Configuring The Hash Algorithm Seed; Link Bundle Monitoring - Dell S6000–ON Configuration Manual

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 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.
Equal Cost Multi-Path (ECMP)
309