We are migrating from Exchange 2007 to Exchange 2013. We plan on having 4 servers with all roles on each of the servers.

Exchange 2013 Installation Tasks

a) Install the 1st exchange 2013 CAS & MBX role on the 1st server.
b) Install the SSL UC certificate
c) Use Split DNS methodology to avoid using the server names in the certifcates.
d) point all DNS to the new server
e) create a firewall rule to nat all mail.domain.com to this new server IP
f) configure all the internal and external urls on this server
g) setup the IIS same as the exchange 2007 server

Kindly add to the above if there are any post installation tasks to the above

Now my questions are

1. Do I need to move the OAB from exchange 2007 to exchange 2013
2. Do I need to perform all of the above tasks on the 2nd 3rd and 4th exchange 2013 servers

3. What must be the DNS entries for the 2nd 3rd & 4th exchange servers?

There are lot of things which depends on the configuration you are looking for for e.g.
Do you plan to have DAG?
Do you plan to have H/W load balancer of E2013 cas client connectivity?
Do you have reverse proxy?
Do you host your autodiscovery?

Once you have this answers probably there would be a clear picture on how you can plan ahead on it.

Apart from that one of your question 

Do I need to move the OAB from exchange 2007 to exchange 2013
You cannot move OAB you have to create a new Arbitration mailbox on 2013 and create a new OAB and map it a 2013 exchange server. and assign it to your 2013 MBX DB

Hi Sphilip,

Hope you are following the Exchange Server Deployment Assistant Guide for the setup. It should answer most of the questions.

1) No, you don't need to move the OAB, but mailboxes needs to be assigned explicit OAB prior to installation of first Ex2013, due to some architectural changes(read below).

2) I don't see much on Exserver side settings here, however you need to do all those present, don't configure anything directly on IIS, you need to use EAC or EMS only(including certificates)

3) DNS Entries could be single namespace (mail.contoso.com from Ex2007 url) if you want loadbalancing or can be separate based on separate sites.

You need to create a public DNS record for the legacy.contoso.com host name to point to the external IP address of your Exchange 2007 server.

You also need to configure the ExternalURL properties of your Exchange 2007 Outlook Web App and EWS virtual directories to use the new legacy URL.

Ex2007 nolonger uses the original namespace. Ex2013 redirects everything to ex2007.

You need to configure the autodiscover.contoso.com as well to point to Ex2013

Reference:

Before you install Exchange 2013, you need to make sure that all of the existing Exchange mailboxes in your organization are assigned a default offline address book (OAB). If you don't do this, any mailbox that isn't assigned a default OAB when Exchange 2013 is installed will automatically download the new OAB generated by Exchange 2013. If you have hundreds or thousands of mailboxes, this could cause significant network traffic and server load.

Roadmap 3: Exchange 2007 On-Premise to Exchange 2013 On-Premise

http://blogs.technet.com/b/mspfe/archive/2013/10/21/upgrading-to-on-premises-exchange-server-2013.aspx

I hope, the above given suggestions would be good enough to understand your concern in depth and proceed further into right direction.

However, I would like to refer you on this informative technet resource that covers almost all the required steps in order to accomplish this job in a flawless manner : http://blogs.technet.com/b/meamcs/archive/2013/07/25/part-1-step-by-step-exchange-2007-to-2013-migration.aspx

Moreover, while need to migrate users mailboxes from Exchange 2007 to 2013, you may also consider on this automated tool (http://www.exchangemailboxmigration.com/) that seems to be a good alternative approach to get this task done without having downtime or any further interruption.

Hi,

The above article talks about 1 Exchange Server. My scenario is having 4 servers with all roles on each of the server. Hardware NLB will be incorporated at a later stage.

Do I need to setup all 4 servers at the same time? or can I setup one, install certificates put the urls and add the dns etc and once everthing is up and running, can i incorporate the 2nd 3rd and 4th?

After which I can setup the DAGs?

If so, i like to know on how to setup the certificates,virtual directories and DNS for the 2nd 3rd and 4th?

A small scenario which you can try to use in your enviroment wherever applicable. Where None of your Exchange servers are going to accept external connection directly, You have reverse proxy which will accept the internet connection and send it to one of your CAS IP.
Create internal DNS A record E2k13CAS.local.domain.com and point it ip of your Exchange 2013 servers.

Install your first server (CAS/MBX) create a cert request where add E2K13cas.local.domain.com in the SAN from your internal Cert auth server.

Assign it on the server 
Change Virtual directory settings. OWA/ECP/Activesync/OAB and point it to https://E2K13cas.local.domain.com/ accordingly.

Change Auto-discover uri on the server use set-clientaccessserver command Accordingly if you already have published it on internet.
create a test mailbox on 2013 server test owa /outlook functionality.

Once that is successfully create 3 more DNS entry with same name and point it to ip address of other server and start install / cert config/ virtual direcrotry settings/ testing.

Please note this is just a high level steps as you progress there are micro steps which you have to perform when you proceed ahead.

Hi,

The above article talks about 1 Exchange Server. My scenario is having 4 servers with all roles on each of the server. Hardware NLB will be incorporated at a later stage.

Do I need to setup all 4 servers at the same time? or can I setup one, install certificates put the urls and add the dns etc and once everthing is up and running, can i incorporate the 2nd 3rd and 4th?

After which I can setup the DAGs?

If so, i like to know on how to setup the certificates,virtual directories and DNS for the 2nd 3rd and 4th?

No, you don't need to setup all the servers at a time. Install the first configure certs, DNS etc. Once you are happy with the setup, install the 2nd at your own leisure.

Configure DAG with two servers, test it again once satisfied, add another server to the DAG.

Its very much flexible, similar to adding\removing a server to a LoadBalancer.

Regarding the certificate, generate the first one from EAC or EMS and once you have the Certificate ready with the Private key use it over all CAS and HLB as you proceed with the install.

Hi,

Great advice from Satyajit.

As additional, here's an blog about Step-by-Step Exchange 2007 to 2013 Migration:
http://blogs.technet.com/b/meamcs/archive/2013/07/25/part-2-step-by-step-exchange-2007-to-2013-migration.aspx

Thanks