Exchange 2013 co-existence with Exchange 2010 proxying issue.

Question

Hello,  
I am testing Exchange 2010 and Exchange 2013 co-existence in my test lab at the moment, with
a view to migrating our production environment to 2013 later in the year.  
The lab is setup, and the problem I'm having is that internal Outlook clients cannot open
their respective mailboxes once the 2013 CAS server is introduced into the mix.  
 The
setup is listed below:  
EXCHANGE 2010 Servers  
TESTLABEXCH01 - CAS,HT,MBX - Exchange 2010 SP3  
TESTLABEXCH02 - CAS,HT,MBX - Exchange 2010 SP3  
Both servers are part of a CAS Array - casarray01.testlab.local  
Both servers are part of a DAG - DAG01.testlab.local  
RpcClientAccessServer on all 2010 databases set to casarray01.testlab.local  
The A record for casarray01.testlab.local points to the IP of the VIP of a load balancer.  
The loadbalancer serves
the following ports: 25,80,443,143,993,110,995,135,60200,60201  
OutlookAnywhere is enabled on both servers:  
ClientAuthenticationMethod : Ntlm  
IISAuthenticationMethods   : {Basic, Ntlm}  
Internal and external mail flow works without issue before the 2013 server is introduced. 
Internal and external client access works without issue before the 2013 server is introduced. 
Part Two to follow.....
Matt

Answer 1

EXCHANGE 2013 Servers :
TESTLABEXCH03 - CAS,MBX - Exchange 2013 SP1  
OutlookAnywhere is enabled on the server:  
ClientAuthenticationMethod : Ntlm  
IISAuthenticationMethods   : {Basic, Ntlm}  
RpcClientAccessServer on all 2013 databases set to casarray01.testlab.local
(This an inherited setting I assume from the pre-existing 2010 organization)  
Split DNS is in place and all internal/external URL's point to either:  
autidiscover.external.com  
mail.external.com  
The A record for the mail.external.com points to the IP of the load balancer VIP  
The CNAME record for autodiscover.external.com points to mail.external.com  
When the TESTLABEXCH03 is added to the load balancer config,
and given highest priority this is when the Outlook clients stop working.  
Any existing profiles in Outlook 2010/Outlook 2013 can no be opened as there is a persistent
credentials prompt.  
Upon trying to create a new profile, the process errors when reaching the "Log onto server"
stage and again prompts for credentials.  
Running the test-outlookconnectivity cmdlet from
either of the 2010 servers produces the following results.  
[PS] C:\Windows\system32>Test-OutlookConnectivity -Protocol:http  
ClientAccessServer   ServiceEndpoint                         
Scenario                            Result  Latency  
TESTLABEXCH02  autodiscover.external.com    Autodiscover:
Web service request.  Success  343.20  
TESTLABEXCH02  casarray01.testlab.local       RpcProxy::VerifyRpcProxy.  
Success    0.00  
TESTLABEXCH02  casarray01.testlab.local         RFRI::GetReferral.                 
Failure   -1.00  
TESTLABEXCH02  casarray01.testlab.local        NSPI::GetProfileDetails.           
Failure   -1.00  
TESTLABEXCH02  casarray01.testlab.local        
Mailbox::Connect.                   Failure   -1.00 
TESTLABEXCH02  casarray01.testlab.local        
Mailbox::Logon.                     Skipped   -1.00  
If remove the 2013 CAS server from the loadbalancer config and
all connections go directly to the 2010 servers again, all of the above tests pass and Outlook connectivity is also restored.  
IIS has been reset on all 3 servers incidentally, following any changes made whilst troubleshooting. 
I'm struggling to see what I'm missing here, if anyone can assist in troubleshooting this
matter further, or point out any errors in my setup it would be greatly appreciated.  
Regards  
Matt 
Matt