[Dnsmasq-discuss] Proposal for DHCP Option 93 capture

richardvoigt at gmail.com richardvoigt at gmail.com
Fri Dec 26 15:17:59 GMT 2008


On Fri, Dec 26, 2008 at 8:39 AM, Joey Korkames <joey+lists at kidfixit.com> wrote:
>>>
>>> Maybe the option could work like dhcp-vendorclass does now for recieved
>>> vendor identifier strings, allowing you to reclass special machine types to
>>> their own bootfiles/servers:
>>>
>>> dhcp-arch=peecees,00:00 #x86-32
>>> dhcp-arch=itanics,00:02 #IA64
>>> dhcp-arch=hammers,00:06 #x86-64
>>> dhcp-arch=mactels,00:07 #EFI x86-64
>>>
>>
>> My first thought was that it might be better, rather than adding yet
>> another keyword, to extend dhcp-match to match the contents of the option,
>> using the same hex-and-wildcards data representation that dhcp-mac uses.
>>
>> So your first example would become
>> dhcp-match=peecees,93,00:00
>
> I really like this idea - a custom force match for recieved options to go
> along with the existing means of forcing options to be sent back.
> This brings dnsmasq a lot of parity with ISC DHCP, minus all the crazy
> math/variable transformation functions for composing reply values.
>
>> The only fly in the ointment is that RFC4578 specifies that option 93 can
>> hold _more_than_one architecture spec, and the above syntax is not rich
>> enough to match that; to do so brings us back to a special keyword and
>> associated code.
>
> Well, one could write multiple statements (of the dhcp-match syntax) for all
> the possible variations of the option value that they can observe at their
> site (with dhcpdump). Or perhaps added support for matching against regular
> expressions. Its such an obscure (but useful) option that it may be best to
> only minimally support it until its current implementation by clients
> becomes more apparent (and fleshed out further with DHCPv6).

Rather than a regex match, I'd guess support for anchoring to the
start and/or end of the data or a constant offset would be simpler to
implement, much lower performance hit, and take care of most users.
And I guess the hex-and-wildcards takes care of the constant offset
part.

>
> -joey
>
>
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