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Re: Last Call: <draft-nandakumar-rtcweb-stun-uri-05.txt> (URI Scheme for Session Traversal Utilities for NAT (STUN) Protocol) to Proposed Standard
2013-08-16 10:02:52
Hadriel,
I think you are making a fair case that this URI is more than just an internal
string for use in a single protocol, which is the impression I got from the
registration draft.
I think you're saying the URI schemes proposed provide ways for applications to
be told about NAT-traversal resources they should use? I can see that even if
their in-use deployment is limited, the benefits can be relevant to a wider
audience.
I think it would be useful if the URI scheme description could clarify that it
is being used to identify a NAT traversal service (or something like that).
#g
--
On 15/08/2013 14:16, Hadriel Kaplan wrote:
I agree with Harald.
Both the STUN and TURN URIs really do represent what we traditionally use URIs
for: they identify a physical resource, a protocol for accessing the resource,
etc. Unlike a data URL, the STUN/TURN URI is not locally/directly
self-contained data - it's a resource identifier, only meaningful when resolved
and accessed using the scheme's protocol and host address, with whatever
attributes are encoded in the URI.
Today only W3C has an immediate need for it, for the Javascript API for WebRTC,
but one can envision this might be used by others as well in the future:
1) SIP might use this in a UA-config profile to tell a SIP client what
STUN/TURN resources to use, or even in a REGISTER response someday.
2) XMPP might use this someday to indicate to clients what STUN/TURN servers to
use for Jingle/etc. Today it's done with a 'services' element I think, but it
could be changed in the future.
3) BEHAVE WG might define a new DHCP option to tell DHCP clients a STUN/TURN
server to use, in which case they could use this URI for that. (I don't know if
BEHAVE's already done that, or decided not to do such a thing, but just sayin'
it's another potential use-case)
It's possible other protocols might use this as well someday, for example RTSP
or H.323. I'm not saying any of them *will*, but it's possible.
-hadriel
On Aug 15, 2013, at 6:04 AM, Harald Alvestrand
<harald(_at_)alvestrand(_dot_)no> wrote:
On 08/15/2013 11:04 AM, Graham Klyne wrote:
Hi Harald,
On 14/08/2013 19:49, Harald Alvestrand wrote:
On 08/13/2013 12:14 AM, Graham Klyne wrote:
[...]
But, in a personal capacity, not as designated reviewer, I have to ask *why*
this needs to be a URI. As far as I can tell, it is intended for use only in
very constrained environments, where there seems to be little value in having
an identifier that can appear in all the contexts where a URI may be recognized.
The criteria for new URI schemes in http://tools.ietf.org/html/rfc4395 include:
"New URI schemes SHOULD have clear utility to the broad Internet community,
beyond that available with already registered URI schemes."
-- http://tools.ietf.org/html/rfc4395#section-2.1
This "utility to the broader community" is not clear to me, but I don't fully
understand the intended scope of this protocol, so I could be missing
something. So, in declaring consensus for this specification, I would request
that this aspect at least be considered.
I can only give my personal opinion....
1) This is a format for a piece of data. This data cannot be expressed using any
existing URI scheme - indeed, I don't think there exists another well-defined
textual representation of this piece of data.
1) This is defining an identifier that will be used in W3C-defined APIs. W3C
tends to use URIs every time they want a self-defining piece of data with a
clearly defined structure.
In the particular API where this is wanted, one wants to have STUN URIs, TURNS
URIs and TURN URIs passed over the same interface. Thus, keeping with the W3C
tradition of URIs seems reasonable.
I think this answers the question about "utility to the broader community" to my
satisfaction - your mileage may differ, of course.
Some thoughts occur to me:
1. My reading was that this is a generic NAT traversal protocol, so the requirement here
is not Web/W3C specific. But you do say "used in W3C-defined APIs"...
Truth in advertising: One W3C-defined API.
The specific reference:
http://dev.w3.org/2011/webrtc/editor/webrtc.html#dictionary-rtciceserver-members
2. If this is being driven by W3C activities, this should probably be flagged
with W3C TAG. I'll raise it there.
3. URIs are not generally used as *data* formats, but rather as identifiers for
resources. Web architecture and REST principles tend to discourage information
encoded in URIs in favour of data representation formats. Cf.
http://www.w3.org/TR/webarch/#uri-opacity,
http://www.w3.org/2001/tag/doc/metaDataInURI-31.html
Well, it is. The data encoded is the identification of a STUN server, which is
a resource.
4. If the purpose here is simply to encode data, then there does already exist
a suitable URI scheme, viz data:. A new content type can be defined to
actually encode the required data, and the whole be wrapped in a data: URI.
This approach has the advantage that alternative mechanisms (other than URIs)
can be used to transfer the traversal data if required (though that may be moot
in the very restricted intended scope of deployment for stun:, etc.)
Yes, but why?
...
Further, according to http://tools.ietf.org/html/rfc5389 it appears that there
are security considerations with regard to the STUN protocol that it should
not be used in isolation:
[[
Classic STUN also had a security vulnerability -- attackers could
provide the client with incorrect mapped addresses under certain
topologies and constraints, and this was fundamentally not solvable
through any cryptographic means. Though this problem remains with
this specification, those attacks are now mitigated through the use
of more complete solutions that make use of STUN.
For these reasons, this specification obsoletes RFC 3489, and instead
describes STUN as a tool that is utilized as part of a complete NAT
traversal solution.
]]
-- http://tools.ietf.org/html/rfc5389#section-2
It seems to me that creating a URI for STUN could encourage its use in
environments outside the "more complete solutions that make use of STUN".
This seems to be further reason that STUN[S] should not be a URI scheme.
I have also suggested that, if registered, the URI scheme registration should
carries a "health warning" to this effect, and that it is not suitable for
general use that is not part of a "complete NAT traversal solution". But I
also recognize that I do not fully grasp the security implications, and that
if those that do know better can agree that there is no potential for creating
security risks here, this suggestion may be unnecessary.
This URI scheme does not represent STUN. It represents configuration data that
is used to initialize a protocol machine that utilizes STUN.
This configuration data has to be passed no matter what the format of the data
is - whether it be URI or not.
Thus, I do not think the argument raised is really relevant to the context. The
data will be passed, and registering an URI scheme will cause no more and no
less data to be passed.
Again, my opinion.
If the URI is used only in very constrained contexts, then I agree.
But the whole point of using a URI is that, due to URI opacity, it can be used
a a range of contexts where URIs are used. If it cannot properly be used in
those other contexts, I have to question if it really is a URI, as opposed to a
string that happens to look like a URI.
The subject of "if it really is an URI" has plagued the whole URI space since
day one. My current opinion is that if it looks like an URI, and parses according to the
URI spec, it should probably be called an URI.
So far, we know of one context where we need this (RTCWEB). It's the first
context I know of where the Web and STUN intersect. It's not certain that it'll
be the last one.
I also note that this looks as if it may fall foul of the "confidential
metadata" practice noted in the W3C TAG finding about metadata in URIs
(http://www.w3.org/2001/tag/doc/metaDataInURI-31.html#hideforsecurity)
That's why we took the "credentials" part out of the URI scheme.
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