Sepherosa Ziehau has introduced a new sysctl:

net.link.ether.inet.log_arp_creation_failure

Set this to zero and you won’t get endless ARP events from networks you aren’t on.  For example, I’m hooked up to a cable modem.  I only get a public routable IP address, but the network used for the cable modem network itself bleeds ARP packets out where my DragonFly machine can see it.  Since it’s on a different network segment than the address I receive through DHCP, it always fails and the system logs it.  For example:

May 11 05:20:52 www kernel: arplookup 100.68.112.145 failed: host is not on local network

I can’t do much about it since that layer 2 leakiness is going to happen, but I can shut it up with this sysctl – and thank goodness, cause I’ve been seeing these messages since first using a DOCSIS modem in… 2001 or so?