[Dnsmasq-discuss] dhcp-option=252, ... (was: DNSmasq should warn when using unsupported dhcp option)

Matt Hull mhull1 at uic.edu
Tue Mar 28 21:46:20 BST 2006

On Tue, 28 Mar 2006, cuicui wrote:

> Simon Kelley wrote:
> > cuicui wrote:
> >> Hi everybody,
> >>
> >> I'm new on this list, i use the dhcp side of dnsmasq on a private
> >> network to manage 40 win2k computers with restricted access (and
> >> static addressing).
> >>
> >> Today i tried to use the #252 dhcp option that allow to
> >> (indirectly) configure proxy options on workstations, this option
> >> doesn't give the proxy adress/port but the URL of an
> >> auto-configuration script that gives proxy settings.
> >>
> >> dhcp-option=252,http://myserv.er/proxy.pac
> >>
> >> It didn't work, so i made a network capture with Ethereal to see
> >> which DHCP options were really send during the DHCP dialog and the
> >> #252 option was missing.
> >>
> >> After a quick look a the sources it *seems* that this option is not
> >>  implemented yet. As far as dnsmasq was starting fine even with a
> >> dhcp configuration it didn't support, i think it could be a good
> >> idea to write a warning to syslog in this kind of case, just to
> >> inform which dhcp options will be dropped.
> >>
> >
> > There's no such thing as an unsupported DHCP option: dnsmasq parses
> > the stuff to the right of the equals sign in "dhcp-option=" and turns
> > it into a set of bytes which is sent. The most common data types are
> >  supported with code to turn them into bytes (ie strings, IP
> > addresses) but with a few exceptions, the data type is determined
> > from the data, not from the option number. In any case it's always
> > possible to exactly control what is sent by giving the bytes directly
> > in hex.
> Well, that's good new! It *seems* i was a little wrong on my diagnostic :)
> > Did your DHCP client ask for the value of option 252?  Look for
> > "requested options" in the DHCPDISCOVER and DHCPREQUEST packets. Most
> >  likely it isn't asking, which is why it doesn't get send. Windows
> > often asks for WPAD info later, using a DHCPINFORM request. I assume
> > that is generated by the browser, not the networking subsystem.
> I'll check that as soon as i can. I'm pretty sure i'll have to do some
> tricks to make Win2K ask for this particular option and make it work
> once it'll get it.
> I know this is off-topic but if somebody here succeed with sending proxy
> auto-configuration script with dnsmasq for win2k workstations, i'll take
> any advices, unfortunately a cannot use special DNS entries but my
> autoconf script works fine when i manually set it on IE's connexion
> settings.
> All the best,
> Nicolas

instead of setting each of the 40 computers to a proxy, perhaps you could
use the server to that ?  i know that is off topic and what you are doing
should work, but thought i would suggest an alternative.


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