Re: [dhcwg] Comments on draft-ietf-dhc-dhcpv6-opt-netboot-05

[Thomas Huth <THUTH at de.ibm.com>]

Damien Neil wrote on 06/10/2009 22:03:45:

> I think that ordering of options should not be significant, although
> I'm not convinced that non-significant ordering is sufficient reason
> to use multiple instances of an option.
>
> One of my concerns is the complexity of presenting option data to a
> user--to a server administrator specifying what to send to a client,
> or to a network configuration script executed by a client.
>
> With DHCPv4 single-instance options, you can say "the value of option
> <foo> is <bar>".  For example, in ISC dhcpd:
>
>    option domain-name-servers = 10.0.0.1, 10.0.0.2;
>
> When you introduce multiple-instance options, this becomes more
> complicated.  There are various means of presenting this to the user,
> but I don't find any of them truly satisfactory.

From a user point of view (I am only a user of dhcp servers, never wrote
one on my own), I would be fine with specifying multiple "option boot-url
= ..." lines in the configuration file. Please excuse my ignorance, but I
can't see a real problem with this, so I'd like to know what are your exact
concerns about this?

> I note that ISC dhcpd doesn't appear to support defining multiple
> instances of an option at this time.  The dhcp-options(5) manpage
> states, "normally [multiply-instanced options] are options which are
> digested by the DHCP protocol software, and not by users or
> applications."  (If I'm wrong about this, and such support does exist
> in ISC dhcpd, my apologies.)
>
> I'm not absolutely opposed to multiply-instanced options, but I do
> think there's more implementation complexity to them than may first
> meet the eye.

Well, according to the RFC 3315:

"Unless otherwise noted, each option may appear only in the options
 area of a DHCP message and may appear only once.  If an option does
 appear multiple times, each instance is considered separate and the
 data areas of the options MUST NOT be concatenated or otherwise
 combined."

For me, that sounds like multiple-instance options are allowed if there is
a reason for using them. So I think your dhcp server should somehow support
that in its configuration file, too...?


Mit freundlichen Grüßen / Kind regards,
   Thomas Huth
                                                                       
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