dhcpinform request from Vista gets wrong Name servers

Sten Carlsen sten at s-carlsen.dk
Wed Aug 15 18:54:30 UTC 2007

How about going from general  to specific?

Consider options mentioned in global scope first, then look more
specific places like subnet declarations, range declarations and host
declarations. Each time an option is encountered replace whatever was
picked up by the new value, that should make things work as expected.

E.g. parsing dhcpinform would pick up the general DNS option and when
the specific subnet matching this client is parsed, the value specific
to that subnet is now placed in the packet. This means that you will get
the generic value if no more specific is defined.

David W. Hankins wrote:
> On Wed, Aug 15, 2007 at 12:05:16PM -0400, Randall C Grimshaw wrote:
>> The Vista machines initially get the correct DNS settings and query for isatap (which resolves to the registration system) then queries for teredo.ipv6.microsoft.com (which resolves to the registration system).... then the rub... the Vista machine will perform a dhcpinfo query for name servers among other things and get the default name servers in the dhcpack - the default (production) name servers cannot be reached from the captive subnets and wouldn't direct users to the registration system if they were.
>> I am not sure if this is a bug in ISC dhcp by RFC or not.
> It's (very) cloudy.  The final answer is that ISC DHCP should provide
> the nameservers you /want/ it to provide in DHCPINFORM.  We don't.
> I would say we need to update ISC DHCP to address this, but I'm not
> precisely sure how...an exclusion list of 'things not to send in
> DHCPINFORM', sourcing the client's active binding in DHCPINFORM to
> bring in all that you know about it...
>> Does snyone know if the dhcpinfo is a response to unexpected answer to the other two queries?
> It's hard to say...Windows boxes (XP and Vista alike) will DHCPINFORM
> for many reasons, none of them can be reliably predicted (windows
> updater, Flash Proxy Autodetection, etc).

Best regards

Sten Carlsen

No improvements come from shouting:


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