Experience with answering option 252 with simple newline?
Jay Ford
jay-ford at uiowa.edu
Mon Sep 23 20:01:11 UTC 2013
On Mon, 23 Sep 2013, John Wobus wrote:
> We're considering replying to DHCPINFORMs
> with option 252 with a newline to induce
> clients to stop asking.
> Anyone doing this on a large scale, i.e.
> while trying to serve all sorts of clients?
> In theory, something could break.
> What I anticipate doing (globally):
>
> option msft-wpad code 252 = text;
> if substring (option vendor-class-identifier, 0, 8) = "MSFT 5.0" {
> option msft-wpad "\n";
> }
We do this on all of our normal DHCP servers to quell useless DHCPINFORM
chatter by Microsoft devices, with good results:
# add option sequence for suppressing DHCPINFORM
# Client browsers typically looking for wpad proxy sites
option wpad code 252 = text;
option wpad "\n\000";
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 = null, which will
# send the option at DHCPDISCOVER/DHCPREQUEST time, and will also
# suppress the DHCPINFORMS! They seem to cache it.
option dhcp-parameter-request-list = concat(option dhcp-parameter-request-list, fc);
}
________________________________________________________________________
Jay Ford, Network Engineering Group, Information Technology Services
University of Iowa, Iowa City, IA 52242
email: jay-ford at uiowa.edu, phone: 319-335-5555, fax: 319-335-2951
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