transport server does not also exist in its Active Directory site.

So next is HUB. Then we can proceed with MB role.

Apart from above condition. If we are doing typical or pure 2007 forest installation. We can do CAS>HUB>MB or HUB>CAS>MB. As without these three Exchange will not going to work.

I hope we all are clear now.



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Author Closing Comment

by:ckeshav
ID: 34989447
I did not get the complete technical answer I was looking for
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