Configuring The Hash Algorithm Seed; Link Bundle Monitoring - Dell S4048T Configuration Manual

• Enable IPv6 Deterministic ECMP next hop.
CONFIGURATION mode.
ipv6 ecmp-deterministic

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,
Equal Cost Multi-Path (ECMP) 369