Reference Guide

Equal Cost Multi-Path (ECMP) | 343

Equal Cost Multi-Path (ECMP)

Equal Cost Multi-Path (ECMP) is supported on the S5000 switch.

This chapter contains the following sections:

• ECMP for Flow-based Affinity

• Managing ECMP Group Paths

ECMP for Flow-based Affinity

ECMP for Flow-based Affinity is available on the S5000 switch.

• Configuring Hash Algorithm Seed

• Link Bundle Monitoring

Configuring 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.

Dell Networking OS 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.

Note: IPv6 /128 routes having multiple paths do not form ECMPs. The /128 route is treated as a host

entry and finds its place in the host table.

Note: Using XOR algorithms will result in imbalanced loads across an ECMP/LAG when the number of

members in said ECMP/LAG is a multiple of 4.

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 stack units, 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.