Users Guide

ipv6 ecmp-deterministic
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 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 number] [port-set number]
The range is from 0 to 447483646.
Link Bundle Monitoring
Monitoring linked ECMP bundles allows trac distribution amounts in a link to be monitored for unfair distribution at any given time.
A default threshold of 60% is dened as an acceptable amount of trac on a member link. Links are monitored in 15-second intervals
for three consecutive instances. Any deviation within that time sends a syslog and generates an alarm event. 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 specied. 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 congures 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 congured. This is dierent from the ecmp-group index 2 that is created by
conguring routes and is automatically generated.
These two ecmp-groups are not related in any way.
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Equal Cost Multi-Path (ECMP)