What Is Adaptive Routing Tuning?

Why Do We Need ART?

Traditional load balancing selects routes randomly or based on the hash algorithm, without considering the link quality of each member link. As a result, load balancing may be uneven.

Improving on the original load balancing mechanism, ART selects paths based on the congestion status of member links. It preferentially selects light-load paths and avoids congested paths, maximally ensuring load balancing among member links.

How Does ART Achieve Better Load Balancing?

ART classifies device traffic into two types: per-packet traffic and per-flow traffic. ART optimizes load balancing for per-packet traffic. For per-flow traffic, the device uses the traditional ECMP static load balancing mode for route selection. Specifically, the device performs hash-based route selection based on information such as the 5-tuple of packets, without considering the congestion status of interfaces.

The route selection principles for load balancing of per-packet traffic are as follows:

1. The device searches the routing table for all outbound interfaces and calculates the queue buffer depths (queue buffer sizes) of these interfaces to determine their congestion levels.

   A device can classify queue buffer depths into multiple congestion levels. A higher level indicates more severe congestion. Each congestion level corresponds to a congestion level threshold range, as listed in the following table.

   Table 1-1 Congestion levels and their threshold ranges

   Congestion Level Threshold Range (X: Queue Buffer Depth; TH0 to TH14: Upper and Lower Limits of the Congestion Level Threshold)	Congestion Level
   X < TH0	0
   TH0 ≤ X < TH1	1
   TH1 ≤ X < TH2	2
   ...	...
   TH13 ≤ X < TH14	14
   TH14 ≤ X	15

2. The device selects some outbound interfaces based on the ECMP per-packet load balancing algorithm, and then selects one of these interfaces as the outbound interface.
   • If the interfaces have different congestion levels, the device selects the interface with the lowest congestion level as the outbound interface.
   • If the congestion levels are the same, the device uses the internal algorithm to select one of these interfaces as the outbound interface.