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Dell EMC Networking OS allows you to modify the hashing algorithms used for flows and for fragments. The load-balance and
hash-algorithm commands are available for modifying the distribution algorithms.
Load-Balancing Method
By default, LAG hashing uses the source IP, destination IP, source transmission control protocol (TCP)/user datagram protocol
(UDP) port, and destination TCP/UDP port for hash computation. For packets without a Layer 3 header, Dell EMC Networking
OS automatically uses load-balance mac source-dest-mac.
Do not configure IP hashing or MAC hashing at the same time. If you configure an IP and MAC hashing scheme at the same
time, the MAC hashing scheme takes precedence over the IP hashing scheme.
To change the IP traffic load-balancing default, use the following command.
● Replace the default IP 4-tuple method of balancing traffic over a port channel.
CONFIGURATION mode
[no] load-balance {ip-selection [dest-ip | source-ip]} | {mac [dest-mac | source-dest-mac
| source-mac]} | {tcp-udp enable} {ipv6-selection} {tunnel}| {ingress-port}
You can select one, two, or all three of the following basic hash methods:
○ ip-selection [dest-ip | source-ip] — Distribute IP traffic based on the IP destination or source address.
○ mac [dest-mac | source-dest-mac | source-mac] — Distribute IPV4 traffic based on the destination or
source MAC address, or both, along with the VLAN, Ethertype, source module ID and source port ID.
○ tcp-udp enable — Distribute traffic based on the TCP/UDP source and destination ports.
○ ingress-port — Option to Source Port Id for ECMP/ LAG hashing.
○ ipv6-selection— Set the IPV6 key fields to use in hash computation.
○ tunnel— Set the tunnel key fields to use in hash computation.
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 traffic 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 {algorithm-number | {ecmp {crc16 | crc16cc | crc32MSB | crc32LSB | crc-
upper | dest-ip | lsb | xor1 | xor2 | xor4 | xor8 | xor16} [number] hg {crc16 | crc16cc
| crc32MSB | crc32LSB | xor1 | xor2 | xor4 | xor8 | xor16} stack-unit stack-unit-number |
port-set port-pipe | hg-seed seed-value stack-unit | lag {checksum | crc | xor} [number]
nh-ecmp {checksum | crc | xor}[number] stack—unit number ip-sa-mask value ip-da-mask
value | seed seed-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 the Hash algorithm seed value to get better hash value
Hash seed is used to compute the hash value. By default hash seed is chassis MAC 32 bits. we can also change the hash
seed by the following command.
CONFIGURATION mode
hash-algorithm seed {seed value}
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