Re: [Gen-art] Gen-ART LC review of draft-ietf-geopriv-http-location-delivery-07

["Mary Barnes" <[e-mail]>]

Hi Ben,

Thank you for your detailed review. After consulting with the
contributors, we've come up with the responses embedded below [MB].

Thanks,
Mary. 

-----Original Message-----
From: Ben Campbell [mailto:[e-mail]] 
Sent: Tuesday, May 06, 2008 5:02 PM
To: Barnes, Mary (RICH2:AR00); [e-mail];
[e-mail]; [e-mail]; General Area
Review Team
Cc: Robert Sparks; Jon Peterson; Cullen Jennings
Subject: Gen-ART LC review of
draft-ietf-geopriv-http-location-delivery-07

I have been selected as the General Area Review Team (Gen-ART) reviewer
for this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).

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


Document: draft-ietf-geopriv-http-location-delivery-07
Reviewer: Ben Campbell
Review Date:  2008-05-06
IETF LC End Date: 2008-05-07
IESG Telechat date: (if known)

Summary:

This document is almost ready for publication as a proposed standard.  
I have a few questions and comments that should be considered prior to
publication.

Comments:

-- Substantive comments:

-- I am a little bit confused by the scope of applicability of this
draft. Section 3, paragraph 1 says "This document assumes that the LIS
is present within the same administrative domain as the Device (e.g.,
the access network)." However, section A.3. claims compliance to a
requirement to the effect of "The design of the L7 LCP MUST NOT assume a
business or trust relationship between the Application Service Provider
(ASP) and the Access Network Provider." (It is possibly I am
misunderstanding what ASP means in this context?)

[MB] The ASP is defined in the RFC 5012 (ECRIT requirements that is a
normative reference for draft-ietf-geopriv-l7-lcp-ps).  The ASP is the
entity that provides voice services for example and really should be
independent of the LIS. The ASP might eventually make use of the
information that a device gets using HELD, however, the ASP is entirely
outside the scope of the HELD protocol, which I think is what that
requirement is saying.  I can see how the response to that requirement
could be misleading, so I would propose to change as follows:
OLD:
   HELD describes a location acquisition protocol and has no
   dependencies on the business or trust relationship between the ASP
   and the Access Network Provider.  Location acquisition using HELD is
   subject to the restrictions described in Section 10.
NEW:
   HELD describes a location acquisition protocol between a Device and 
   a LIS. In the context of HELD, the LIS is within the Access Network.

   Thus, HELD is independent of 
   the business or trust relationship between the Application Service 
   Provider (ASP)
   and the Access Network Provider.  Location acquisition using HELD is
   subject to the restrictions described in Section 10.
[/MB]

Furthermore, certain aspects of HELD seem to require fairly tight
coupling between the LIS and the access network. For example, the NIS
needs to know about any range of addresses for which it is likely to
have erroneous location info due to VPNs and NATs. The security
considerations indicate that the network needs to be properly configured
to avoid ip spoofing attacks, which would seem to indicate at least an
administrative coupling between the access network provider. It goes on
to make a normative statement that network configuration SHOULD be
considered.

A paragraph or two describing the expected network architecture might
clear this up. Maybe this is covered sufficiently in some of the
referenced documents?
[MB] Figure 1 was intended to show the general architectural elements
relevant to HELD. Draft-ietf-geopriv-l7-lcp-ps defines some more
specific scenarios, such as DSL, wireless, etc. But, again, these are
all independent of the Access Network to ASP interface and are only
addressing the interface between a LIS and the entity (Device in the
context of the HELD document) requesting the location.
The LIS and access network need to share a special relationship, but
attempting to enumerate the options is only likely to limit
applicability unnecessarily.
[/MB]


-- I would like to see a little more analysis on the safety of using the
source IP address as the device identifier. My instinct says that
reverse routeability may keep this from being a problem--but the
security considerations do indicate source address spoofing could cause
LI to be compromised, and add a list of approaches, "one or more" of
which is recommended to limit the exposure. If there are in fact risks
of compromise, I think the draft needs some more exhaustive and explicit
statements of what I must do to avoid such attacks.
[MB] The first bullet is actually documented as a MUST include the
"expires" parameter in the protocol section when one uses locationURIs.
So, perhaps it would resolve your concern to make that first  bullet a
MUST and rearrange this slightly, since one MUST do both the first
already and per the subsequent paragraph, the third is really only
optional in the context of a fixed network. So, I would propose
something like the following:
OLD: 
   One or more of the
   following approaches are RECOMMENDED to limit these exposures:

   o  Location URIs SHOULD have a limited lifetime, as reflected by the
      value for the expires element in Section 6.5.2.
   o  The network SHOULD have mechanisms that protect against IP address
      spoofing, such as those defined in [RFC3704].
   o  The LIS and network SHOULD be configured so that the LIS is made
      aware of Device movement within the network and addressing
      changes.  If the LIS detects a change in the network that results
      in it no longer being able to determine the location of the
      Device, then all location URIs for that Device SHOULD be
      invalidated.

