Christian,
Thanks for the comments. Responses inline.
On Wed, Apr 1, 2009 at 3:19 AM, Christian Huitema
<huitema(_at_)windows(_dot_)microsoft(_dot_)com> wrote:
I tend to agree with Cullen on some points. Instead of a draft presenting a
set of algorithm, I would rather see a draft presenting a set of tools that
can be useful for characterizing local connectivity, and presenting these
tools as justifying a new set of STUN options that applications developers
could then use as they see fit.
So most people miss this, which may mean it needs to be clarified more
somehow, but the algorithm section is actually not normative. The
STUN attributes and their processing is normative, but the intention
has always been that the algorithms be an example of what you can do
with them, but not necessarily the only thing you can do with them,
although probably a good starting point. (In fact, a few people have
suggested more complex tests using the existing attributes, but I've
hesitated to put anything like that in there.)
Within that structure, does that essentially meet what you're thinking
of? Certainly some verbiage can be added to emphasize this point
more---since it's a common question, maybe it should be added. It
would be possible to reverse the order, I suppose, and do things in
the other direction, although then for people who didn't follow the
whole 3489 evolution, I think it might be a really hard read to define
a bunch of stuff without explaining how it should be used.
The draft proposes a set of algorithms to characterize a NAT. As Cullen
points out, any of these algorithms has weaknesses. The main weakness is that
the behavior of NAT is often transient, e.g. different port mapping
algorithms depending on whether or not the internal tables are near
saturation, or not. So, any attempt to present an algorithm as a definitive
classifier is, by nature, weak. On the other hand, even weak attempts are
useful, especially in peer-to-peer applications, but also for network
management and debugging. There is a tradeoff between resource consumed and
precision of the characterization. This tradeoff is largely for the
application developers and users to decide.
I think we are in agreement here. The real test will be how
application protocols are designed to make use of these techniques. I
have some ideas for how they would be designed in P2PSIP, but haven't
written anything up yet, trying to focus on just getting the basic
mechanism in.
What I would like to see happen is sort of like the UNSAF IAB
considerations. If you're going to use these STUN attributes, you
must answer these questions. I don't know if that's really necessary
since this draft is experimental---there will be enough of a "wait,
how are you using this experimental protocol?" that I think future
drafts will get scrutiny, and in fact that has already flagged a
couple of drafts as questionable already.
The interesting question is, what mechanisms do application developers need,
in addition to the basic response system defined in STUN? Most of these new
mechanisms fall direct a server to send packets to a different address, to a
different port, or at a different time, plus indeed a negotiation mechanism
to determine whether such mechanisms are available. I don't see much harm in
defining these mechanisms and the corresponding options. Indeed, I see some
goodness in defining them once, in the IETF.
The main goodness comes form a way to control the use of the mechanisms.
Sending responses to a different address, to a different port, or at a
different time has a risk. Such mechanisms can be used for denial of service
attacks. If we are convinced that the draft mitigates such denial of service
attacks, then we should register the corresponding attributes.
I believe the authentication and CACHE-TIMEOUT mechanisms in the draft
are sufficient for preventing DoS, and there was consensus for that
the last time the change was made and presented a few meetings ago,
but welcome any further comments on the issue.
Bruce
-----Original Message-----
From: behave-bounces(_at_)ietf(_dot_)org
[mailto:behave-bounces(_at_)ietf(_dot_)org] On Behalf
Of Dan Wing
Sent: Tuesday, March 31, 2009 8:09 PM
To: behave(_at_)ietf(_dot_)org
Cc: draft-ietf-behave-nat-behavior-discovery(_at_)tools(_dot_)ietf(_dot_)org
Subject: [BEHAVE] FW: Last Call: draft-ietf-behave-nat-behavior-
discovery (NATBehavior Discovery Using STUN) to Experimental RFC
Forwarded for those that don't follow the main IETF list.
Please reply to the list if you agree or disagree with the points raised
by
Cullen. Thanks.
