"arp: %x:%x:%x:%x:%x:%x is using my IP address %d.%d.%d.%d!": ARP has discovered another host on the local network which responds to mapping requests for its own Internet address with a different Ethernet address, generally indicating that two hosts are attempting to use the same Internet address.
"arp: ether address is broadcast for IP address %d.%d.%d.%d!": ARP requested information for a host, and received an answer indicating that the hosts ethernet address is the ethernet broadcast address. This indicates a misconfigured or broken device.
"arp: %d.%d.%d.%d moved from %x:%x:%x:%x:%x:%x to %x:%x:%x:%x:%x:%x": ARP had a cached value for the ethernet address of the referenced host, but received a reply indicating that the host is at a new address. This can happen normally when host hardware addresses change, or when a mobile node arrives or leaves the local subnet. It can also indicate a problem with proxy ARP. This message can only be issued if the sysctl net.link.ether.inet.log_arp_movements is set to 1, which is the systems default behaviour.
"arpresolve: cant allocate llinfo for %d.%d.%d.%d": The route for the referenced host points to a device upon which ARP is required, but ARP was unable to allocate a routing table entry in which to store the hosts MAC address. This usually points to a misconfigured routing table. It can also occur if the kernel cannot allocate memory.
"arp: %d.%d.%d.%d is on if0 but got reply from %x:%x:%x:%x:%x:%x on if1": Physical connections exist to the same logical IP network on both if0 and if1. It can also occur if an entry already exists in the ARP cache for the IP address above, and the cable has been disconnected from if0, then reconnected to if1. This message can only be issued if the sysctl net.link.ether.inet.log_arp_wrong_iface is set to 1, which is the systems default behaviour.
inet(4), route(4), arp(8), ifconfig(8), route(8), sysctl(8)