Bug #115487 - automatic proxy discovery problems

Travers Carter tcarter at noggin.com.au
Fri Jun 4 02:11:49 BST 2010

On Thu, 3 Jun 2010 07:12:43 Dawit A wrote:
> It never was at least not in a portable way and that is probably why even
> Firefox does not support the DHCP based approach for WPAD. At least it did
> not before, no idea if that has changed recently.[1]

I believe that is still the case, as far as I can find Firefox simply makes a 
single request for http://wpad/wapd.dat and relies on the resolver to append 
the appropriate domain.  DHCP Discovery has been requested but not implemented 
- https://bugzilla.mozilla.org/show_bug.cgi?id=356831

> That would assume that NetworkManager is used everywhere you want to do
> this. That will not be the case. For example, it won't work on my machine
> as I do not use NetworkManager.

Sure, that's why I was thinking routing lookup.

> Personally, the DHCPINFORM look-up approach should be completely abandoned
> as an option for doing WPAD just almost all other major browsers
> (exception being IE). That feature should solely rely on the more reliable
> DNS based auto proxy discovery method. Even if you were somehow to come up
> with a way to do this in a semi-portable manner, you will have other
> issues such as multi-homed machines (which interface's ip address to use)
> etc ; so I rather doubt it is worth doing...

Using a route lookup should yield the correct result on multi-homed hosts, 
since it asks the kernel for what source address it would use when it sends a 
packet to, but it's clearly not a portable solution and would 
leave non-linux systems using the existing unreliable approach unless someone 
else implemented a similar solution for them (eg I believe BSD has a similar 
route API to linux netlink).

I suppose since Firefox doesn't support DHCPINFORM lookups and there hasn't 
been much complaint about that I guess you can infer it's not exactly a 
critical feature.

I am willing to have a go at implementing netlink route lookups on linux, but 
DHCPINFORM discovery isn't critical for me since my networks support both 
DHCPINFORM and DNS discovery, so if the consensus is that the DHCPINFORM 
support should be dropped I won't bother.

Travers Carter

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