Exchange cross-site availability

Hello,

I have Exchange 2010 servers in two sites. Recently, users in Site A have been reporting that they can't see free/busy info for users in Site B. They get the hash lines with "The recipient's server could not be contacted" error. This doesn't happen every time and if you refresh the free/busy with ALT+K a few times, the free/busy will eventually populate. Users in Site B are having no trouble seeing free/busy for users in both sites.

Event ID 4002 appears on the CAS server in Site A, with the following text:

Process 3820: ProxyWebRequest CrossSite from S-1-5-21-4230717640-2408447126-919093004-1176 to https://SITEBCAS1.domain.local:443/ews/exchange.asmx failed. Caller SIDs: NetworkCredentials. The exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.ProxyWebRequestProcessingException: System.Net.WebException: The request failed with HTTP status 400: Bad Request.
   at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
   at System.Web.Services.Protocols.SoapHttpClientProtocol.EndInvoke(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.Proxy.Service.EndGetUserAvailability(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.FreeBusyApplication.EndProxyWebRequest(ProxyWebRequest proxyWebRequest, QueryList queryList, Service service, IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.ProxyWebRequest.EndInvoke(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.AsyncWebRequest.EndInvokeWithErrorHandling():<No response>. The request information is ProxyWebRequest type = CrossSite, url = https://SITEBCAS1.domain.local:443/ews/exchange.asmx
Mailbox list = <Joe User>SMTP:Joe_User@domain.com, Parameters: windowStart = 11/26/2014 2:00:00 PM, windowEnd = 12/26/2014 2:00:00 PM, MergedFBInterval = 30, RequestedView = Detailed
. ---> System.Net.WebException: The request failed with HTTP status 400: Bad Request.
   at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
   at System.Web.Services.Protocols.SoapHttpClientProtocol.EndInvoke(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.Proxy.Service.EndGetUserAvailability(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.FreeBusyApplication.EndProxyWebRequest(ProxyWebRequest proxyWebRequest, QueryList queryList, Service service, IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.ProxyWebRequest.EndInvoke(IAsyncResult asyncResult)
   at Microsoft.Exchange.InfoWorker.Common.Availability.AsyncWebRequest.EndInvokeWithErrorHandling()
   --- End of inner exception stack trace ---
. Name of the server where exception originated: SITEACAS1. Make sure that the Active Directory site/forest that contain the user's mailbox has at least one local Exchange 2010 server running the Availability service. Turn up logging for the Availability service and test basic network connectivity.

There are two CAS servers at each site. I'm seeing event ID 4002 on both of Site A's CAS servers and the URL for both of SITE B's CAS servers appears in the error. So, I can't narrow this down to a single CAS server. I have tried rebooting the CAS servers and that didn't help. There have been no recent changes and this has previously been working fine.

Thanks,
JJ
LVL 37
Jamie McKillopIT ManagerAsked:
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Jamie McKillopIT ManagerAuthor Commented:
We were able to figure this out. The cross-site proxy uses Kerberos authentication. We have WAN optimizers (Riverbed) that were interfering with the Kerberos authentication. Once we configured the WAN optimizers to not try to optimize the traffic between the CAS servers, the issue went away.

-JJ
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