Subject: [Gen-art] Gen-ART review of draft-ietf-softwire-dslite-deployment-06

From: "Black, David" <[email-masked]>
Date: Mon, 15 Oct 2012 19:10:27 -0400

I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at
<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-softwire-dslite-deployment-06
Reviewer: David L. Black
Review Date: October 15, 2012
IETF LC End Date: October 16, 2012
IESG Telechat Date: October 25, 2012

Summary:

This draft is on the right track but has open issues, described in the review.

This is a generally well-written draft that expands considerably on the brief
deployment considerations for DS-Lite in Appendix A of RFC 6333.  The draft
is clear and reasonably well-written, and a significant improvement on that
RFC 6333 Appendix, although an understanding of RFC 6333 is necessary to
understand this draft, which seems completely reasonable.

The B4 and AFTR acronyms are clever - kudos to whomever came up with those.

I found five open issues, all of which are minor.

Minor Issues:

[1] Ironically, the first issue is that something should be said about
the relationship of this draft to Appendix A of RFC 6333.  It probably
suffices to say that this draft expands on the material in that Appendix,
as I see no need to specify that this draft updates RFC 6333 solely to
change non-normative material in an Appendix.

[2] The MTU increase technique in Section 2.2 is a "may", which is
consistent with Section 5.3 of RFC 6333.  OTOH, Section 2.2 of this
draft should also discuss the AFTR resource exhaustion concern that
described in Section 6.3 of RFC 6333, as that is a potential
operational reason for an ISP to increase MTU size (e.g., if customer
sourcing of large IPv4 packets is not sufficiently rare).

[3] Section 2.7 refers to "the AFTR's internal interface".  There may be
two internal interfaces, the physical IPv6 interface (outer header) and
the tunnel's IPv4 interface (inner header).  The text should be clarified
to indicate which interface is involved - it appears that the AFTR's
physical IPv6 interface is intended in this section.

[4] Section 2.7 cites RFC 6333 for use of DHCPv6 with DS-Lite.  RFC 6334
should be cited - either in addition to or instead of RFC 6333.

[5] Section 2.8 discusses IPv4 accounting at the AFTR, but notes that
"the AFTR does not have detailed customer identity information."  Does
that create a theft of service possibility?  If so, that possibility
should be mentioned as a security consideration.  Also, Section 2.8
ought to be expanded with a sentence or two explaining why the AFTR
does not have that identity information, and in particular to explain
whether and why it is unreasonable in some or all cases to expect
that customer identity information be provided to the AFTR as part
of provisioning each customer's softwire.

Nits:

Section 2.3 on MTU Considerations could usefully mention MTU discovery
techniques, as possibilities for customer IPv4 traffic to adapt to a
smaller IPv4 MTU.  If this is done, it would be useful to mention
RFC 4821 in addition to the mention of RFC 1191 in RFC 6333.

Section 2.4 should define "lawful intercept".  It would be helpful to
cite a reference for this concept if something appropriate can be found.

Section 2.5:
- Are one or both types of logging recommended?
- Last paragraph on p.4, "timestamped log" is not a good verb phrase.
	"maintain a timestamped log of" would be a better replacement.
- Last paragraph in section, where is the batch file sent?

In Section 2.7, I'm having a hard time understanding which traffic is
intended to be subject to the Outgoing Policies and the Incoming Policies.
Expanding each of those two bullets to explain what traffic is subject
to each class of policies would help.

Section 3.2.2.2 uses 192.0.0.2/32 as an example IP address for the
B4.  That section should also cross-reference Section 5.7 on RFC 6333
on IP address assignment to B4s, as other IP addresses may be used.

idnits 2.12.13 found a tiny nit - draft-ietf-pcp-base is now at
version 28.

Thanks,
--David
----------------------------------------------------
David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
----------------------------------------------------

---

From: "Lee, Yiu" <[email-masked]>
Date: Thu, 18 Oct 2012 00:46:24 +0000

Hi David,

Thanks very much for review the draft. Comments inline.

Thanks,
Yiu

>change non-normative material in an Appendix.

[YL] In "Overview", we will add:

"This document expands Appendix A of RFC6333 and discusses various
DS-Lite deployment considerations for operators."

>sourcing of large IPv4 packets is not sufficiently rare).

[YL] In 2.2, we will add:

"Note that reassembly at Tunnel Exit-Point is resource
	intensive. A large number of B4 may terminate on the same AFTR. If many B4
	fragment the packets, it would increase sufficient load to the AFTR for
	reassembly. We recommend the operator should increase the MTU size of the
IPv6
	network between B4 and AFTR to avoid fragmentation."

