interface aliases with the fxp driver

[Chris Boyd]

While setting up a server with several IP addresses on the same
interface, we noticed something a bit odd.

When we add the new IP address with the command
  ifconfig fxp0 alias 192.168.12.100 netmask 255.255.255.255

We can ping the address and all seems well at first.  Then apparently
the other machines' ARP caches time out, and the 192.168.12.100 IP
address is no longer reachable on the LAN.

tcpdump confirms that the server is not responding to ARP requests.

Adding the arp keyword to the ifconfig command seems to fix things.
   ifconfig fxp0 alias arp 192.168.12.100 netmask 255.255.255.255

Works as we'd expect.

This was observed on 4.9-RELEASE and 4.10-STABLE

I've not tried it on boxes with other kinds of Ethernet cards yet.

Is this normal, or a bug in the fxp driver?

Thanks!

--Chris