owner-radiusext(_at_)ops(_dot_)ietf(_dot_)org <> scribbled on Tuesday, April
29, 2008
12:02 AM:
Last but not least, this draft fairly universally violates several
of the guidelines given in
http://www.ietf.org/internet-drafts/draft-ietf-radext-design-02.txt,
in particular those regarding the use of tags to associate different
attributes (called "Index" in this document) and the creation of
"complex" attributes.
The issue of "complex attributes" was extensively discussed on
the RADEXT WG mailing list, and the Design Guidelines are
based on the WG consensus that was derived from the review
of this document.
In particular, Section 2.1.3 of the Design Guidelines document
specifically calls out the distinction between complex
attributes which are interpreted by RADIUS, as opposed to
"opaque data" which is treated as a string by RADIUS, and
interpreted out of band:
The only other exception to the recommendation against complex types
is for types that can be treated as opaque data by the
RADIUS server.
For example, the EAP-Message attribute, defined in [RFC3579] Section
3.1 contains a complex data type that is an EAP packet. Since these
complex types do not need to be parsed by the RADIUS server, the
issues arising from policy language limitations do not arise.
Similarly, since attributes of these complex types can be configured
on the server using a data type of String, dictionary
limitations are
also not encountered. Section A.1 below includes a series of
checklists that may be used to analyze a design for RECOMMENDED and
NOT RECOMMENDED behavior in relation to complex types.
If the RADIUS Server simply passes the contents of an attribute to
some non-RADIUS portion of the network, then the data is opaque, and
SHOULD be defined to be of type String. A concrete way of judging
this requirement is whether or not the attribute definition in the
RADIUS document contains delineated fields for sub-parts of
the data.
If those fields need to be delineated in RADIUS, then the
data is not
opaque, and it SHOULD be separated into individual RADIUS
attributes.
I'm quite aware of that & if, in fact, the attributes were opaque data
that passage would certainly cover it. However, it doesn't appear that
either the Location-Information nor the Location-Data Attribute is
actually "opaque".
I realize that the RADIUS design guidelines document is just an
Internet-Draft, but it is a radext WG document & has been under
construction for some period of time.
The Design Guidelines document text was specifically crafted
based on this particular draft, based on extensive discussion
within the RADEXT WG.
More important than
the standardization status of the document is the question of whether
the guidelines make sense;
The Design Guidelines document has completed RADEXT WG last
call with only minor comments outstanding. If you had any
concerns about whether the document "makes sense" you should
have raised them long ago -- but you did not.
I wasn't referring to myself: I've reviewed that document several times
and have yet to find anything to complain about ;-). I do not, however,
pretend to know the opinions of your co-authors or even your own, for
that matter: AFAIK, it's not mandatory for a WG Chair to like all of the
WG documents, just to ensure that they reflect WG consensus.
if so, then it may not be such a good idea to so completely ignore
them;
Far from ignoring the Design Guidelines, this document has
actually been one of the primary motivations for creating them
-- and the text in Design Guidelines has been specifically
crafted to deal with this particular case.
If not, then maybe radext should rethink this work item (especially
since a co-chair of that WG is also a co-author of the document
under review).
Given the extensive discussion on the RADEXT WG list relating
to this document and Design Guidelines, I have personally
spent quite a bit of time with Hannes, Avi and others working
on improving the compatibility of this document with the
Design Guidelines.
I did not ask to be named as an author -- the other authors
suggested this to me.
I don't think that I suggested that you had -- in fact I noted the
(perhaps over ;-) enthusiastic appreciation of your efforts by your
co-authors in my first message.
Given that, I have no particular interest in this document,
other than ensuring that it does as little violence to the
RADIUS protocol as possible.
So if you have particular concerns relating to the handling of
this document,
I don't think suggested that, either...
or can provide specific instances in which this
document violates "Design Guidelines" (applying the tests in
Appendix A, for example), please put them on the table.
OK. As you noted above, the Design Guidelines say
If the RADIUS Server simply passes the contents of an attribute to
some non-RADIUS portion of the network, then the data is opaque, and
SHOULD be defined to be of type String. A concrete way of judging
this requirement is whether or not the attribute definition in the
RADIUS document contains delineated fields for sub-parts of the data.
If those fields need to be delineated in RADIUS, then the data is not
opaque, and it SHOULD be separated into individual RADIUS attributes.
But section 4.7 of the draft under review says
o If the RADIUS server requires location information for computing
the authorization decision and the RADIUS client does not provide
it with the Access-Request message then the Requested-Location-
Info Attribute is attached to the Access-Challenge with a hint
about what is required. Two cases can be differentiated:
1. If the RADIUS client sends the requested information then the
RADIUS server can process the location-based attributes.
2. If the RADIUS server does not receive the requested
information in response to the Access-Challenge (including the
Requested-Location-Info Attribute) then the RADIUS server may
respond with an Access-Reject message with an Error-Cause
Attribute (including the "Location-Info-Required" value).
The RADIUS server "requires location information for computing the
authorization decision". How can it make a decision based upon data
that it cannot understand? It doesn't have to because "[i]f the RADIUS
client sends the requested information then the RADIUS server can
process the location-based attributes". Of course, "process" can mean
many things and if these attributes are opaque then "process" might mean
just writing the data to a file or forwarding it over some unspecified
interface to another entity. So maybe the RADIUS server is making the
decision based just upon the fact that it received a
Location-Information/Location-Data pair in the new Access-Request (along
with the echoed Attributes). The problem is that the RADIUS server
didn't request just any old location data; it requested a very specific
set of data (in the example later in section 4.7 it is the civic
location of the user). AFAICT, the only way that the RADIUS server can
tell if it has actually received the information it requested is to
examine the Code and Entity sub-fields of the returned
Location-Information Attribute and check that there is an associated
instance of the Location-Data Attribute by matching the Index fields of
the Attributes. Remember that this check for the requested information
takes place before the RADIUS server processes the data; this suggests
to me that these fields "need to be delineated in RADIUS" and therefore
"the data is not opaque, and it SHOULD be separated into individual
RADIUS attributes". Further, section A.2.2 of the Design Guidelines
asks the (how I wish it was a musical ;-) question:
Does the attribute define a complex data type for purposes other than
authentication or security? If so, this data type SHOULD be replaced
with simpler types, as discussed above in Section A.2.1.
Neither the Location-Information nor the Location-Data Attributes seem
to be used for authentication (authorization != authentication) or
security. Section A.1.3 of the same document says (WRT Attributes
encapsulating complex data types):
Does the attribute encapsulate an existing data structure defined
outside of the RADIUS specifications? Can the attribute be treated
as opaque data by RADIUS servers (including proxies?) If both
questions can be answered affirmatively, a complex structure MAY be
used in a RADIUS specification.
The specification of the attribute SHOULD define the encapsulating
attribute to be of type String. The specification SHOULD refer to an
external document defining the structure. The specification SHOULD
NOT define or describe the structure[...]
However, section 4.2 of draft-ietf-geopriv-radius-lo describes the
structure of the Location-Information Attribute in detail; the question
of opacity was dealt with above.
WRT the Index fields of the Location-Information and Location-Data
Attributes, the fact that they are both mandatory and large avoids many
of the drawbacks mentioned WRT tags in the Design Guidelines document,
nevertheless that document does state 'new attributes SHOULD use the
grouping method described in
http://www.ietf.org/internet-drafts/draft-ietf-radext-extended-attribute
s-03.txt'.
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