>physical IPv6 interface is intended in this section.

[YL] We replace "internal" to "IPv6"

>should be cited - either in addition to or instead of RFC 6333.

[YL] Fixed

>of provisioning each customer's softwire.

[YL] Good catch. Actually I believe AFTR "does" have both IPv4 and IPv6 to
identify the customer. I suggest we remove

"but it will potentially introduce some additional complexity because
   the AFTR does not have detailed customer identity information."

>RFC 4821 in addition to the mention of RFC 1191 in RFC 6333.

[YL] We would consider RFC 4821. However, the challenge is I don't have
information how many current OS support RFC 4821. Since DS-lite is a
transition technology, it would be unreasonable to ask the OS company to
implement RFC 4821 for DS-lite.

>cite a reference for this concept if something appropriate can be found.

[YL] We will find whether there is any reference to this concept. If we
can't find any, we would add an explanation in the draft.

>- Are one or both types of logging recommended?

[YL] We tempted to recommend source-specific log. However, some regulators
require to use both and the regulations vary country from country, this is
why we left it open and let the operators to decide.

>	"maintain a timestamped log of" would be a better replacement.

[YL] Fixed

>- Last paragraph in section, where is the batch file sent?

[YL] We will add:

"The files may be compressed before transferring to a repository server
	to better utilize bandwidth and storage."

>to each class of policies would help.

[YL] Does this help?

Outgoing Policies apply to packets originating from B4 to IPv4 network.
Incoming Policies apply to packets originating from IPv4 network to B4.

>on IP address assignment to B4s, as other IP addresses may be used.

[YL] Added the cite.

>idnits 2.12.13 found a tiny nit - draft-ietf-pcp-base is now at

[YL] Fixed.

---

From: "Black, David" <[email-masked]>
Date: Wed, 17 Oct 2012 21:11:51 -0400

Yiu,

Thank you for your responses - most of them look fine, and in 
particular anything that I don't comment on here is acceptable to me.

> 	reassembly. We recommend the operator should increase the MTU size of the IPv6

I would change "is" to "may be" in the first line.

>    the AFTR does not have detailed customer identity information."

That's definitely an easy way to address that issue, and it's fine with me.

> implement RFC 4821 for DS-lite.

That's ok - this was a nit.

> why we left it open and let the operators to decide.

Please add a version of your explanation to the draft.

> Incoming Policies apply to packets originating from IPv4 network to B4.

Yes, that's clearer, although the B4 is not the network endpoint for any
of that traffic.  I suggest:

Outgoing Policies apply to packets originating from behind the B4 with 
a destination on the IPv4 network.

Incoming Policies apply to packets originating from the IPv4 network to
a destination behind the B4.

Thanks,
--David

> -----Original Message-----
> From: Lee, Yiu [mailto:[email-masked]]
> Sent: Wednesday, October 17, 2012 8:46 PM
> To: Black, David; [email-masked]; [email-masked];
> [email-masked]; [email-masked]; [email-masked]
> Cc: [email-masked]; [email-masked]; Ralph Droms
> Subject: Re: Gen-ART review of draft-ietf-softwire-dslite-deployment-06
> 
> Hi David,
> 
> 	reassembly. We recommend the operator should increase the MTU size of the IPv6

---

From: Maglione Roberta <[email-masked]>
Date: Thu, 18 Oct 2012 09:12:29 +0200

Hello Yiu and David,

>    the AFTR does not have detailed customer identity information."

The point related to the accounting is different: what I meant here with accounting is RADIUS based accounting, commonly used in Broadband networks.

Today RADIUS accounting is done at the BNG level, the problem with the introduction of the AFTR is that the AFTR does not interact with AAA/RADIUS Server for the initial authentication/authorization/accounting phase because the authentication/authorization/accounting process happens between BNG and RADIUS Server when the session comes up.
The ATFR is not able to perform RADIUS accounting because as it does not interact with the RADIUS Server it does not have " detailed customer identity information" for example it does know the accounting session ID associated to that session, that's why it cannot do detailed accounting for each single subscriber even if the ATFR can still correlated IPv6 and IPv4 traffic belonging to the same user.

This is an important operational issue, I would suggest to keep this concept. If you think is needed I can add some lines of text in order to clarify this point.

