Re: Last Call: <draft-arkko-ipv6-transition-guidelines-08.txt> (Guidelines for Using IPv6 Transition Mechanisms during IPv6 Deployment) to Informational RFC

[<[e-mail]>]

Dear all,

Please find below some comments about this I-D.

(1)

* Precise in the introduction section the type of networks which are concerned with the IPv6 deployment models listed in the I-D; in particular mention that both corporate networks and providers networks are concerned.

* Fixed and mobile networks may adopt distinct IPv6 deployment strategies because of the differences between the two networks (e.g., controlled CPE vs. non controlled handsets).

* It seems services infrastructures (e.g., VoIP, IP TV) are out of scope. This should be mentioned. Note that some service-related discussed is covered in Section 4.4.

(2)

Page 5/6, the I-D says:


  " o  The ability to offer a valuable service.  In the case of the
      Internet, connectivity has been this service.

   o  The ability to deploy the solution in an incremental fashion.

   o  Simplicity.  This has been a key factor in making it possible for
      all types of devices to support the Internet protocols.

   o  Openly available implementations.  These make it easier for
      researchers, start-ups and others to build on or improve existing
      components.

   o  The ability to scale.  The IPv4 Internet grew far larger than its
      original designers had anticipated, and scaling limits only became
      apparent 20-30 years later.

   o  The design supports robust interoperability rather than mere
      correctness.  This is important in order to ensure that the
      solution works in different circumstances and in an imperfectly
      controlled world."

and in Page 6: "These factors are also important when choosing IPv6 migration tools.", but:

* The I-D does not show how these factors are applied for the tools listed in the I-D; a table with a set of criteria would be useful;

* The first criterion is IMHO meaningless for IPv6 deployment because IPv6 does not offer a new service compared to IPv4.

* I'm not sure that having an open source for a given tool can be an argument to RECOMMEND or NOT a given tool;

* How "scalability" is defined (5th bullet)?? All the solutions listed in the I-D need a NAT (l2-nat, ds-lite nat44, nat44, nat64), to what extent a CGN is considered as a scalable solution?

* The last bullet is not clear: Do you consider that DS-Lite satisfies this factor? FWIW, DS-Lite has been rejected by the 3GPP because it requires specific functions on the UE.

(3)

>From the perspective of transitioning networks to IPv6, I don't see the rationale behind including techniques such as those listed in "4.2. Crossing IPv4 Islands" as a candidate solutions for IPv6 deployment. This section can be removed to an appendix.

(4)

(a) I have an issue with the following statements in the I-D:

On page 6, the ID states:  "The third scenario is more advanced and looks at a service provider network that runs only on IPv6 but which is still capable of providing both IPv6 and IPv4 services."

and in page 11, the ID mentions:

"   The recommended tool for this model is Dual Stack Lite
   [I-D.ietf-softwire-dual-stack-lite<http://tools.ietf.org/html/draft-arkko-ipv6-transition-guidelines-13#ref-I-D.ietf-softwire-dual-stack-lite>].  Dual Stack Lite provides both
   relief for IPv4 address shortage and makes forward progress on IPv6
   deployment, by moving service provider networks and IPv4 traffic over
   IPv6.  Given this IPv6 connectivity, as a side-effect it becomes easy
   to provide IPv6 connectivity all the way to the end users."

Taking into account the current DS-Lite specification, this recommendation is not justified for the following reasons:

* For Ds-Lite technique to be deployed in a IPv6-only realm, and as currently specified in DS-Lite specification, this would mean that DS-Lite AFTR(s) are to be located at the boundaries of the IPv6-only domain.

* This design choice would lead to non optimal intra-domain paths to place communications between two DS-Lite serviced customers.

* This centralised model is not suitable for service providers who want to deploy DS-Lite AFTRs closer to the customers.


(b) The I-D states in page 11: "Given this IPv6 connectivity, as a side-effect it becomes easy to provide IPv6 connectivity all the way to the end users."

This wording is not accurate; IPv6 connectivity is not a side-effect of DS-lite but rather a pre-requisite for DS-Lite (e.g., DHCPv6 is required to configure for instance the AFTR NAME option, dual-stack CPE, etc.).

(5)

* In Section "4.4. IPv6-only Deployment", add a sentence to precise that the issues listed in [I-D.ietf-intarea-shared-addressing-issues<http://tools.ietf.org/html/draft-arkko-ipv6-transition-guidelines-13#ref-I-D.ietf-intarea-shared-addressing-issues>] are still valid when NAT64 is deployed.

* Page 13, change "SIP (Session Identity Protocol)" to "SIP (Session Initiation Protocol)";

* Page 13: "One might position a web proxy, a
   mail server, or a SIP (Session Identity Protocol) back-to-back user
   agent across the boundary between IPv4 and IPv6 domains, so that the
   application terminates IPv4 sessions on one side and IPv6 sessions on
   the other.  Doing this preserves the end-to-end nature of
   communications between gateways.  For obvious reasons, this solution
   is preferable to the implementation of Application Layer Gateways in
   network layer translators.
"

(a) Why only listing the back-to-back user agent option (this option is valid)? Why not deploying means for NAT traversal is not listed as an alternative?

(b) "Doing this preserves the end-to-end nature of communications between gateways": Which gateways?

(c) For the SIP case, still there is a need for a translator for media flows;

(d) Service-related discussions are not elaborated in other sections: I would prefer to have a similar discussion for the DS model, in particular issues in SIP environments to signal both IPv4 and IPv6 addresses in the SDP offers; means to prioritise the use of IPv6; how the SIP Proxy Server can determine whether there is a need to invoke a SIP ALG/NAT64/NAT46 (e.g.., translator should be avoided when a DS UA calls a IPvx-only/DS UA. ALG/NAT46/NAT64 should be invoked only for IPvx-IPvy sessions), etc.

* Add a reference to http://tools.ietf.org/html/draft-ietf-v6ops-v6-in-mobile-networks-02

(6)

It would be valuable if the I-D describes some migration paths and examples about the use of the tools listed in the I-D; e.g.,:

* How DS-Lite CGN devices can be removed from the network since it is supposed to be a transition solution. This would be a good example to apply what is stated in the I-D in page 5: "The end goal is network-wide native IPv6 deployment, resulting in the
   obsolescence of transitional mechanisms based on encapsulation,
   tunnels, or translation, and also resulting in the obsolescence of
   IPv4."

* How to encourage the use of native IPv6 transfer capabilities: address selection issues, application considerations, etc.

Cheers,
Med

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