Install Guide

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 [] [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 traffic 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:
Example of Viewing Link Bundle Monitoring
Managing ECMP Group Paths
To avoid path degeneration, configure the maximum number of paths for an ECMP route that the L3 CAM can hold. When you
do not configure the maximum number of routes, the CAM can hold a maximum ECMP per route.
To configure the maximum number of paths, use the following command.
NOTE:
For the new settings to take effect, save the new ECMP settings to the startup-config (write-mem) then reload
the system.
● Configure the maximum number of paths per ECMP group.
CONFIGURATION mode.
ip ecmp-group maximum-paths {2-64}
● Enable ECMP group path management.
CONFIGURATION mode.
ip ecmp-group path-fallback
DellEMC(conf)#ip ecmp-group maximum-paths 3
User configuration has been changed. Save the configuration and reload to take effect
DellEMC(conf)#
Equal Cost Multi-Path (ECMP)
267