Thanks
Regards,
Roberta
-----Original Message-----
From: Black, David [mailto:[email-masked]]
Sent: Thursday, October 18, 2012 3:12 AM
To: Lee, Yiu; Maglione Roberta; [email-masked]; [email-masked]; [email-masked]; [email-masked]
Cc: [email-masked]; [email-masked]; Ralph Droms; Black, David
Subject: RE: Gen-ART review of draft-ietf-softwire-dslite-deployment-06

Yiu,

Thanks,
--David

> >idnits 2.12.13 found a tiny nit - draft-ietf-pcp-base is now at

Questo messaggio e i suoi allegati sono indirizzati esclusivamente alle persone indicate. La diffusione, copia o qualsiasi altra azione derivante dalla conoscenza di queste informazioni sono rigorosamente vietate. Qualora abbiate ricevuto questo documento per errore siete cortesemente pregati di darne immediata comunicazione al mittente e di provvedere alla sua distruzione, Grazie.

This e-mail and any attachments is confidential and may contain privileged information intended for the addressee(s) only. Dissemination, copying, printing or use by anybody else is unauthorised. If you are not the intended recipient, please delete this message and any attachments and advise the sender by return e-mail, Thanks.

---

From: Maglione Roberta <[email-masked]>
Date: Thu, 18 Oct 2012 09:18:00 +0200

Hello Yiu and David,
regarding point 5:

> [YL] Good catch. Actually I believe AFTR "does" have both IPv4 and
> IPv6 to identify the customer. I suggest we remove
>

Thanks
Regards,
Roberta

-----Original Message-----
From: Black, David [mailto:[email-masked]]
Sent: Thursday, October 18, 2012 3:12 AM
To: Lee, Yiu; Maglione Roberta; [email-masked]; [email-masked]; [email-masked]; [email-masked]
Cc: [email-masked]; [email-masked]; Ralph Droms; Black, David
Subject: RE: Gen-ART review of draft-ietf-softwire-dslite-deployment-06

Yiu,

Thanks,
--David

---

From: "Lee, Yiu" <[email-masked]>
Date: Thu, 18 Oct 2012 12:29:09 +0000

Thanks David! I will apply your changes to the next version.

---

From: "Black, David" <[email-masked]>
Date: Thu, 18 Oct 2012 11:10:56 -0400

Hello Roberta,

In that case, more text is needed to explain in Section 2.8, and
the related theft of service concern also needs to be discussed in
that section and/or the Security Considerations section.

Thanks,
--David

> From: Maglione Roberta [mailto:[email-masked]]
> Sent: Thursday, October 18, 2012 3:18 AM
> To: Black, David; Lee, Yiu; 'draft-ietf-softwire-dslite-
> [email-masked]'
> Cc: Ralph Droms; [email-masked]; [email-masked]
> The point related to the accounting is different: what I meant here with
> accounting is RADIUS based accounting, commonly used in Broadband networks.
> 
> Today RADIUS accounting is done at the BNG level, the problem with the
> introduction of the AFTR is that the AFTR does not interact with AAA/RADIUS
> Server for the initial authentication/authorization/accounting phase because
> the authentication/authorization/accounting process happens between BNG and
> RADIUS Server when the session comes up.
> The ATFR is not able to perform RADIUS accounting because as it does not
> interact with the RADIUS Server it does not have " detailed customer identity
> information" for example it does know the accounting session ID associated to
> that session, that's why it cannot do detailed accounting for each single
> subscriber even if the ATFR can still correlated IPv6 and IPv4 traffic
> belonging to the same user.
> 
> This is an important operational issue, I would suggest to keep this concept.
> If you think is needed I can add some lines of text in order to clarify this
> point.
> 
> Thanks
> Regards,
> Roberta
> 
> To: Lee, Yiu; Maglione Roberta; [email-masked];
> Questo messaggio e i suoi allegati sono indirizzati esclusivamente alle
> persone indicate. La diffusione, copia o qualsiasi altra azione derivante
> dalla conoscenza di queste informazioni sono rigorosamente vietate. Qualora
> abbiate ricevuto questo documento per errore siete cortesemente pregati di
> darne immediata comunicazione al mittente e di provvedere alla sua
> distruzione, Grazie.
> 
> This e-mail and any attachments is confidential and may contain privileged
> information intended for the addressee(s) only. Dissemination, copying,
> printing or use by anybody else is unauthorised. If you are not the intended
> recipient, please delete this message and any attachments and advise the
> sender by return e-mail, Thanks.
>

---

From: "Lee, Yiu" <[email-masked]>
Date: Mon, 22 Oct 2012 19:48:26 +0000

Hi David,

Since the BNG would verify the v6 packets sent by B4 and the AFTR would
NAT the RFC1918 source address to the public address, I try to find a use
case where a theft could steal the service. From the AFTR's perspective,
the IPv4 address of the host behind B4 is irrelevant. Could you help to
find a use case which will introduce security risk because the AFTR can't
identify the IPv4 address?

