Re: [dhcwg] WGLC for draft-ietf-dhc-dhcpv4-over-dhcpv6-03 - Respond by Dec 9, 2013

Marcin Siodelski <msiodelski@gmail.com> Wed, 27 November 2013 18:42 UTC

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Date: Wed, 27 Nov 2013 19:42:29 +0100
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From: Marcin Siodelski <msiodelski@gmail.com>
To: Simon Perreault <simon.perreault@viagenie.ca>
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Subject: Re: [dhcwg] WGLC for draft-ietf-dhc-dhcpv4-over-dhcpv6-03 - Respond by Dec 9, 2013
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On Wed, Nov 27, 2013 at 7:03 PM, Simon Perreault
<simon.perreault@viagenie.ca> wrote:
> Le 2013-11-27 11:03, Marcin Siodelski a écrit :
>
>> In the case proposed in the draft: if I want to use the multicast, I
>> send minimal amount of information to the client (boolean option).
>
>
> What if you want to use a different multicast address than the well-known
> one?

The section "4. Architecture Overview" of the draft says:
" Typically, a 4o6 DHCP client communicates with the 4o6 DHCP servers
   using well known All_DHCP_Relay_Agents_and_Servers multicast address."

Also section "8.  4o6 DHCP Client Behavior" says:
   o  If the client receives the DHCPv4-over-DHCPv6 Enable Option but no
      4o6 Servers Address Option, it SHOULD enable the DHCPv4-over-
      DHCPv6 function, and use IPv6 All_DHCP_Relay_Agents_and_Servers
      multicast address to communicate with servers and relays.

The document assumes that there is only one multicast address that the
client uses. Why would client use any other multicast address? The
All_DHCP_Servers address is rather used by relays, not clients.

>
>
>> If
>> I want to use unicast I send two options, if client receives both
>> options it uses unicast. I am not certain if this is any more
>> complicated that parsing the option, eliminate the duplicates and the
>> problem of presence of both multicast and unicast etc.
>
>
> I think that implementation-wise they're pretty much the same complexity.
> The gain would be in one less option to define, which would make the
> document shorter and easier to understand.
>

It would make a document shorter and easier in one section but would
make it longer and more complex in the other: how should client behave
receiving both unicast and multicast address, for instance? Also, it
should then give more thought to the security section.

The implementation complexity can be pretty much the same in that, you
can reuse the code which validates the unicast address list for
multicast case, yes. But it still doesn't solve the other problem
given above. Client doesn't have to check consistency of the addresses
if it receives the simple boolean-type option:
- duplicated unicast addrs
- more than one multicast
- invalid multicast
- both multicast and unicast present

If the document is unclear or ambiguous in the part that describes the
client's behavior when it receives two options, we should work to make
it clearer.

Marcin