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List:       postfix-users
Subject:    Re: Connection Cache with randmap -- Transport Use Appears Random
From:       Wietse Venema <wietse () porcupine ! org>
Date:       2020-08-16 19:34:20
Message-ID: 4BV6n82GYzzJrNy () spike ! porcupine ! org
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Viktor Dukhovni:
> On Sun, Aug 16, 2020 at 11:24:31AM -0700, Greg Sims wrote:
> 
> > This date contradicts some recommendations on the Internet of turning
> > off the Connection Cache when randmap is used to "increase
> > randomness".
> 
> The connection cache has zero impact on transport selection, connections
> are *never* reused across transports.  The transport name is part of the
> connection cache lookup key.  All sorts of people, who half-know what
> they're talking about, write HOWTO documents explaining how to do some
> task in a half-arsed way. :-(

Confirmed. The master.cf service name (i.e. transport name) is 
an unconditional part of the connection cache lookup key.

For cache lookup by destination name:

#define SMTP_KEY_MASK_SCACHE_DEST_LABEL \
        (SMTP_KEY_FLAG_SERVICE | COND_SASL_SMTP_KEY_FLAG_SENDER \
        | SMTP_KEY_FLAG_REQ_NEXTHOP)

For cache lookup by server IP address:

#define SMTP_KEY_MASK_SCACHE_ENDP_LABEL \
        (SMTP_KEY_FLAG_SERVICE | COND_SASL_SMTP_KEY_FLAG_SENDER \
        | COND_SASL_SMTP_KEY_FLAG_CUR_NEXTHOP \
        | COND_SASL_SMTP_KEY_FLAG_HOSTNAME \
        | COND_TLS_SMTP_KEY_FLAG_CUR_NEXTHOP | SMTP_KEY_FLAG_ADDR | \
        SMTP_KEY_FLAG_PORT | SMTP_KEY_FLAG_TLS_LEVEL)

So yeah, some information on the Internet is incorrect.

	Wietse
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