By
default, Hub Transport servers are resilient. The Hub Transport role is
registered in Active Directory; therefore, as you add more servers with
the role, they are noted in the event of a failure. Load balancing
within the site is automatically configured with however many Hub
Transport servers you use.
The
only time this isn’t the case is when the HT role is installed on the
same server as the Mailbox role. This is logical because the Mailbox
server will automatically use the local HT server.
Sometimes
you might have a need to load balance your Hub Transport services. You
wouldn’t do this for most scenarios; however, you might have an
application that requires the relaying of messages. In the RTM version
of Exchange, you might have considered
a round-robin DNS or MX records, but with SP1, you have the capability
to use a hardware or Windows-based NLB solution.
Note
If
you do need to use Windows NLB for your Hub Transport servers, the
steps are pretty much the same as what we have for the CAS server to
enable NLB between your servers. However, remember that NLB is not
supported for load balancing your internal Hub Transport connections
(which are handled automatically). You would seek only to use this
solution on inbound SMTP connections from applications (perhaps a
Microsoft Office SharePoint Server or a System Center Operations
Manager solution) that submit messages to an Exchange organization
through an SMTP relay (because the applications cannot log directly
into a MAPI mailbox). These are unique scenarios, and we encourage you
to research thoroughly your solution before load balancing your Hub
Transport servers.
