Steering Algorithms

The Steering Algorithms define how Adaptiv manages and distributes network traffic across multiple WAN links.

They control how connections are selected, balanced, or redirected when a link’s status or performance changes. Currently in Adaptiv Connect, we implemented 2 algorithms:

OPFA (Order Preferred First Algorithm): Active–Passive configuration
ETFA (Equalized Traffic First Algorithm): Active–Active configuration

When a path is set as a backup, these steering algorithms (OPFA/ETFA) will only use it if no other paths are available.

1. OPFA (Order Preferred First Algorithm)

OPFA (Order Preferred First Algorithm) ensures that the traffic will always use the highest-priority active link.
The OPFA selects links based on the order of IP address pools. The first pool in the list is the primary (preferred) link. If that link becomes unavailable, OPFA automatically switches to the next pool in order - the secondary (standby) link, maintaining session continuity.

OPFA operates in an Active–Passive mode:

The primary link carries all traffic
The secondary link remains idle until a failure occurs.

This design ensures stability and predictable routing behaviour.

Example — SMTP Traffic using OPFA

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acl nat in +tcp 1 +194.204.1.3/32:0-0 +any:25-25 +nat poolip:1,10 opfa

In this Adaptiv deployment configuration example, the rule for port 25 (SMTP - Simple Mail Transfer Protocol) routes traffic from the internal mail server (with IP address 194.204.1.3) through the OPFA steering algorithm.
The NAT pool poolip:1,10 provides 2 link options:

1 - Primary link
10 - Secondary (standby) link.

If the primary is operational, OPFA will send all of the traffic over this primary link. The secondary link remains inactive and only becomes active during a failure.
If the link 1(the primary link) fails, OPFA automatically switches to link 10 (the secondary/standby link), ensuring the internal mail server continues operating without any session loss.

2. ETFA (Equalized Traffic First Algorithm)

The ETFA ( Equalized Traffic First Algorithm) provides Active–Active load balancing by distributing traffic dynamically across multiple links based on real-time utilization.

2.1. Load Balancing behaviour

Unlike OPFA, ETFA continuously uses all available links to maximize bandwidth efficiency.
ETFA evaluates each link’s inbound and outbound bandwidth usage, configured thresholds, and operational status (link status: up/down).
If two links have similar utilization, ETFA distributes traffic evenly and sequentially between the available resources (WAN links) in a round-robin method to maintain balance.

2.2. How ETFA makes a decision — The Equalized Traffic First Algorithm will make its link selection using the following criteria:

Incoming utilization - current inbound usage (%).
Outgoing utilization - current outbound usage (%).
Incoming threshold - The configured maximum limit for inbound usage; if reached, the link is deprioritized.
Outgoing threshold - The configured maximum limit for outbound usage; if reached, the link is deprioritized.
Link status – Only links that are up and healthy are selected. (Status: Up or Down)

In Adaptiv Connect, the system defaults the threshold to 90% of the link capacity, ensuring automatic load balancing and preventing overload.

Example - HTTP Traffic using ETFA

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acl nat in +tcp 2 +194.204.1.3/32:0-0 +any:80-80 +nat poolip:1,10 etfa

In this Adaptiv deployment configuration example, the rule for port 80 (HTTP) routes traffic from the internal server 194.204.1.3 through the ETFA steering algorithm.

The NAT pool poolip:1,10 provides both WAN link options for load balancing.
ETFA actively evaluates and selects both links in real time and sends traffic to the least-utilized link. For more details:

Incoming/Outgoing Utilization
- Link 1 = 70% inbound utilization & 65% outbound utilization.
- Link 10 = 45% inbound utilization & 50% outbound utilization.
  In this case, Link 10 is less utilized overall → ETFA will prefer Link 10 for new HTTP connections to balance traffic and prevent sending traffic to Link 1.
Threshold behavior
- The configured threshold = 90%.
- If Link 1 reach 95% outbound utilization
- Link 10 is at 60%.
  → ETFA will redirect new HTTP sessions to Link 10 until Link 1's usage drops below the 90% threshold.
For Criteria 5 - Link Status
- If link 10 goes down.
- Link 1 is up.
  → ETFA automatically switches traffic to Link 1 (remaining active link), ensuring that HTTP sessions continue without interruption and bandwidth is used efficiently.

If both links have equal conditions and both of them are up → the traffic is distributed round-robin between them to maintain the load balance.