Administrator 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 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 number] [port-set number]
The range is from 0 to 4095.
Link Bundle Monitoring
Monitoring linked ECMP bundles allows traffic distribution amounts in a link to be monitored for unfair distribution at any
given time. A default threshold of 60% is defined as an acceptable amount of traffic on a member link. 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 to be generated. When the deviation clears, another syslog is sent and a clear alarm event is generated. for example Link
bundle monitoring percent threshold %STKUNIT0-M:CP %IFMGR-5-BUNDLE_UNEVEN_DISTRIBUTION: Found uneven
distribution in LAG bundle 11..
The 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, interfaces can be specified. If monitoring is enabled for the ECMP group, the utilization calculation is
performed 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 the user configures 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, the ecmp-group command is used to enable the link bundle monitoring feature. 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
Dell# 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]
Te 1/1 Up 36
Te 1/1 Up 52
Managing ECMP Group Paths
Configure the maximum number of paths for an ECMP route that the L3 CAM can hold to avoid path degeneration. When you
do not configure the maximum number of routes, the CAM can hold a maximum ECMP per route.
Equal Cost Multi-Path (ECMP)
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