Subject: [dhcwg] Re: Free Options

From: Ralph Droms <[email-masked]>
Date: Thu, 10 Jan 2008 11:08:21 -0500

Ruben - Take a look at RFC 2131, RFC 2132, RFC 3942 and http://www.iana.org/assignments/bootp-dhcp-parameters 
  for details about option codes available for private use.

Executive summary - with some exceptions, option codes 224-254 are  
available for private use.  I don't recall the details; I think the  
two option codes you mentioned are known to be in unofficial use, but  
they don't seem to be documented in http://www.iana.org/assignments/bootp-dhcp-parameters 
.  Bernie - did you receive any information about 249 and 252 in your  
followup to RFC 3942?

- Ralph Droms

On Jan 10, 2008, at Jan 10, 2008,10:43 AM, Ruben Rios wrote:

> Hi there,
> I have been searching on DHCP Options because I would like to use  
> some private ones for my own private use. Can anyone tell me which  
> of them can I use for that? I thought I could use any, but while  
> eavesdropping on my network I have realized some of these options  
> are already in use ( 249: Classless static routes; 252: proxy  
> autodiscovery). Are there any others I should avoid using?
>
> Thanks a lot!
> Rubén Ríos
>
>
>
> Web Revelación Yahoo! 2007:
> Premio Favorita del Público - ¡Vota tu preferida!

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From: "Bernie Volz (volz)" <[email-masked]>
Date: Thu, 10 Jan 2008 11:10:51 -0500

Yes, I did find (or was providing some information) about these options:

249		Windows XP clients request option 249.
252		MAC OS X clients request option 252.

But as they are outside the RFC 3942 reclassified range, there was no point in doing anything about them.

- Bernie

-----Original Message-----
From: Ralph Droms (rdroms) 
Sent: Thursday, January 10, 2008 11:08 AM
To: [email-masked]
Cc: Bernie Volz (volz); DHC WG
Subject: Re: Free Options

- Ralph Droms

---

From: Ralph Droms <[email-masked]>
Date: Thu, 10 Jan 2008 11:13:11 -0500

I wonder if it might be worth adding these as a footnote to the IANA  
page?  Did you find others in the range 224-254 that might be useful  
to record?

- Ralph

---

From: "Bernie Volz (volz)" <[email-masked]>
Date: Thu, 10 Jan 2008 11:36:37 -0500

Yes:

230-238		MAC OS X NETBOOT also uses options 230-238. See http://mike.passwall.com/macnc/analysis.html and http://www.macos.utah.edu/Documentation/NetBoot/NetBoot.html.

----

I'd perfer we NOT add these to the IANA page as that begins to make them look like they are assigned for this use.

- Bernie 

-----Original Message-----
From: Ralph Droms (rdroms) 
Sent: Thursday, January 10, 2008 11:13 AM
To: Bernie Volz (volz)
Cc: [email-masked]; DHC WG
Subject: Re: Free Options

- Ralph

---

From: "David W. Hankins" <[email-masked]>
Date: Thu, 10 Jan 2008 10:21:36 -0800

I'm vaguely unfamiliar with vendor-use of 249 (I recall it, but I
can't remember why), but 252 I recognize as being used by WPAD;

  http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol
  http://www.ietf.org/proceedings/99nov/I-D/draft-ietf-wrec-wpad-01.txt

MAC OSX is indeed nice enough to put this on their PRL; Windows (as of
95 I think?) will DHCPINFORM multiple times expecting to find WPAD in
the reply, without putting it in the PRL, and will continue to
retransmit if it's absent.  If you throw 252 in there, it will only
DHCPINFORM once, and (if you search the archive of the dhcp-users
mailing list) you'll see someone who tried this got hits on the proxy
they named which indicated they were from "Microsoft Industry
Updater."  So it sounds like Windows' automatic updates use WPAD to
locate a proxy to load updates from.

It also appears that if you provide this option in normal Request/Acks
that other software, such as IE and Firefox, will find and use its
contents.

I believe the reason it appears in Mac OSX's PRL is because Safari
will use it.

Ruben;

You can use whatever option codes you want from 224 to 254 inclusive,
including options 249 and 252.  Collissions within the site-local
space was one of the things Ted prepared for when he originally wrote
the software; you can manage collisions in ISC DHCP by using 'site
local spaces'.  Documentation for these can be found in the dhcpd.conf
manpage, but here's a brief primer;

	option space vendor1;
	option vendor1.blart code 252 = text;

	option space vendor2;
	option vendor2.frobnitz code 252 = array of ip address;

	class "vendor1s" {
		match if option vendor-class-identifier = "vendor1";

		site-local-space "vendor1";

		# vendor1s do not put 252 on their PRL!
		option dhcp-parameter-request-list =
			concat(option dhcp-parameter-request-list, FC);
	}

	class "vendor2s" {
		match if option vendor-class-identifier = "vendor2";

		site-local-space "vendor2";
	}

	option vendor1.blart "http://global.example.com/your.pac";
	option vendor2.frobnitz global.example.com;

	subnet yadda yadda {
		option vendor1.blart "http://local.example.com/your.pac";
	}

In this example, the vendor-class-identifier provided by the client
(check wireshark or vendor documentation to find out what these really
say) is used to assign the client a site-local-space.  When the
reply packet is transmitted, options within the "site local" range are
tried first from the named site local space.  So vendor1's will use
the vendor1.blart values, and vendor2's are given theirs.

This gives you a way to make sense of varying, different views of
the site-local option space.

3.1.0 and later differ from 3.0.x maintenance track; in 3.1.0 we
changed the site-local cutoff to 224 to track RFC 3942, but forgot to
put in a warning for configs using options prior to 224.  We're going
to put in a warning in 3.1.1, and since we're bothering to detect
options between 128-224, we're supporting them as well (3.1.0 won't
"find" options between 128-224 in site-local spaces).

-- 
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?	 https://secure.isc.org/store/t-shirt/
-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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From: "David W. Hankins" <[email-masked]>
Date: Thu, 10 Jan 2008 10:31:02 -0800

On Thu, Jan 10, 2008 at 11:36:37AM -0500, Bernie Volz (volz) wrote:
> I'd perfer we NOT add these to the IANA page as that begins to make
> them look like they are assigned for this use.

I agree with the statement that we avoid discussion of these options
as part of RFC 3942 work.

But I think at least option 252 is in widespread use and is very
poorly documenting (bordering upon secrecy).  I think it would be in
the public's best interest for 252 to be documented and allocated
formally, and I've been meaning to volunteer to do so.

In my copious spare time.

But, I meant to do that long before RFC 3942, and still think of it
as a separate issue.

We should more or less evaluate this on a case by case basis.