Thanks,
Yiu

On 10/18/12 11:10 AM, "Black, David" <[email-masked]> wrote:

>> >       intensive. A large number of B4 may terminate on the same AFTR.
>>If
>> many B4
>> >       fragment the packets, it would increase sufficient load to the
>>AFTR
>> for
>> >       reassembly. We recommend the operator should increase the MTU
>>size of
>> the IPv6
>>IPv6 to
>> > >This draft is on the right track but has open issues, described in
>>the
>> > >review.
>> > >
>> > >This is a generally well-written draft that expands considerably on
>>the
>> brief
>> >       intensive. A large number of B4 may terminate on the same AFTR.
>>If
>> many B4
>> >       fragment the packets, it would increase sufficient load to the
>>AFTR
>> for
>> >       reassembly. We recommend the operator should increase the MTU
>>size of
>> the IPv6
>>IPv6 to

---

From: "Black, David" <[email-masked]>
Date: Mon, 22 Oct 2012 16:45:10 -0400

Hi Yiu,

> case where a theft could steal the service.

Important clarification - I did not originally assert that there is a
theft of service possibility, rather I only asked whether there is one -
"Does that create a theft of service possibility?".

If the answer is "no", then an explanation of why that is the answer
ought to suffice.  Here's the draft's text on this topic:

   Alternatively, AFTR is a logical place to perform IPv4 accounting,
   but it will potentially introduce some additional complexity because
   the AFTR does not have detailed customer identity information.  The
   accounting process at the AFTR is only necessary if the operator
   requires separating per user accounting records for IPv4 and IPv6
   traffic.

Continuing:

> From the AFTR's perspective,

In revising the draft, please also explain how "the operator requires
separating per user accounting records for IPv4 and IPv6 traffic" is
consistent with "the IPv4 address of the host behind the B4 is irrelevant".
The answer probably starts with an explanation of the behavior of the
NAT in the AFTR, although I note that section 2.13 of the draft describes
a case in which the IPv4 address behind the B4 appears to be relevant
(e.g., for an operator who charges differently for traffic inbound to
a customer server by comparison to other customer traffic).

Backing out of this level of detail, all I'm asking for is an explanation
of why or under what circumstances the lack of identity information at
the AFTR does not pose a security concern when usage accounting is done
there and the assumptions on which that is based - e.g., it might be
appropriate to say that the BNG should verify the v6 packets sent by B4.

I'm not trying to be difficult.  In general, absence of identity information
raises theft of service concerns in accounting systems, and if that's really
not a problem in this case, I just want to see a solid explanation of why
that's not a problem.

Thanks,
--David

> Sent: Monday, October 22, 2012 3:48 PM
> To: Black, David; Maglione Roberta; 'draft-ietf-softwire-dslite-

---

From: "Lee, Yiu" <[email-masked]>
Date: Mon, 22 Oct 2012 21:54:06 +0000

Hi David,

Got it. We will capture all these comments in the next revision.

Thanks again for reviewing the draft.

Yiu

On 10/22/12 4:45 PM, "Black, David" <[email-masked]> wrote:

>> >> That's definitely an easy way to address that issue, and it's fine
>>with
>> >>me.
>> >>
>> >> > transition technology, it would be unreasonable to ask the OS
>>company
>> >>to
>> >> > >is clear and reasonably well-written, and a significant
>>improvement
>> >>on that
>> >> > >The B4 and AFTR acronyms are clever - kudos to whomever came up
>>with
>> >> > >those.
>> >> > >
>> >> > >as I see no need to specify that this draft updates RFC 6333
>>solely
>> >>to
>> >> > >two internal interfaces, the physical IPv6 interface (outer
>>header)
>> >>and
>> >> > >[4] Section 2.7 cites RFC 6333 for use of DHCPv6 with DS-Lite.
>>RFC
>> >>6334
>> >> > transition technology, it would be unreasonable to ask the OS
>>company
>> >>to
>> >> > [YL] We will find whether there is any reference to this concept.
>>If
>> >>we
>> >> abbiate ricevuto questo documento per errore siete cortesemente
>>pregati
>> >>di