User-class and DHCPINFORM
Glenn Satchell
Glenn.Satchell at uniq.com.au
Thu Oct 15 22:20:48 UTC 2009
Hi Thomas
Usually it is an application, eg IE, causingthe DHCPINFORMs to try to
get proxy info. A workaround is to add the proxy info to the request
parameters so no DHCPINFORM is sent. This was sent a whilke ago, and I
use it in my dhcpd.conf:
# 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);
}
# 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";
The \000 adds a null byte on the end. In some unspecified
configurations windows chops off the last byte.
regards,
-glenn
--
Glenn Satchell mailto:glenn.satchell at uniq.com.au | Miss 9: What do you
Uniq Advances Pty Ltd http://www.uniq.com.au | do at work Dad?
PO Box 70 Paddington NSW Australia 2021 | Miss 6: He just
tel:0409-458-580 fax:02-9380-6416 | types random stuff.
>From: "DELFAIRIERE Thomas" <thomas.delfairiere at siih5962.fr>
>
>Hello,
>
>I've got XP workstations and DHCP servers configured with a user class like
this
>
>class "PCs_User_Class_Chrul" {
> match if (option user-class = "mycompany");
> option domain-name "mycompany.net";
>}
>
>In default network, the default domain-name option is "yyyy.com".
>
>Some workstations with good settings (user class "mycompany" in the paramaters
of the network interface) don't have the good domain-name (they have yyyy.com
instead of mycompany.net).
>
>I realize a sniff :
>- when a workstation (with the user-class "mycompany") send DHCPREQUEST or
DHCPDISCOVER, the dhcp server respond with the good domain-name "mycompany.net".
>- when the same workstation send DHCPINFORM, the dhcp server respond with the
default domain-name "yyyy.com".
>
>The rfc 2131 (4.3.1) explains that the user-class is interpreted by dhcp
server when receiving DHCPREQUEST or DHCPDISCOVER. Why the client send
DHCPINFORM and DHCP server responds without interpreting the user class?
>
>Is there a way to force the DHCP server to interpret the user class in the
DHCPINFORM message?
>
>Thanks for your ansvers
>
>
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