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Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

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Configuring the Hash Algorithm Seed

Deterministic ECMP sorts ECMPs in order even though RTM provides them in a random order. However, the hash algorithm uses as a seed the lower 12 bits of the chassis MAC, which yields a different hash result for every chassis.

This behavior means that for a given flow, even though the prefixes are sorted, two unrelated chassis can select different hops.

Dell EMC Networking OS provides a command line interface (CLI)-based solution for modifying the hash seed to ensure that on each configured system, the ECMP selection is same. When configured, the same seed is set for ECMP, LAG, and NH, and is used for incoming traffic only.

NOTE While the seed is stored separately on each port-pipe, the same seed is used across all CAMs.
NOTE You cannot separate LAG and ECMP, but you can use different algorithms across the chassis with the same seed. If LAG member ports span multiple port-pipes and line cards, set the seed to the same value on each port-pipe to achieve deterministic behavior.
NOTE If you remove the hash algorithm configuration, the hash seed does not return to the original factory default setting.

To configure the hash algorithm seed, use the following command.

Specify the hash algorithm seed.
CONFIGURATION mode.
hash-algorithm seed value [stack—unit stack—unit-number] [port-set number]
The range is from 0 to 4095.

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