cas coexitence

i having migration scenario in which i needed to coexist new cas server i.e. 2013 to 2010 ORG with minimum downtime because our 80% users connected to OWA every time.
ELS ELSAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
When you install Exchange 2013 in a coexistance environment with Exchange 2010 you will need to install the mailbox role first. After the mailbox role is installed you can then install the CAS role. When you install the CAS role you need to perform a series of steps before your Exchange 2013 will act as the Primary CAS server.

You need to do the following...
- configure virtual directories
- install certificates
- enable certificates
- configure NAT-ing on your Firewall for your public IP to point to the 2013 CAS server rather than the 2010

At this point you should not have any down time for Exchange. However, even if you do not have mailboxes moved over to the 2013 mailbox server clients that are on the 2010 Exchange server will be re-directed automatically to the Exchange 2010 CAS server.

I would highly suggest that you use the Exchange Deployment Assistant to help you through this process.

Exchange Deployment Assistant
https://technet.microsoft.com/en-us/office/dn756393.aspx

Will.
MASEE Solution Guide - Technical Dept HeadCommented:
As suggested by Will the below steps will avoid downtime.
- configure virtual directories
- install certificates (make sure you have the requied SAN names in it  i.e. mail.emaildomain.com and autodiscover.emaildomain.com)
- enable IIS and SMTP services on the new certificate.
- configure NAT-ing on your Firewall for your public IP to point to the 2013 CAS server rather than the 2010

Use this to create CSR command
http://gallery.technet.microsoft.com/Exchange-20072010-and-2013-17a0b52f
ELS ELSAuthor Commented:
can you tell me a simple reason why mailbox need to install first in case of 2013, in case of 2010/2007 we were installing cas first or it is for my case only?
Will SzymkowskiSenior Solution ArchitectCommented:
Exchange 2013 is a completely different architecture than 2007 or 2010. The Mailbox role does almost all of the routing now and having the mailbox role installed first is just a recommendation. CAS is the last thing that needs to be configured. However it is also recommended that Exchange roles CAS and Mailbox be installed on the same server to technically you could just install both roles during the installation and you will be fine.

As I also stated in my first post use the Exchange deployment assistant as it will guide you through the high level steps that are required.

This also deals with co-existing scenarios as well.

Will.

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ELS ELSAuthor Commented:
ok
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