Re: H2 Implementation Debug State URI

Alex Rousskov <rousskov@measurement-factory.com> Tue, 09 August 2016 16:04 UTC

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To: Cory Benfield <cory@lukasa.co.uk>
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From: Alex Rousskov <rousskov@measurement-factory.com>
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Date: Tue, 09 Aug 2016 09:59:07 -0600
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Subject: Re: H2 Implementation Debug State URI
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On 08/09/2016 03:50 AM, Cory Benfield wrote:

> For those that don’t add support, they blindly forward the request
> on, running the risk of information leakage and invalid/incorrect
> responses.

I do not see how Max-Forwards unsupporting proxies can have a
significant negative effect on the problem you are trying to solve.
Obviously, you will not get their debugging state, but that is going to
happen no matter what -- there will always be proxies that do not
support your new feature. Why would Max-Forwards unsupporting proxies
produce invalid responses? They will just forward the response the next
hop gives them, and that response would be correct or incorrect
regardless of what they do.

AFAICT, Max-Forwards essentially lets you interrogate supporting hops.
Unless you change the protocol to require debugging support, nothing you
can do will let you interrogate unsupporting hops.

This overall problem feels very similar to traceroute -- it does not
always work and not all hops support ICMP TTLs, but it works well enough
in many cases to remain useful.

Alex.