Concept Guide

Dell EMC Networking OS allows you to modify the hashing algorithms used for ows and for fragments. The load-balance and hash-
algorithm commands are available for modifying the distribution algorithms.
Changing the Hash Algorithm
The load-balance command selects the hash criteria applied to port channels.
If you do not obtain even distribution with the load-balance command, you can use the hash-algorithm command to select the
hash scheme for LAG, ECMP and NH-ECMP. You can rotate or shift the 12–bit Lag Hash until the desired hash is achieved.
The nh-ecmp option allows you to change the hash value for recursive ECMP routes independently of non-recursive ECMP routes. This
option provides for better trac distribution over available equal cost links that involve a recursive next hop lookup.
To change to another algorithm, use the second command.
• Change the default (0) to another algorithm and apply it to ECMP, LAG hashing, or a particular line card.
CONFIGURATION mode
hash-algorithm {ecmp {crc16 | crc16cc | crc32MSB | crc32LSB | crc-upper | dest-ip | flow-
based-hashing {crc16|crc16cc|crc32MSB|crc32LSB|xor1|xor2|xor4|xor8|xor16}|lsb | xor1 | xor2 |
xor4 | xor8 | xor16}[[hg {crc16 | crc16cc | crc32MSB | crc32LSB | xor1 | xor2 | xor4 | xor8 |
xor16}]| [lag {crc16 | crc16cc | crc32MSB | crc32LSB | xor1 | xor2 | xor4 | xor8 | xor16 }]
[stack-unit|linecard number | port-set number | [hg—seed seed-value | seedseed-value
For more information about algorithm choices, refer to the command details in the IP Routing chapter of the Dell EMC Networking OS
Command Reference Guide.
• Change to another algorithm.
CONFIGURATION mode
Example of the hash-algorithm Command
DellEMC(conf)#hash-algorithm ecmp xor 26 lag crc 26 nh-ecmp checksum 26
DellEMC(conf)#
The hash-algorithm command is specic to ECMP group. The default ECMP hash conguration is crc-lower. This command takes the
lower 32 bits of the hash key to compute the egress port. Other options for ECMP hash-algorithms are:
• crc16 — uses 16 bit CRC16-bisync polynomial
• crc16cc — uses 16 bit CRC16 using CRC16-CCITT polynomial
• crc32LSB — uses LSB 16 bits of computed CRC32
• crc32MSB — uses MSB 16 bits of computed CRC32(default)
• crc-upper — uses the upper 32 bits of the hash key to compute the egress port.
• dest-ip — uses destination IP address as part of the hash key.
• flow-based-hashing — uses ow-based-hashing followed by the algorithm crc16 |crc16cc |crc32MSB |crc32LSB |xor1 |xor2 |
xor4 |xor8 | xor16.
• lsb — uses the least signicant bit of the hash key to compute the egress port.
• xor1 — uses Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor1
• xor2 — Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor2
• xor4 —Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor4
• xor8 — Upper 8 bits of CRC16-BISYNC and lower 8 bits of xor8
• xor16 — uses 16 bit XOR.
Interfaces
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