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Comment: Seemed useful to include this info from RN-826, in this doc for context.


It is useful to have a unique hash seed for each switch. This helps avoid hash polarization, a type of network congestion that occurs when multiple data flows try to reach a switch using the same switch ports. 


Starting in Cumulus Linux 3.5.4, if the ecmp_hash_seed value is not set in /etc/cumulus/datapath/traffic.conf (the default as shipped), switchd will use a randomly generated seed, which is stable across switchd restarts and reboots.

The hash seed is set by the ecmp_hash_seed parameter in the /etc/cumulus/datapath/traffic.conf file. It is an integer with a value from 0 to 4294967295. If you don't specify a value for it, switchd creates a randomly generated seed instead.