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Exchange 2013/2010/2007 CAS URLs

CAS urls becomes very critical when you migrate from Exchange 2007 to Exchange 2013 and you are having 2 AD Sites with Exchange Server.

Now we are growing smarter and adapting new innovation like 3 datacenter expanded preferred architecture DAG (Kind of Geo Cluster), IP Less DAG (no CNO), Auto-reseed (Jbod and no raid), safetynet(more high available mails). Certainly we are heading to a great world. At the same time CAS connectivity planning is very crucial. So let us have a look on recommended CAS urls configuration.

When you have 2 internet facing sites then it is recommended to keep 2 different urls 1 per site so that Exchange can redirect the request to the 2nd AD site correctly. Keeping the same url will not work with Exchange 2007 because Exchange 2007 does not accept cross site redirection.

This is a site bound namespace

When we have single internet facing site then externalurl attribute in the non-internet facing site should be $null so that internet facing site can proxy to non-internet facing site.

This is a Unbound namespace


I have tried to summarize a great blog by Ross Smith IV –

Unbound Namespace

I was discussing unbound namespaces with Ross Smith IV and he explained that Exchange 2007 can only redirect to the local AD site so Exchange 2007 is out of question if we are planning unbound namespaces

In Exchange 2016 unbound Names Spaces will continue to work in the same way as Exchange 2013. This means Exchange 2010 and 2013 can use unbound name spaces in coexistence and 2 AD site infrastructure.

So if you have 2 AD site with Exchange 2016/2013/2010 then you can configure same External url for all.

From Exchange 2016 onwards, Microsoft is also recommending to use different internalurl than external url for Outlook anywhere and MAPI/HTTP to use different authentication mechanism in intranet (kerberos) than internet (NTLM or Basic). It is only useful if Internalurl is not resolving over public dns.

If we follow these guidelines then URLs will look like this.unbound urls

I hope this will help in clarifying more about the CAS URLs

Prabhat Nigam

Microsoft MVP | Exchange Server




4 Responses to “Exchange 2013/2010/2007 CAS URLs”

  1. Exchange Server 2016: All You Need to know Part 2 « Says:

    […] it is only useful when we have internalurl which in not available on Public DNS. I have explained namespace requirement here. […]

  2. DDog80sRock Says:

    In your last graph showing Exchange 2016/2013/2010 CAS URLs, why wouldn’t you use for all the internalURLs for the other virtual directories? Why continue to use the external URLs?

  3. Prabhat Says:

    you can do it. I recommend this so that you can reduce you SAN in the cert.

  4. DDog80sRock Says:

    Does that mean that you’re utilizing split DNS for the entry?

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