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Introduction 27
Load Balancing and Link Failover
The NSE supports individual configuration of multiple WANs on an Access Gateway (supported on AG2400,
AG5600, AG5800, and AG5900 hardware). Hotels can use this capability in a number of ways, including load
balancing, failure protection, and subscriber allocation.
This section provides use cases and scenarios to help you consider the full advantage of these capabilities.
Definitions and Concepts
Load Balancing
Load balancing refers to the general process of balancing user traffic across multiple ISP connections. All
load-balancing appliances, as well as the Nomadix NSE, support load balancing.
Link Aggregation
Link aggregation refers to the process of connecting multiple ISP connections to an appliance and having the
sum of all of the ISP bandwidth available to be shared across all users.
However, one individual connection is limited to the speed of the ISP connection that is currently being used.
For example, a hotel may aggregate 5 x 1.5Mbps DSL connections together. This means that a total of
7.5Mbps of bandwidth is available to be shared across all users, but a single user can receive a maximum of
1.5Mbps. All load-balancing appliances, as well as the Nomadix NSE, support link aggregation. In most
cases, link aggregation and load balancing is effectively the same thing.
Link Failover
Link failover (sometimes referred to ISP redundancy) is the process of providing a second (or occasionally a
third or more) ISP link as a back up to the primary ISP link. In the event that the primary link fails, all traffic
is re-routed to the backup link, until such time as the primary link becomes available.
Combined Load Balancing and Link Failover
This is the process where both load balancing and link failover are combined together. It represents the best of
both worlds. Where multiple ISP links are used in load balancing mode, in the event that one or more links
fail, all traffic is automatically rerouted to the remaining surviving links. When the failed links recover, new
connections are routed toward these until the normal balanced configuration is reached.
ISP link Selection Criteria
In a load-balancing scenario, some criteria must be used to decide which ISP is selected for outgoing traffic.
There a number of factors that influence this decision, including:
 Identity of the users: Is a random ISP section used or is it desirable to have certain users steered
toward a particular ISP?

For random ISP: Whether subscriber, destination address or session-based link selection is used?
User-Based ISP Selection versus Random ISP Selection
User-based ISP selection is the process whereby the ISP link that is selected in a load-balanced environment is
based on the identity of the user. For example, all users from guest rooms may be steered toward one ISP link,
and all meeting room users steered toward another ISP link that is only used for meetings and conferences.
The alternative is to use random ISP selection, whereby the load balancer or NSE selects the ISP to be used
according to the current load conditions. The Nomadix NSE uses random ISP selection by default.