file: /proc/sys/net/ipv4/conf/interface/arp_accept
variable: net.ipv4.conf.interface.arp_accept
Official reference

Define behavior for gratuitous ARP frames who’s IP is not already present in the ARP table: 0 - don’t create new entries in the ARP table 1 - create new entries in the ARP table

Both replies and requests type gratuitous arp will trigger the ARP table to be updated, if this setting is on.

If the ARP table already contains the IP address of the gratuitous arp frame, the arp table will be updated regardless if this setting is on or off.

Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.