-d
-----Original Message-----
From: ietf-bounces(_at_)ietf(_dot_)org
[mailto:ietf-bounces(_at_)ietf(_dot_)org] On Behalf Of
Cullen
Jennings
Sent: Tuesday, March 31, 2009 9:53 AM
To: IETF Discussion; IESG IESG
Subject: Re: [BEHAVE] Last Call: draft-ietf-behave-nat-behavior-
discovery
(NATBehavior Discovery Using STUN) to Experimental RFC
I was somewhat shocked to see the draft in IETF Last Call. The last
time this draft was discussed at the microphone in Behave, many people
were very concerned that it id not possible to correctly characterize
a NAT without using more than one address behind the NAT. The tests
done on on NATs by the researches at MIT did that, so did the the
stuff from Cornell, as did draft-jennings-behave-test-results. The
reason why this was needed is largely the reason why the IETF invented
ICE. Initially folks thought that STUN alone would be enough to do NAT
traversal. This turned out not to be true, STUN deprecated those parts
and ICE was started. This draft fails to describe the types of test
that have actually been found to work and just reinstates the stuff
that was deployed and failed and then deprecated out of STUN.
Now this draft pays some lip service to the fact that it basically
won't work. You can read section 1 and get the full idea. The first
and 2'nd par basically say this won't work. Then para 3 proposes this
is experiment to find out something we already know the answer to.
When this work was chartered, it was about making a way to
characterize NATs and describe them in a controlled lab like
environment. It was not about resurrecting exactly the part of STUN
that had been tried, failed , and deprecated.
Specific problems with the draft....
2.2 - this just won't work. The test described in this draft will not
find out if the node is behind an endpoint independent nat. I have
specific nats where it won't work. I have explained to the authors why
it won't work. The answer I get back is "it might work some of the
time". It true it might work some of the time but we all agree there
are many NATs for which it will not work.
Other section that don't work are 3.1, 3.2, 3.3, 3.4, 3.5, 3.5 - uh
all of them actually. I'm glad to provide details on why they don't
work but I have in the past and we not really debating if they work or
not. The authors believe there is sufficient text at the beginning of
the draft in section 1 that it is OK that these fail in many cases and
don't need to be mentioned again. We not debating these work some of
the but not all the time - everyone agrees on that.
Section 4.1 - The results in here will be just wrong for ports
different than the one the test was run on. The response to this was
to add "use same port when possible". That's not going to exactly
cause applications to work.
Section 4.2 - Can't really separate the topic from if UDP is blocked
from if the STUN server is down.
Section 4.4 - this fails if the port was recently used for similar
tests from same stun server. There no way to know this as an
application. This type of test can work in lab condition where all
traffic on NAT is controlled but it operational networks it will fail.
It is possible to do timing testing using just the change ip flag. The
REPSONSE-TARGET stuff is not needed and open up the possibility to
have a STUN server send packets to places that it should not which
causes IDS system to black list all traffic from the STUN server thus
making it unusable for other clients. The ability to tell the STUN
server to send packets to arbitrary locations would be fine for a
system in a lab used to characterize a NAT but is not a good idea for
internet deployed STUN servers.
The bulk of these issues were sent Aug 28 to behave list during the
2nd WGLC. I requested agenda time during IETF 74 to discuss these
issues but it was denied.
In summary -The approaches described in this draft are known to fail
with many NATs. I don't see any evidence of the WG actually having
read this draft much less have consensus on the approach in it. I
think the WG should spend meeting time to discuss the topic and decide
what to do. The key topic in my mind is we are defining a document
that allows us to characterize a NAT in a lab or if we are trying to
make something that works in field and can be used to aid NAT
traversal in applications.
Cullen <in my roll as individual contributor and ex chair of behave>
On Mar 10, 2009, at 8:44 AM, The IESG wrote:
The IESG has received a request from the Behavior Engineering for
Hindrance Avoidance WG (behave) to consider the following document:
- 'NAT Behavior Discovery Using STUN '
<draft-ietf-behave-nat-behavior-discovery-06.txt> as an Experimental
RFC
The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to
the
ietf(_at_)ietf(_dot_)org mailing lists by 2009-03-31. Exceptionally,
comments may be sent to iesg(_at_)ietf(_dot_)org instead. In either case,
please
retain the beginning of the Subject line to allow automated sorting.
The file can be obtained via
http://www.ietf.org/internet-drafts/draft-ietf-behave-nat-behavior-
discovery-0
6.txt
IESG discussion can be tracked via
https://datatracker.ietf.org/public/pidtracker.cgi?command=view_id&dTag=
15728&
rfc_flag=0
The following IPR Declarations may be related to this I-D:
https://datatracker.ietf.org/ipr/919/
https://datatracker.ietf.org/ipr/945/
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