Manually configuring outbound traffic management

Outbound Multi-Link elements combine NetLinks and set options for the high availability and load balancing features.

NetLink selection for load balancing can be based on either of two methods:
  • Round Trip Time — The Engine periodically probes NetLinks for speed and selects the fastest active NetLink for each new outbound connection. For each new TCP connection, the Engine sends the initial SYN request through all available NetLinks and measures link performance. The NetLink that receives the SYN-ACK reply first establishes the TCP connection, and the Engine cancels the remaining attempts by sending a TCP Reset (RST) through the other NetLinks.

    The fastest route is automatically selected for each connection. Information about the performance of each NetLink is cached, so no new measurement is made if a new connection is opened to the same destination within a short time period.

    To use the round trip time method, you must configure the probing settings in the Static NetLink or Dynamic NetLink properties.

  • Ratio — Traffic is distributed across all active NetLinks according to their relative bandwidth. The NetLink with the highest bandwidth handles the largest portion of traffic, and the remaining NetLinks are assigned proportional shares based on their bandwidth relative to the highest.

    When the volume of traffic is low, the ratio of actual traffic distribution is approximate. When the volume of traffic is high, the ratio of traffic handled by each NetLink is closer to the ratio calculated from the link capacity.

You can optionally assign QoS Classes to NetLinks in the Outbound Multi-Link element to specify which traffic is routed through which NetLink. NAT rules can alternatively be used to select a particular link, but if you use QoS Classes, traffic can still fail over to other links if the selected link fails.

The same QoS class can be assigned to multiple NetLinks within the same Outbound Multi-Link element to balance traffic across those NetLinks when they are available. To specify which traffic uses which NetLink using a QoS class, you must assign the QoS class to the traffic in an Access rule or through QoS policies based on the DSCP codes in the traffic.

To manually configure outbound traffic management, follow these general steps:

  1. Create an Outbound Multi-Link element to group your NetLinks and define traffic management settings.
  2. In the Engine Policy, create NAT rules for outbound load balancing.