Dell Force10 Z9000 - Hash-Algorithm D

The different hash algorithms are based on the number of Port Channel members and packet
values. The default hash algorithm (number 0) yields the most balanced results in various test
scenarios, but if the default algorithm does not provide a satisfactory distribution of traffic, use
the hash-algorithm command to designate another algorithm.
When a Port Channel member leaves or is added to the Port Channel, the hash algorithm is
recalculated to balance traffic across the members.
On TeraScale, if the keyword ECMP or LAG is not entered, FTOS assumes it to be common for
both. If the keyword ECMP orLAG is entered separately, both fall in the range of 0 to 23 or 24 to
47 because compression enable/disable is common for both keywords.
TeraScale and ExaScale support the range 0 to 47. The default for ExaScale is 24.
Related
Commands
load-balance (E-Series) – Change the traffic balancing method.
hash-algorithm d
Select the d value for the ECMP, LAG, and NH hashing algorithm.
E-Series
Syntax
hash-algorithm d value [linecard slot] [port-set number]
Parameters
d value Enter the keyword d followed by the d value. The range is 0 to 4095.
linecard slot Enter the keyword linecard followed by the linecard slot number.
port-set number Enter the keywords port-set followed by the linecard port-pipe
number.
Defaults none
Command Modes CONFIGURATION
Command History
Version 8.3.10.0 Introduced on the E-Series.
Usage
Information
Deterministic ECMP sorts ECMPs in order even though RTM provides them in a random order.
However, the hash algorithm uses as a d the lower 12 bits of the chassis MAC, which yields a
different hash result for every chassis. This means that for a given flow, even though the
prefixes are sorted, two unrelated chassis selects different hops.
FTOS provides a CLI-based solution for modifying the hash d to ensure that on each configured
system, the ECMP selection is same. When configured, the same d is set for ECMP, LAG, and
NH, and is used for incoming traffic only.
NOTE: While the d is stored separately on each port-pipe, the same d is used across all
CAMs.
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