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Command Modes CONFIGURATION
Supported Modes Full–Switch
Command
History
Version Description
9.9(0.0) Introduced on the FN IOM.
9.2(0.0) Introduced on the MXL 10/40GbE Switch IO Module.
Usage
Information
The hash value calculated with the hash-algorithm command is unique to the entire chassis. The
default ECMP hash configuration is crc-lower. This command takes the lower 32 bits of the hash key to
compute the egress port and is the “fall-back” configuration if you have not configured anything else.
The different hash algorithms are based on the number of ECMP group members and packet values.
The default hash algorithm yields the most balanced results in various test scenarios, but if the default
algorithm does not provide satisfactory distribution of traffic, use this command to designate another
algorithm.
When a member leaves or is added to the ECMP group, the hash algorithm is recalculated to balance
traffic across the members.
hash-algorithm seed
Select the seed value for the ECMP, LAG, and NH hashing algorithm.
Syntax
hash-algorithm seed value [linecard slot] [port-set number]
Parameters
seed value Enter the keyword seed then the seed value. The range is from 0 to 4095.
linecard slot Enter the keyword linecard then the linecard slot number.
port-set number Enter the keywords port-set then the linecard port-pipe number.
Defaults none
Command Modes CONFIGURATION
Supported Modes Full–Switch
Command
History
Version Description
9.9(0.0) Introduced on the FN IOM.
9.2(0.0) Introduced on the MXL 10/40GbE Switch IO Module.
Usage
Information
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 select different hops.
The Dell Networking OS provides a 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.
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.
If the hash algorithm configuration is removed, the hash seed does not go to the original factory
default setting.
Equal Cost Multi-Path (ECMP) 423