Active Directory site redirection fails when accessing ECP from a remote site in Exchange Server 2016

Original KB number:  4056664

Symptoms

Consider the following scenarios:

• You have more than one Active Directory site.
• You configure the redirection for Exchange Control Panel (ECP) for those sites by adding the ExternalURL property for the /ECP virtual directories.

In this scenario, redirection fails when you try to access ECP from a remote site, and you receive the following error message:

Error 400: The length of the query string for this request exceeds the configured maxQueryStringLength value.

Cause

The virtual directory in the 302 response that's created by the Microsoft Exchange server on the local Active Directory site contains incorrect data. This causes the browser to enter a loop that eventually ends with the local Exchange Server issuing the Error 400 message.

Workaround

To work around this issue, remove the ExternalURL property from the ECP. Then, when a user accesses the ECP from the remote site, the user will be proxied to the ECP in the targeted Active Directory site. For more information, see Understanding Proxying and Redirection.

Status

Microsoft is working to resolve this problem and will post more information in this article when the information becomes available.