Exchange 2007 & 2013 coexistence: should external IP for "" be different than for ""?

My customer has a single Exchange 2007 server, and wants to upgrade to a single Exchange 2013 server.  We will need both servers to coexist for a period of time, so that we can move mailboxes from 2007 to 2013 in a careful, controlled way.

According to the Exchange Server Deployment Assistant tool, we need to register a unique A record for the old server with our public DNS provider.  The Assistant suggests using "", for example.  Our regular record is, which we will point to the external IP of the Exchange 2013 server.  Here is the Assistant's exact text:

You need to create a legacy domain name system (DNS) host name so your legacy Exchange 2007 environment and Exchange 2013 can coexist. For example, if your domain name is currently, you're likely using a host name of or for external client access to Exchange. During coexistence, we recommend creating and using, for example, a host name of You'll associate the legacy host name with your existing Exchange 2007 server and associate your current host name (for example, with your Exchange 2013 Client Access server. Your end users will not see or use the legacy host name. It will be used by Autodiscover and Client Access servers when redirecting legacy users to a legacy server.

Client connections, including Exchange ActiveSync, Outlook Web App, POP3, and IMAP4, will be proxied or redirected depending on the protocol being used. After the legacy host name has been configured, users will be able to access their mailbox regardless of whether it's on Exchange 2007 or Exchange 2013. If you're upgrading from Exchange 2007 to Exchange 2013, the following will happen:

--ActiveSync and Outlook Anywhere connections will be proxied from Exchange 2013 to Exchange 2007.
--Outlook Web App connections be redirected from Exchange 2013 to Exchange 2007.
--Exchange Web Service (EWS) connections rely on Autodiscover to provide the correct URL to the client.

So, we need to tell our public DNS provider to create an A record for    I have a few questions about this:

1)  Should the legacy record point to the same external IP as the regular record, or a new one?  In other words, if points to, should also point to

I would guess that it should point to the same IP, so that 2013 can proxy/redirect connection attempts to the 2007, like the Assistant says.

2)  If the answer to #1 is no, and needs to have its own IP, on the router that will accept external connections for, do I need to forward any ports, like 25, 80, etc.  Do I forward them to the 2007 server, or the 2013 server?
Thank you!
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Jeremy WeisingerSenior Network Consultant / EngineerCommented:
They should be different IP addresses. For the legacy IP, you should forward port 443 and 80 to the 2007 server.

You may want to bring in a consultant to make sure the coexistence gets setup properly.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Naushad shaikhIT Consultant - Messaging SupportCommented:
It seem you are going to use Exchange2007 URL with with new exchange Exchange 2013

Let now think  your current exchange URL is with exchange 2007 now we are going to use same with Exchange 2013

For that create Legacy A record in local DNS point to Exchange 2013

Next-> change all exchange 2007 URL with and Exchange 2013 with

Change Autodiscover URL

above will fix Internal and external request too.

Now your exchange2013 CAS is internet facing  with same Public IP and SAN certificate .

whenever any external or internal user will try to access Exchange CAS 2013 will response  and once user type his credential   after it will get route to exchange 2007 or 2013 mailbox server depend open where his mailbox reside.
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.