Re: Can we make NM automatically handle the need for proxy arp?

[Ted Lemon <mellon fugue com>]

On Aug 27, 2006, at 2:41 PM, Darren Albers wrote:
> So maybe Windows isn't brain dead and it is just my router  ;-)
>
> I have a new linksys sitting here and when my wife goes to bed I will
> swap it out and see if the behavior is correct.
>
> So the real question is (and off topic for this list since it isn't NM
> that is causing this) should linux networking treat a bad default
> gateway as no gateway and use proxy-arp?

Hm.  I would argue that it actually is appropriate for NM to do it,  
because NM is at the UI level, and you really want this to be a  
controllable behavior.   For example, one good UI for this would be to  
pop up a widget that says "yo, the DHCP server is giving bad  
information" and give the user the option of "Try ignoring this  
server" or "Try to make it work anyway."   Or you could make the  
behavior invisible to the user by having the DHCP client try to find a  
different DHCP server, and if it failed, only then try the  
workaround.   You would probably want to have a configuration  
parameter to control it - the current ISC client gives you the option  
of putting a bad DHCP server on a reject list.

You really want route add <bogus route> to print an error, and it  
wouldn't do that if you installed the workaround in the kernel.   Then  
you're going to get cases where a user manually mistypes the router IP  
address and doesn't get any feedback, and wastes twenty minutes  
debugging the problem.   Also, if you do the workaround in the kernel,  
you still need a UI to control that behavior, and NM is a fairly  
logical place to put it.   :')

Anyway, noname routers with weird DHCP implementations and weird ARP  
behavior are a well-known problem.   We've run into problems in the  
past where Macs, which follow RFC2131 more closely than any of the  
other DHCP implementations, will see a bogus proxy arp reply from a  
wireless gateway and send a DHCPDECLINE.   So it wouldn't surprise me  
if swapping out that router clears up the particular symptom you're  
talking about.