Setup Guide

Equal Cost Multi-Path (ECMP)
This chapter describes conguring ECMP. This chapter describes conguring ECMP.
ECMP for Flow-Based Anity
ECMP for ow-based anity includes link bundle monitoring.
Conguring 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 dierent hash result for every chassis.
This behavior means that for a given ow, even though the prexes are sorted, two unrelated chassis can select dierent hops.
Dell EMC Networking OS provides a command line interface (CLI)-based solution for modifying the hash seed to ensure that on each
congured system, the ECMP selection is same. When congured, the same seed is set for ECMP, LAG, and NH, and is used for incoming
trac 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 dierent 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 conguration, the hash seed does not return to the original factory default setting.
To congure 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.
Link Bundle Monitoring
Link bundle monitoring allows the system to monitor the use of multiple links for an uneven distribution.
Monitoring linked ECMP bundles allows trac distribution amounts in a link to be monitored for unfair distribution at any given time. A
global default threshold of 60% is Link bundle monitoring allows the system to monitor the use of multiple links for an uneven distribution. .
Links are monitored in 15-second intervals for three consecutive instances. Any deviation within that time causes a syslog to be sent and an
alarm event generate. When the deviation clears, another syslog is sent and a clear alarm event generates. For example, link bundle
monitoring percent threshold: %STKUNIT0-M:CP %IFMGR-5-BUNDLE_UNEVEN_DISTRIBUTION: Found uneven
distribution in LAG bundle 11.
Link bundle utilization is calculated as the total bandwidth of all links divided by the total bytes-per-second of all links. Within each ECMP
group, you can specify interfaces. If you enable monitoring for the ECMP group, utilization calculation performs when the utilization of the
link-bundle (not a link within a bundle) exceeds 60%.
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346 Equal Cost Multi-Path (ECMP)