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ARP monitoring sends ARP queries and uses the response as an indication that the link is operational. The ARP replies are not validated, so any received packet by the slave interface will result in the slave interface considered as active. This gives assurance that traffic is actually flowing over the links. If balance-rr and balance-xor modes are set, then the switch should be configured to evenly distribute packets across all links. Otherwise, all replies from the ARP targets will be received on the same link which could cause other links to fail. ARP monitoring is enabled by setting three properties - link-monitoring, arp-ip-targets and arp-interval. The meaning of each option is described later in this article. It is possible to specify multiple ARP targets that can be useful in High Availability setups. If only one target is set, the target itself may go down. Having additional targets increases the reliability of the ARP monitoring.
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