   The above measures are dependent on network configuration, which
   SHOULD be considered.  For instance, in a fixed internet access,
   providers may be able to restrict the allocation of IP addresses to a
   single physical line, ensuring that spoofing is not possible; in such
   an environment, other measures may not be necessary.

NEW: 
   These exposures are limited by the following:

   o  Location URIs MUST have a limited lifetime, as reflected by the
      value for the expires element in Section 6.5.2.  The lifetime
      of location URIs necessarily depends on the nature of the access.
   o  The network SHOULD have mechanisms that protect against IP address
      spoofing, such as those defined in [RFC3704].
   o  The LIS and network SHOULD be configured so that the LIS is made
      aware of Device movement within the network and addressing
      changes.  If the LIS detects a change in the network that results
      in it no longer being able to determine the location of the
      Device, then all location URIs for that Device SHOULD be
      invalidated.

   The above measures are dependent on network configuration, which
   SHOULD be considered.  For instance, in a fixed internet access,
   providers may be able to restrict the allocation of IP addresses to a
   single physical line, ensuring that spoofing is not possible; in such
   an environment, additional measures may not be necessary.

[/MB]

-- The lbyr requirements draft includes a SHOULD level requirement that
a client should be able to cancel location references. HELD does not
seem to allow for that capability. I know it was only a SHOULD, but was
there a particular reason to leave it out?
[MB]  The pre-working group version of HELD had an explicit means to
void a 
location URI, and provided a means for the Target to set the lifetime 
of the URI. Such a mechanism requires explicit management of Target 
state on the LIS. It was decided by the WG that this wasn't necessary
for 
the base specification. There is 
one individual submission that currently addresses these
considerations but no formal approach has been adopted by the WG at this
stage. 
[/MB]

-- Section 4.2: I understand that the authz mechanisms for dereferencing
location URLs constitute a bit of an "elephant in the room". But do we
really think it is useful to punt entirely on that?  
The referenced doc does not seem all that helpful on the matter. Even an
example of a potentially useful approach might be helpful. (I realize
this is not a HELD problem per se, but without some mechanism for it, I
question the usefulness of location by reference in HELD.) (If we can
point to a location dereference protocol and claim that spec solves
this, then no problem.) 
[MB] This should be addressed in the deref-protocol document. I can add
a reference to that doc, as well, if you think it's necessary.  [/MB]

Section 4.3.1: Should there be normative advice in this section?
[MB] I'm not clear as to whether you're suggesting we should or should
not have normative text in this section. We do have normative statements
in the first paragraph, but there aren't in the second. Part of the
issue is this text was carefully crafted as a result of WG consensus,
thus it's perhaps not as strong as some would like. The language was
softened in this section during the -03 to -04 changes. The
justification was that we can't mandate behaviors on elements unless
it's specific to the actual protocol. [/MB]

Section 6.2 and 6.2.1: I don't see an obvious way to say I only want to
get location by value. Is that intentional?  
[MB] Correct. You cannot ask for just "any" location by value. You can
ask for just one type of location or both types using "exact", but you
can't do an either/or.  If you want either/or, then you may also get a
locationURI by just using "any". It makes the protocol slightly more
complicated to allow that, when it didn't seem like that would be a high
runner - e.g., if neither of the location by values were available, then
wouldn't you want to use a locationURI, so this in the end could save on
the number of requests at the cost of sometimes getting more information
than you want. [/MB]

Section 6.3, error code unsupportedMessage:

Wasn't there a normative statement ealier that the LIS MUST ignore
anything in a request that it does not understand? If so, when would
this get used?

