Re: [tsvwg] Comment on draft-ietf-tsvwg-transport-encrypt

Tom Herbert <tom@herbertland.com> Sat, 29 February 2020 00:17 UTC

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From: Tom Herbert <tom@herbertland.com>
Date: Fri, 28 Feb 2020 16:17:42 -0800
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To: Erik Kline <ek.ietf@gmail.com>
Cc: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>, tsvwg <tsvwg@ietf.org>
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Subject: Re: [tsvwg] Comment on draft-ietf-tsvwg-transport-encrypt
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On Fri, Feb 28, 2020, 4:10 PM Erik Kline <ek.ietf@gmail.com> wrote:

> It also seems possible that some UDP options (
> https://tools.ietf.org/html/draft-ietf-tsvwg-udp-options) might come
> along that could help things like QUIC effectively have a path-modifiable
> portion that (a) isn't a HbH extension header and (b) isn't covered by
> something cryptographic that would break if it were modified in-flight.
>

Erik,

"things like QUIC" would mean protocols encapsulated in UDP. The point of
HBH is that it works transparently for _all_ transport protocols whether
they are encrypted. Besides, UDP options hasn't yet been proven deployable,
so good chance it would just be trading one set of problems for another...

Tom


> On Fri, Feb 28, 2020 at 1:03 PM Spencer Dawkins at IETF <
> spencerdawkins.ietf@gmail.com> wrote:
>
>> Hi, Tom,
>>
>> On Fri, Feb 28, 2020 at 2:31 PM Tom Herbert <tom@herbertland..com
>> <tom@herbertland.com>> wrote:
>>
>>> While the draft certainly has improved both in tone and content, I
>>> still feel like there is one area that is very under-represented.
>>> Namely the possibility of using extension headers to carry necessary
>>> transport information that the network needs. I have brought this up
>>> several times, and don't believe it has been adequately addressed.
>>>
>>> Section 5 discusses extension headers (in a rather offhand manner). It
>>>
>>
>> You're talking about Section 5.2, right?
>>
>>
>>> is presented in a very negative light focused on the why they won't
>>> work. The crux of the argument in the draft is that extension headers
>>> are not deployable, RFC7872 is referenced as the basis for that
>>> conclusion. But as we pointed out, and even acknowledged in the draft
>>> text now, that is from 2016, so the data and questionable. But even if
>>> it were still relevant the conclusion drawn from it that EHs are not
>>> usable in any form is highly debatable.
>>>
>>> What the draft fails to mention is that Hop-by-Hop extensions headers
>>> are the ONLY protocol conformant way to signal intermediate nodes with
>>> data, including transport layer information, other than what is
>>> contained in the IP header. Intermediate nodes that parse packets
>>> beyond the network layer are not protocol conformant. This is not just
>>> an academic purist statement, this is DPI which is what has led to
>>> protocol ossification and hence is a primary motivation for transport
>>> headers being encrypted in the first place (see QUIC reasoning on
>>> this). Extension headers are also being dismissed because of protocol
>>> non-conformance in intermediate nodes. As often noted, RFC8200 has
>>> relaxed requirements concerning HBH options so that intermediate nodes
>>> can ignore. I believe that RFC8200 was published after RFC7828
>>> potential impact of that change was not measured.
>>>
>>> So then one interpretation of the draft is that it is trying to
>>> justify one type of protocol non-conformance, on the basis it is
>>> useful in practice, yet on the other hand rejects the correct solution
>>> to the problem on the because of another type of protocol
>>> non-conformance making it not deployable. There seems to be a
>>> significant irony at work here.
>>>
>>
>> ISTM that the draft (if we're talking about 5.2) is talking about
>> interdomain use of hop-by-hop extension headers, which might reasonably be
>> deployed in a domain that you make decisions about (the subject of 5.1),
>> but are (let's say) more challenging to deploy if you're expecting them to
>> work between arbitrary endpoints attached to arbitrary domains,
>> interconnected over arbitrary topologies.
>>
>> I don't disagree with the points you're making, but ISTM that if the
>> working group wants to say hop-by-hop extension headers can be a plan, that
>> should appear in 5.1, unless someone can point to at least one success
>> story of hop-by-hop extension headers being widely deployed and used across
>> domain boundaries.
>>
>> Best,
>>
>> Spencer
>>
>>
>>> Tom
>>>
>>>