Removing session affinity
As we saw in Chapter 1, Getting Started, Exchange 2013 does not require session affinity any longer. To understand why this is the case, let us look at how the new CAS role works from a protocol perspective:
A client resolves the namespace to a CAS.
The CAS authenticates the requests and queries Active Directory for the following pieces of information:
Mailbox version (if the mailbox is hosted on Exchange 2010 or 2013, for example; let us assume a 2013 mailbox)
Mailbox location information such as database and
ExternalURL
The CAS decides if it will redirect or proxy the request to another CAS or array (within the same AD forest).
The CAS queries the instance of the Active Manager responsible for the database in order to discover in which Mailbox server the active copy is hosted.
The CAS will either proxy the request to the Mailbox server currently hosting the active copy using HTTPS, IMAP, or POP, or, in the case of a telephony request, redirect it to the Mailbox server...
