Re: [TLS] SNI and ALPN -- which firsr?

Martin Thomson <martin.thomson@gmail.com> Wed, 30 July 2014 16:22 UTC

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Date: Wed, 30 Jul 2014 09:22:42 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: "Salz, Rich" <rsalz@akamai.com>
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Subject: Re: [TLS] SNI and ALPN -- which firsr?
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On 29 July 2014 18:57, Salz, Rich <rsalz@akamai.com> wrote:
> Is there a fixed order for processing a hello that has both ALPN and SNI?
>
> For example, if you do ALPN first, then the SNI might end up “pointing to” a
> client with weaker ciphers than, say HTTP/2 allows.
>
> On the other hand, I can see the case that the SNI is protocol-specific, so
> you should do ALPN first.

I don't think that order of processing needs to be fixed, or the same
for different deployments.  I can imagine that some deployments might
want to have a table that uses both inputs simultaneously.  Specifying
a fixed processing order removes some flexibility.

Is there a particular reason that a fixed order would be of an advantage?