do not respond to DHCPINFORM requests

Glenn Satchell glenn.satchell at uniq.com.au
Thu May 9 11:21:50 UTC 2013


Hi Sergey and Randall

Several years ago I added this to my dhcpd.conf to try to work around one
cause of dhcpinform: the browser querying for wpad options. Not sure if
the \000 is still needed, but it does no harm. In the comments PRL is the
"parameter request list".

# Windows systems accept the WPAD option for setting up their proxy server
# (Autodetect proxy settings):
# (According to Ted Lemon, "text" will get the Microsoft
# NUL termination bug heuristic applied, and "string" won't!
option wpad code 252 = text;
option wpad "http://proxy/proxy.pac\000";

# Special config for Windows ("MSFT 5.0") systems.
# Note this does not catch Windows CE.
class "MSFT" {
  match if substring(option vendor-class-identifier, 0, 4) = "MSFT";
  # They put 252 on the DHCPINFORM's, but not on the DHCPREQUEST's
  # PRL.  So we over-ride the PRL to include 252 = 0xFC, which will
  # send the option at DHCPDISCOVER/DHCPREQUEST time, and wil also
  # suppress the DHCPINFORMS!  They seem to cache it.
  option dhcp-parameter-request-list = concat(option
dhcp-parameter-request-list, fc);
}

regards,
-glenn

On Thu, May 9, 2013 9:44 am, Sergey Skobkarev wrote:
> Hi Randall,
>
> I'm having the same problem with 'custom' groups inside subnets. Windows 7
> machines successfully get IP, domain, DNS server and other parameters on
> IP renew, but then they (IE?) send DHCPINFORM request, receive wrong DNS
> server and domain information and "fix" their lease details. As a result,
> I cannot assign proper 'custom' options.
>
> If I remove 'authorative' from the configuration file, dhcpd stops
> responding to DHCPINFORM requests, so it works as a temporary solution.
> However, I however have some other usage for DHCPINFORM's and would like
> to fix the server and get proper INFORM answers.
>
> I was going to hack the code, but then saw your message and decided to ask
> if you succeeded in that already and if you did, would you send me a patch
> or at least point out where should I start?
>
> My DHCP server's version is 4.1.1 (Release: 34.P1.el6.centos), but I'll
> probably use the latest code for hacking/recompiling.
>
> Thank you,
>
>
> --
> Sergey Skobkarev
>
>
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