Reference Guide

Equal Cost Multi-Path (ECMP) | 265

Equal Cost Multi-Path (ECMP)

Equal Cost Multi-Path (ECMP) is supported on the following platforms: s z

• Configurable Hash Algorithm Seed

• Link Bundle Monitoring

• Managing ECMP Group Paths

Configurable 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 means that for a given flow, even though the prefixes are sorted, two unrelated

chassis will select different hops.

FTOS provides a 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.

Link Bundle Monitoring

Link Bundle Monitoring is supported only on platforms z

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 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 the hash algorithm configuration is removed. Hash seed will not go to original factory default

setting.

Task Command Syntax Command Mode

Specify the hash algorithm seed. hash-algorithm seed value [stack-unit number]

[port-set number]

Range: 0 - 4095

CONFIGURATION