General Questions

I have 5 static IPs from my ISP and therefore use Proxy ARP.
Let say x.x.x.1 is the WAN IP and x.x.x.2, x.x.x.3, x.x.x.4, x.x.x.5 are the ProxyARP IPs.

My issue is that my ISP is a cable company and their modem occasionally drops one of my static IPs when the modem loses it's ARP-Cache.

What I need to be able to do is ping (or send traffic) FROM the m0n0wall using the WAN interface while specifying one of the ProxyARP IPs as the source so that IP re-registers with the ARP-Cache on the cable modem.

I can't use "ping" with the "-S" switch to specify the source address for any address except x.x.x.1 as the m0nowall doesnt bind the ProxyARP IPs to the WAN interface. (aka it errors with - ping: bind: Can't assign requested address)

Does anyone have any suggestions?

Ok so I added aliases for x.x.x.2, x.x.x.3, x.x.x.4, x.x.x.5 and now ping -S works as those x.x.x.2, x.x.x.3, x.x.x.4, x.x.x.5 IPs are bound to the WAN interface

Now I just have to figure out if those will stay on a reboot! 

The handbook section 15.10.1 says: Note that it is never necessary (and strongly discouraged) to use IP aliasing on the WAN interface (by means of ifconfig commands).

Can anyone explain WHY it is strongly discouraged?

I'd also like to know why it's strongly discouraged! Maybe because an alias is not tied to an IP address. So whoever has that IP on your WAN can do whatever the alias was granted within your router configuration. Nevertheless I don't realize why this should be a problem of WAN addresses exclusively.