[ExchangeList] e2k7 CAS redundancy

Hi,
There is a requirement to provide redundancy for CAS server for a small 
organization. They are not ready to spend too much money , but want a decent 
redundancy.
 
Scenario is something like this:
Two location : A & B
In location A there is one CAS server and in location B there is another single 
CAS server. Mailbox servers are clustered.
Customer wants only one URL 
Also when CAS in location A goes down, users should be able to access it 
through CAS in location B. Customer do not want to invest in two CAS in one 
site just for this purpose. Currently they use exchange 2003 and it is meeting 
their requirement. Now they want the same thing with e2k7.
So now exchange 2007 sp1 on windows 2008 sp1 is setup. But it looks like I 
cannot use single URL with both the CAS site facing the internet, I need to 
disable external URL on one of the CAS site. Also if CAS in one of the sites 
goes down OWA will not work. How do I achieve this?
Am I missing something..i am stuck with this and finding it difficult to 
convince the customer. Can someone please help.
 
Regards
Praveen R

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