[TLS] SNI and ALPN -- which firsr?

"Salz, Rich" <rsalz@akamai.com> Wed, 30 July 2014 01:57 UTC

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From: "Salz, Rich" <rsalz@akamai.com>
To: "TLS@ietf.org (tls@ietf.org)" <tls@ietf.org>
Date: Tue, 29 Jul 2014 21:57:37 -0400
Thread-Topic: SNI and ALPN -- which firsr?
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Subject: [TLS] SNI and ALPN -- which firsr?
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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.

Thoughts?  Is this something we need to specify?  Or give general advice for the processing order of extzensions?

--
Principal Security Engineer
Akamai Technologies, Cambridge MA
IM: rsalz@jabber.me<mailto:rsalz@jabber.me> Twitter: RichSalz