arp -s reports a weird error “cannot allocate memory” when instructed to masquerade an ARP - IP entry whose IP is out of the local network window (e.g. 172.31.1.0 on a 172.31.0.0/24 network).

It would be more informative for the user to have the error reported as an “out of range IP” or something of the same ilk, since “cannot allocate memory” gives the false impression something is broken within the kernel.