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Configure Flowset Table Size in DLB Flowlet Mode
Overview
Dynamic load balancing (DLB) is a load balancing technique that selects an optimal egress link based on link quality so that traffic flows are evenly distributed. You (the network administrator) can configure DLB in flowlet mode.
In flowlet mode, DLB tracks the flows by recording the last seen timestamp and the egress interface that DLB selected based on the optimal link quality. DLB records this information in the flowset table allocated to each ECMP group. The DLB algorithm maintains a given flow on a particular link until the last seen timestamp exceeds the inactivity timer. When the inactivity timer expires for a particular flow, DLB rechecks whether that link is still optimal for that flow. If the link is no longer optimal, DLB selects a new egress link and updates the flowset table with the new link and the last known timestamp of the flow. If the link continues to be optimal, the flowset table continues to use the same egress link.
You (the network administrator) can increase the flowset table size to change the distribution of the flowset table entries among the ECMP groups. The more entries an ECMP group has in the flowset table, the more flows the ECMP group can accommodate. In environments such as AI-ML data centers that must handle large numbers of flows, it is particularly useful for DLB to use a larger flowset table size. When each ECMP group can accommodate a large number of flows, DLB achieves better flow distribution across the ECMP member links.
The flowset table holds 32,768 total entries, and these entries are divided equally among the DLB ECMP groups. The flowset table size for each ECMP group ranges from 256 through 32,768. Use the following formula to calculate the number of ECMP groups:
32,768/(flowset size) = Number of ECMP groups
By default, the flowset size is 256 entries, so by default there are 128 ECMP groups.
Benefits
Improve load distribution over egress links.
Group flows to minimize how many calculations DLB has to make for each flow.
Customize flowset table entry allocation for maximum efficiency.
Increase the efficiency of flowlet mode.
Configuration
Be aware of the following when configuring the flowset table size:
When you change the flowset size, the scale of ECMP DLB groups also changes. Allocating a flowset table size greater than 256 reduces the number of DLB-capable ECMP groups.
When you commit this configuration, traffic can drop during the configuration change.
DLB is not supported when a link aggregation group (LAG) is one of the egress members of ECMP.
Only underlay fabrics support DLB.
QFX5240 switch ports with a speed less than 50 Gbps do not support DLB.
Platform Support
See Feature Explorer for platform and release support.
