Re: [TLS] ALPN - specifying client preference

[Andrei Popov <[e-mail]>]

Hi Ashok,

In ALPN, the server SHOULD select the protocol that the server prefers among the protocols advertised by the client. Having said that, the client sends its list of supported protocols in descending order of preference (most-preferred protocol first). This allows some freedom for the server-side implementer to take the client's preference into account, but ultimately the protocol selection occurs on the server.

In NPN, the client SHOULD select the first protocol advertised by the server that it also supports, i.e. the server's preferred protocol SHOULD be selected by the client. An exception to this is the case where the client does not support any of the server's protocols, in which case the client simply chooses the client's most preferred protocol. So there is an expectation that the client will honor the server's preference, but practically this depends on the client-side NPN implementation.

As for the client preferring "all protocols equally", can you elaborate on the scenario? What would the server do differently if it had this information?

Thanks,

Andrei

From: [e-mail] [mailto:[e-mail]] On Behalf Of Ashok Kumar
Sent: Monday, April 8, 2013 11:42 PM
To: [e-mail]
Subject: [TLS] ALPN - specifying client preference

With NPN, client could choose the protocol that it has better support for.

With ALPN, do we intend to add some mechanism where the client can specify its preference? I believe the order in which the protocols are sent give some preference, but is anyone interested in having options to say that client prefers all protocols equally?

Regards,
Ashok

P.S.: I'm new to TLS list and apologize if the query is not relevant. I was thinking more in lines of HTTP headers having qvalues.