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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.
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: %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%.
Enable link bundle monitoring using the ecmp-group command.
NOTE:
An ecmp-group index is generated automatically for each unique ecmp-group when you configure multipath routes
to the same network. The system can generate a maximum of 512 unique ecmp-groups. The ecmp-group indexes are
generated in even numbers (0, 2, 4, 6... 1022) and are for information only.
For link bundle monitoring with ECMP, to enable the link bundle monitoring feature, use the ecmp-group command. In the
following example, the ecmp-group with id 2, enabled for link bundle monitoring is user configured. This is different from the
ecmp-group index 2 that is created by configuring routes and is automatically generated.
These two ecmp-groups are not related in any way.
Example of Viewing Link Bundle Monitoring
DellEMC# show link-bundle-distribution ecmp-group 1
Link-bundle trigger threshold - 60
ECMP bundle - 1 Utilization[In Percent] - 44 Alarm State - Active
Interface Line Protocol Utilization[In Percent]
Gi 1/1 Up 36
Gi 1/1 Up 52
266
Equal Cost Multi-Path (ECMP)