Bandwidth Aggregation and Application Load-Balancing
There are many different use cases that demand changes to the way WANs are handled today. Some are as simple as businesses wanting bandwidth aggregation. This is the ability to use both public and private transports together at the same time. This is what is considered using A + B versus A or B, meaning the secondary transport link (Link B) usually sits idle without any traffic using it until Link A fails. However, in a hybrid WAN approach, being able to leverage multiple links at the same time provides an ability to use bandwidth from both links. This is considered an A + A or an Active/Active scenario. Application load-balancing is achieved using these types of designs as well. This type of hybrid environment allows for greater application performance at a fraction of the cost of two premium transport links. This also increases scale and flexibility without any security compromise. Figure 1-8 illustrates the various options of application load-balancing over multiple links in a hybrid environment. You can see that, by default, per-session Active/Active load-sharing is achieved. Weighted per-session round-robin is also configurable on a device basis. Application pinning, or forcing an application to take a specific transport, is also something that can be enforced via policy. Similarly, Application-Aware Routing or SLA-compliant routing is achieved by enforcing a policy that looks for specific traffic characteristics such as jitter, loss, and delay to determine the path the application should take over the available transports.
FIGURE 1.8 Application Load-Balancing Options