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

cuicui cuicui.oizo at free.fr
Tue Mar 28 13:12:46 BST 2006

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

All the best,


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