Hi Ekr, hi all,
(not sure anymore which email best to reply to but I'm using this one now to
partly also reply to others).
See below.
On 27.04.2017 14:51, Eric Rescorla wrote:
On Thu, Apr 27, 2017 at 1:32 AM, Mirja Kühlewind <i...@kuehlewind.net
<mailto:i...@kuehlewind.net>> wrote:
I do see the problem you have and I understand why you selected the
solution you have but that does contradict quite a bit the idea of the
port registry and I don't think it's a safe and future prove solution.
Even if people use this approach, I'm concern to publish it in an
Standards Track RFC, but I guess that's a discussion the IESG would need
to have.
Mirja,
I agree that this kind of port squatting is regrettable, but I also don't
think it really
helps to not publish RFCs that document widely used protocols because we
are sad they port-squatted.
I proposed a way to deal with this in an earlier e-mail. Would that be
satisfactory
to you. To retransmit, we add the following
"Note: While port 4500 is the reserved port for this protocol, some existing
implementations
also use port 443. The Stream Prefix provides some mitigation against
cross-protocol
attacks in this case, however, the use of port 443 is NOT RECOMMENDED"
We could do something similar for port 80.
Would that work?
This already is good but I think it's not enough. As Tero noted the working
group thought that they rather specify a generic scheme which I find
problematic. Currently the drafts says:
"This document leaves the selection of TCP ports up to
implementations. It is suggested to use TCP port 4500, which is
allocated for IPsec NAT Traversal."
Which sounds to me like an invitation to squat on any open port regardless
what the port is supposed to be used for (hoping that the magic number would
avoid any collision). I don't think that a good thing to right in an RFC.
Now given the text you propose above, I actually assume that the text I just
cited will be removed but the whole document is written with this assumption
and therefore there are a couple more places where wording probably needs to
change.
I do understand well the problem and that 443 is used in practice. However,
to match reality I would rather like to see a document that specifies the
approach of encapsulating in TLS/TCP on port 443 that is used today and pure
TCP encapsulation for use with port 4500 only. Again i think that's where
your proposed text is heading to but I think it needs more changes; in this
case it would also make sense to add the TLS part back in the main document
for 443 only.
Further, I have one more question: The document is written in a way that
allows the implementation of multiple services on the used port. Is that
actually done in reality? If we could restrict the use of this encapsulation
with servers that only are IKE servers (at least for the used port), you
would actually not need the magic number anymore. I guess you can still have
the magic number if you really want it because that makes it easier to
distinguish valid IKE/IPSec traffic from other random traffic that might be
send to this port but the other service running on this port (on other
servers) does not need to know about the magic number because it is supposed
to never see any IKe/IPSec TCP-encapsulated traffic.
Does that make sense?
Mirja
-Ekr
Mirja
We can soften the references in the appendix to the fact that other
ports may, in fact, be used. As for the configuration, it should
state 4500 as the default, but allow peers to configure something
else out-of-band if they want to modify behavior (which is standard
even in UDP implementations of IKE).
Further, as also mentioned in the tsv-art review (Thanks Wes!), this
draft does not sufficiently handle the case of TCP in TCP
encapsulation.
Here a copy of the tsv-art review:
Reviewer: Wesley Eddy
Review result: On the Right Track
This document is clear and well-written. It can easily be
implemented
based on the description.
There are a few additional issues that should be considered with
advice to implementers in Section 12 on performance considerations:
1) Invisibility of packet loss - Inner protocols that require packet
losses as a signal of congestion (e.g. TCP) will have a challenge
due
to not being able to see any packet losses since the outer TCP will
repair them (unless sending into a full outer TCP socket buffer
shows
up back to the inner TCP as a packet loss?).
Yes, this is definitely true. We try to capture that with the line:
"This will make loss-
recovery of the inner TCP traffic less reactive and more prone to
spurious retransmission timeouts."
However, this can certainly be expanded upon.
2) Nesting of ECN - Inner TCP connections will not be able to use
effectively ECN on the portion of the path covered by the outer TCP
connection.
Generally, IPsec tunnels will apply RFC 6040 for translating ECN
markings between inner/outer packets. Since TCP encapsulation places
the inner IP packets in a stream, there isn't a direct mapping.
An implementation could try to roughly map, but it may be best to
suggest that the ECN markings for inner and outer packets be left
separate. What is your opinion?
3) Impact of congestion response on aggregate - The general "TCP in
TCP" problem is mentioned, and is mostly appropriate for a single
flow. If an aggregate of flows is sharing the same outer TCP
connection, there may be additional concerns about how the
congestion
response behavior impacts an aggregate of flows, since it may cause
a
shared delay spike even to low-rate flows rather than distributing
losses proportional to per-flow throughput.
Indeed. We can add further comments to that effect.
4) Additional potential for bufferbloat - Since TCP does not bound
latency, some applications in the IPsec-protected aggregate could
drive latency of the shared connection up and impact the aggregate
of
flows that may include real-time applications. The socket buffer
for
the outer TCP connection might need to be limited in size to ensure
some bounds?
We can add a comment to suggest that the buffering should be limited
on the outer connection if possible.
Not addressing these could lead to poor experiences in deployment,
if
implementations make wrong assumptions or fail to consider them.
I do think all of these concerns go back to the overall
recommendation of "use direct ESP or UDP Encapsulation whenever
possible". Anything to help back up that point is great!
Thanks,
Tommy
In the security considerations section, there are several RFCs on
mechanisms to increase robustness to RST attacks and SYN floods that
could be mentioned if it's worthwhile.
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