+1 833 274 2566

What do you need load balancing for?

"We selected Loadbalancer.org for our virtualized Exchange 2010 cluster deployment a year ago. Since then the virtual load balancers have been performing flawlessly. Support is always very speedy in responding to questions. The sales staff has been very helpful as well. Overall we are very happy with our choice, and will gladly recommend them to other customers looking for a similar solution."

Kurt Tavares

City of Tracy

Load Balancing Microsoft Exchange

Microsoft Exchange Server, the mainstay of Microsoft’s Unified Communications solution has grown beyond being regarded as the standard in business email into a fully fledged communications tool.

Once difficult to manage at scale, the Microsoft Exchange platform has reached a level of maturity. With a simplified architecture, it has evolved to support high availability and scalability by design.

To implement highly available and scalable deployments of Microsoft Exchange Server, Microsoft recommends using a load balancer to distribute the traffic among multiple Exchange servers. Both current and legacy versions of Exchange support load balancing, with a different approach and recommendations dependent on the version you are running.

Example Exchange 2016 deployment using a minimal 2 server setup.

Exchange 2013 & 2016 Protocol Table

Protocol Role Ports Load balancing methods
TCP CAS 443 Used for Outlook on the Web, AutoDiscovery, Web Services, ActiveSync, Outlook Anywhere, Offline Address Book, Exchange Administration Center). Layer 4 DR (Direct Routing – Ultra-fast, local server based load balancing) Layer 7 SNAT
TCP CAS 25 Used for Inbound SMTP Layer 4 DR (Direct Routing – Ultra-fast, local server based load balancing) Layer 7 SNAT (Flexible, URL switching and cookie insertion capabilities)
TCP CAS 110, 995
143,993
Used for POP3 clients Used for IMAP4 clients Layer 4 DR (Direct Routing – Ultra-fast, local server based load balancing) Layer 7 SNAT (Flexible, URL switching and cookie insertion capabilities)

Exchange 2010 Protocol Table

Protocol Role Ports Load balancing methods
TCP CAS 80 Layer 7 SNAT
TCP CAS 443 Layer 7 SNAT
TCP HT 25 Used for the HT (Hub Transport) role Layer 4 DR (Direct Routing – Ultra-fast, local server based load balancing) Layer 4 NAT (Fast Load balancing throughput) Layer 7 SNAT (Flexible, URL switching and cookie insertion capabilities)
TCP CAS 110, 995,
143, 993,
135, 60201
Used for POP3 clients Used for IMAP4 clients RPC endpoint mapper Static port for Exchange address book service Layer 7 SNAT

FAQs

  • What parts of Microsoft Exchange do I need to load balance?

    In Exchange 2010, key functionality is split into 3 roles: Mailbox Server, Client Access Server and Hub Transport Server. In Exchange 2013, roles were consolidated into Client Access Server and Mailbox Server. In Exchange 2016, primary functionality was consolidated into a single role - the Mailbox Server. For all versions of Exchange, the load balancer is used to load balance all required client connection protocols, as well as inbound SMTP connections.

  • Do I need to enable persistence on the load balancer?

    For Exchange 2013 & 2016, all sessions to the CAS servers are stateless and therefore persistence/affinity is no longer required on the load balancer. For Exchange 2010, some protocols require affinity and others don't as detailed here.

  • Can I offload SSL on the load balancer?

    The load balancer fully supports SSL termination and backend server re-encryption. SSL offloading for Exchange 2013 and later is supported from 2013 SP1 as detailed here. However, for scalability and effective load sharing we recommend terminating SSL on the Exchange Servers rather than on the load balancer. Note that if you're load balancing Exchange using layer 7 SNAT mode, by default, the client IP address will be lost and replaced by the load balancer's own IP and therefore audit logs will contain the load balancer's IP address and not the clients. If this is an issue for your environment, X-Forwarded-For headers can be inserted by the load balancer which enable IIS on each Exchange server to be configured to log the client address from the XFF header as described here. In this case, SSL must be terminated on the load balancer to allow the header to be inserted. Once inserted, traffic can be reencypted from the load balancer to the Exchange servers.

  • Can I deploy across Multiple Data Centers?

    For a detailed look at deploying across multiple data centers, please refer to this blog.

Surely you must have a question?