Re: [v6ops] [dhcwg] Fwd: New Version Notification for draft-link-dhc-v6only-01.txt

[<[e-mail]>]

Hi Jen,

Thank you for sharing this updated version. Below some points that I do think need more clarification in the I-D: 

(1) The document is too NAT64 centric. The proposal may apply as well for other IPv6-only deployment scenarios (typically, unmanaged IPv6-only CPEs with IPv4aaS).

(2) A discussion on the benefit of this extra signal compared to relying on existing signals (pref64, aftr_name, map_container...). For example, a host that supports the option is ready to wait at minimum 300s and disable its IPv4 configuration regardless of what is happening on the IPv6 leg. How is that superior to a host delaying DHCP process by xxx ms should be explained further.  

(3) How "IPv6-only preferred" mode is supposed to be set at the host side:

==
   A DHCP client SHOULD allow a device administrator to configure
   IPv6-only preferred mode either for a specific interface (to indicate
   that the device is IPv6-only capable if connected to a NAT64 network
   via that interface) or for all interfaces.  
==

* I guess the default value when the option is supported by a host is to disable including it in the request. The document should include a discussion on the default behavior. 
* If an explicit action is needed from the user to enable including the option, having a discussion to what extent the feature is likely to be enabled would be needed.

(4) The document is still mixing the DHCP client vs. host behaviors. For example, 

   Clients not capable of operating in an IPv6-only NAT64 environment
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   MUST NOT include the IPv6-only Preferred option in the Parameter
   Request List of any DHCP packets and MUST ignore that option in
   packets received from DHCP servers.

does not make sense for a DHCP client. 

Also, how the host is able to assess/determine that it is (not) capable to behave in the IPv6 mode? 

(5) The definition of IPv4aaS is not aligned with other RFCs: e.g., RFC8585 says the following: 

   "IPv4aaS" stands for "IPv4-as-a-Service", meaning transition
   technologies for delivering IPv4 in IPv6-only connectivity.

While yours is: 

   IPv4-as-a-Service: a deployment scenario when end hosts are expected
   to operate in IPv6-only mode by default and IPv4 addresses can be
   assigned to some hosts if those hosts explicitly opt-in to receiving
   IPv4 addresses.

(6) Do you consider a host with CLAT function as an IPv6-only host?

If so, the following definition should be updated to refer to "IPv4 connectivity" rather than "IPv4" in general. This is because an IPv4 address is required for CLAT for example.

==
   IPv6-only capable host: a host which does not require IPv4 and can
   operate on IPv6-only networks.
==

(7) Wouldn't the following add an extra delay for applications requiring CLAT?

==
The host MAY disable IPv4 stack
   completely for V6ONLY_WAIT seconds or until the network disconnection
   event happens.
==

(8) Consider returning an address from the range defined in RFC7335 for IPv6-only hosts. Such IPv4 addresses are required anyway for some IPv6-only hosts (those with a CLAT for example).

====
   The result is that 192.0.0.0/29 may be used in any system
   that requires IPv4 addresses for backward compatibility with IPv4
   communications in an IPv6-only network but does not emit IPv4 packets
   "on the wire".
====

Cheers,
Med

> -----Message d'origine-----
> De : dhcwg [mailto:[e-mail]] De la part de Jen Linkova
> Envoyé : mardi 10 décembre 2019 01:02
> À : [e-mail]
> Cc : V6 Ops List
> Objet : [dhcwg] Fwd: New Version Notification for draft-link-dhc-v6only-
> 01.txt
> 
> Hello,
> 
> Thanks to everyone for very productive centi-thread on
> draft-link-dhc-v6only-00 ;)
> Here is the improved version, -01.
> 
> The main changes:
> 
> - The option is not zero length anymore. It has 4-bytes value which
> might contain V6ONLY_WAIT timer. Benefits:
>     --- allows the network administrators to pilot the changes and
> rollback quickly if needed;
>     --- addressed some concern about an option having zero length
> (allegedly it might confuse some clients)
> 
> - Using a dedicated address to return to clients is now an optional
> optimisation. By default the server is expected just to return a
> random address (as usual).
> 
> - Typos fixed (probably some new typos added though).
> 
> The authors would like the DHC WG to consider adopting this document.
> 
> Thank you!
> 
> ---------- Forwarded message ---------
> From: <[e-mail]>
> Date: Tue, Dec 10, 2019 at 10:44 AM
> Subject: New Version Notification for draft-link-dhc-v6only-01.txt
> To: Tomek Mrugalski <[e-mail]>, Lorenzo Colitti
> <[e-mail]>, Jen Linkova <[e-mail]>, Michael C.
> Richardson <[e-mail]>
> 
> 
> 
> A new version of I-D, draft-link-dhc-v6only-01.txt
> has been successfully submitted by Jen Linkova and posted to the
> IETF repository.
> 
> Name:           draft-link-dhc-v6only
> Revision:       01
> Title:          IPv6-Only-Preferred Option for DHCP
> Document date:  2019-12-09
> Group:          Individual Submission
> Pages:          10
> URL:
> https://www.ietf.org/internet-drafts/draft-link-dhc-v6only-01.txt
> Status:         https://datatracker.ietf.org/doc/draft-link-dhc-v6only/
> Htmlized:       https://tools.ietf.org/html/draft-link-dhc-v6only-01
> Htmlized:       https://datatracker.ietf.org/doc/html/draft-link-dhc-v6only
> Diff:           https://www.ietf.org/rfcdiff?url2=draft-link-dhc-v6only-01
> 
> Abstract:
>    This document specifies a DHCP option to indicate that a host
>    supports an IPv6-only mode and willing to forgo obtaining an IPv4
>    address if the network provides IPv6 connectivity.
> 
> 
> 
> 
> Please note that it may take a couple of minutes from the time of
> submission
> until the htmlized version and diff are available at tools.ietf.org.
> 
> The IETF Secretariat
> 
> 
> --
> SY, Jen Linkova aka Furry
> 
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