[MB] The rationale for including this error is take care of any 
totally new messages that are introduced. The earlier statement is
actually 
a slightly different case, and refers to the 
concept of additional namespace elements being included in an existing
message. 
For example, if a locationRequest with an identity 
extension in it is sent, the LIS is free to accept the locationRequest,
but 
ignore the identity extension that it doesn't understand, and 
everything should just work. The unsupportedMessage case would be like 
the Target sending a createContext message to the LIS and the LIS
being able to send something sensible back to the Target to say I don't 
understand this. These cases are quite different, and the second case 
is actually quite catchable by most XML parsers.

This could probably be addressed by the following change : 
OLD:
unsupportedMessage:  This code indicates that an element in the XML
      document for the request, was not supported or understood by the
      LIS.

NEW:
unsupportedMessage:  This code indicates that an element in the XML
      document for the request, was not supported or understood by the
      LIS.  This error code is used when a HELD request contains a
document 
      element that is not supported by the receiver. 

And, then we should quality that earlier statement in section 5.2 as
follows:
OLD:
   The LIS MUST ignore any part of a location request message that it
   does not understand.
NEW:
   The LIS MUST ignore any part of a location request message that it
   does not understand, except the document element. 
[/MB]

6.5.2: Can you give any guidance about useful value ranges for
"expires"? I assume very short expirations would not be useful.
[MB] Correct. These should not have short expirations. We could add
something like the following at the end of that first paragraph:
NEW: 
  The "expires" parameter is RECOMMENDED not to exceed 24 hours. 
[/MB]

6.6, last paragraph:

"Note that the presence parameter is not explicitly shown in the XML
    schema Section 7 for a location response message due to XML schema
    constraints."

Is that not a problem, since section 7 is the formal definition of the
protocol syntax?
[MB] Maybe we should change this to read:
    "Note that the presence parameter is not explicitly shown in the XML
    schema Section 7 for a location response message due to XML schema
    constraints related to the PIDF namespace.  Thus, the "##other"
namespace serves 
    as a placeholder for the presence parameter in the schema."
[/MB]



Section 8:

I'm a little confused by the fact that a HELD URI can show up both in a
HELD response, and in LIS discovery. Does this use of a HELD URI imply
the use of the HELD protocol? If so, how would a HELD URI in a
locationReponse message be used? Since HELD uses the source IP address
for the identifier, it is not useful to transmit the URI to another
device, right?

[MB] The HELD URI is defined as a fairly general URI that can be used
both to provide the URI for a LIS and to provide the URI associated with
a specific location.  And, there may be other uses - the obvious one
being the dereference. The correlation of the source IP address to a
specific location URI isn't something specific to HELD - it's the LIS
that determines the location (using source IP address) and then provides
the LIS associated location URI in the response.  This document doesn't
provide a complete description of the usages of the URI (e.g.,
dereference) and it's not the intention to do so, so maybe that's the
confusion. The use of the HELD URI within this document is limited by
the functionality defined in this document, but shouldn't necessarily
limit the use of the HELD URI overall (if that makes sense). Perhaps
adding something like the following at the end of that first paragraph
would help:
NEW:
  There are other uses of the HELD: URI, such as
[I-D.winterbottom-geopriv-deref-protocol]. 
  Thus, the usages of the HELD: URI described in this document are not 
  intended to limit the applicability of the HELD: URI to other relevant
interfaces. 

[/MB]



-- Nits and Editorial Comments:

[MB] I'll fix all of these that you suggest, although, I've one question
on the next to the last one as I'm not clear as to the concern. [/MB]

S1: Expand LIS on first use. (You do so later in paragraph.)

Section 4:

Paragraph 1

I realized at this point I had not yet seen an expansion of "HELD", nor
a statement that HELD is the protocol being defined in this document
outside of the document title. Maybe an official "naming"  
sentence in the last paragraph of the intro would help.

Also, this paragraph could use explicit references for pidf-lo and
location URIs.

Section 4.3, paragraph 3: Please expand VPN on first use.

Table 1: Can you add a legend for o and m? I know it seems obvious, but
better to be explicit. Also, listing locationUriSet and presence both as
optional for responses does not quite capture the normative statement
that one or the other MUST exist.

Section 5.2: Should there be normative language around the inclusion of
locationType? (There is for the other parameters)


Section 6.2. "any" value: The normative statement that the LIS SHOULD
return all available forms seems to mildly conflict with some of the
further normative statements in the paragraph.
[MB] I'm not sure where the conflict is here.  They are all SHOULDs with
a couple MAYs and the last paragraph explains the reason for the
SHOULDs. [/MB]

Section 12.5: URI Scheme Syntax says "See section" with no section
number.

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