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Re: setting up postscreen on a system with multiple external interfaces

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  • Noel Jones
    ... You ve shared too much. By now no one has any idea what you re doing. Overview: Postscreen is a front-end listener for smtpd. It s not a proxy. Incoming
    Message 1 of 25 , Feb 21, 2013
      On 2/21/2013 10:46 AM, Erik Slagter wrote:
      > Another variation I tried ("pass" and "postscreen" the other way
      > around).


      You've shared too much. By now no one has any idea what you're doing.

      Overview:

      Postscreen is a front-end listener for smtpd. It's not a proxy.
      Incoming connections are handled by postscreen until postscreen
      either decides it's clean and passes the connection endpoint to
      smtpd, or rejected. This is covered in more detail in the
      POSTSCREEN_README.

      When postscreen decides to pass the connection to smtpd, postscreen
      is no longer involved, and smtpd has no knowledge of what transpired
      between postscreen and a client.


      Solution:

      [this is not a complete how-to, but will show you how to use
      multiple interfaces]

      At some point you reported:


      > mx1.ipv4.slagter.name:smtp inet n - n - 2 smtpd
      > -o myhostname=eriks.xs4all.nl
      > -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv4-25
      > -o smtpd_tls_security_level=may

      Ok.

      > -o postscreen_tls_security_level=may
      > -o tlsproxy_tls_security_level=may

      both these belong in main.cf, or better, set main.cf:
      "smtpd_security_level = may" and leave these at their defaults.

      > -o smtpd_proxy_filter=nemesis.ipv4:10025
      > -o soft_bounce=no
      > -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv4

      The cache map parameter belongs in main.cf. Probably a mistake to
      create separate caches.

      Same comments as above for the smtpd listener below.

      >
      > mx1.ipv6.slagter.name:smtp inet n - n - 2 smtpd
      > -o myhostname=mx1.ipv6.slagter.name
      > -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv6-25
      > -o smtpd_tls_security_level=may
      > -o postscreen_tls_security_level=may
      > -o tlsproxy_tls_security_level=may
      > -o smtpd_proxy_filter=nemesis.ipv4:10025
      > -o soft_bounce=no
      > -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv6



      For the TLS part, it will be much easier to turn TLS on in main.cf,
      then turn it off on the interfaces where you don't want to offer it
      with "-o smtpd_tls_security_level=none".

      # main.cf
      smtpd_tls_security_level = may

      For the greeting banners, set them as macros in main.cf and then
      refer to them by $name in master.cf

      # main.cf
      postscreen_greet_v4 = postscreen.v4.mx1 ESMTP greets you
      postscreen_greet_v6 = postscreen.v6.mx1 ESTMP greets you


      Now tell postscreen which ports to listen on and to enable the banner:

      # master.cf

      mx1.ipv4.slagter.name:smtp inet n - n - 1 postscreen
      -o postscreen_greet_banner=$postscreen_greet_v4

      mx1.ipv6.slagter.name:smtp inet n - n - 1 postscreen
      -o postscreen_greet_banner=$postscreen_greet_v6



      Next we tell smtpd to get it's connections from postscreen.
      On your existing "smtp ... smtpd" entries where you want postscreen,
      change the "smtp inet n" part to "smtp pass -"
      This is described in detail in
      http://www.postfix.org/POSTSCREEN_README.html#config

      so your existing entry:
      > mx1.ipv4.slagter.name:smtp inet n - n - 2 smtpd

      would become:
      mx1.ipv4.slagter.name:smtp pass - - n - 2 smtpd




      Good luck.



      -- Noel Jones
    • Erik Slagter
      ... Yes I blame the documentation, but not the software. I ve been using postfix for, well, something like ten years or more, I think it s the best thing since
      Message 2 of 25 , Feb 21, 2013
        On 21-02-13 19:17, DTNX Postmaster wrote:

        > You keep blaming the documentation and the software, when the problem
        > is most likely in your understanding of it.

        Yes I blame the documentation, but not the software. I've been using
        postfix for, well, something like ten years or more, I think it's the
        best thing since sliced bread, especially compared to sendmail, qmail
        and exchange.

        The way I've configured it now, really suits the demands. I cannot
        remember any phrases in the documentation recommending not to do it this
        way (i.e. start multiple smtp listeners on different addresses with
        different options, in one master process). If it actually appears to be
        disrecommended, then that's clear to me, no problem.

        > Simplify your configuration. Don't assume that what goes for 'smtpd'
        > goes for 'postscreen' as well.

        I'd like to, but where do I find what I CAN assume? The factual
        documentation of postscreen is so sparse, it's mostly HOWTO,
        monkey-see-monkey-do.

        > Pick sensible defaults for 'main.cf',
        > and override only the options that are absolutely necessary.

        That's already done.

        > If you have a legitimate reason (as in, contractual obligations or
        > whatnot) to require seperate hostnames, greetings, TLS settings and
        > such, use the multi-instance features and seperate them. Otherwise the
        > KISS principle applies.

        Actually this way is much more KISS to me than running multiple
        instances of "master".

        I'm starting to think that the reason this operation is not documented,
        is because it's not possible. It looks like the postscreen layer
        literaly sits between the remote client and the smtp process, and the
        information where the connection took place (interface/address) is not
        available at the point where the smtpd is invoked.

        If that's the case, postscreen is not the way to go for me. I assumed
        postscreen was implemented a bit like proxy-filter, where you can run
        any number of filters on any number of addresses.
      • Erik Slagter
        ... I m just following the REPORT A PROBLEM procedure I was kindly pointed at... ... Yes at this point the smtpd/master has no knowledge of the
        Message 3 of 25 , Feb 21, 2013
          On 21-02-13 19:30, Noel Jones wrote:

          > You've shared too much. By now no one has any idea what you're doing.

          I'm just following the "REPORT A PROBLEM" procedure I was kindly pointed
          at...

          > When postscreen decides to pass the connection to smtpd, postscreen
          > is no longer involved, and smtpd has no knowledge of what transpired
          > between postscreen and a client.

          Yes at this point the smtpd/master has no knowledge of the
          interface/address, that's exactly the thing I fear.

          > At some point you reported:
          > [ .. ]
          >> -o postscreen_tls_security_level=may
          >> -o tlsproxy_tls_security_level=may
          >
          > both these belong in main.cf, or better, set main.cf:
          > "smtpd_security_level = may" and leave these at their defaults.

          Tried both, doesn't matter. The thing is that what way you set the smtpd
          options (in main.cf) you cannot override them with postscreen. So if you
          set the default value suitable for address a and b, they must be
          override for address c and d and vv. Yes, I have some internal address
          that need to have tls_security=none and yes, that works like a charm
          without postscreen enabled.

          >> -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv4
          >
          > The cache map parameter belongs in main.cf. Probably a mistake to
          > create separate caches.

          Nope, the cache map cannot be shared between two smtpd processes (see
          documentation ;-)). It's not a problem though, because one db holds ipv4
          addresses and the other is ipv6 addresses.

          > For the TLS part, it will be much easier to turn TLS on in main.cf,
          > then turn it off on the interfaces where you don't want to offer it
          > with "-o smtpd_tls_security_level=none".

          All relevant options for tls are actually set in main.cf. It's only that
          it's not enabled there, it's enabled on a per-address base. Which works.

          > For the greeting banners, set them as macros in main.cf and then
          > refer to them by $name in master.cf

          That's a possibility, but it's not necessary and doesn't solve the problem.

          > Now tell postscreen which ports to listen on and to enable the banner:
          >
          > # master.cf
          >
          > mx1.ipv4.slagter.name:smtp inet n - n - 1 postscreen
          > -o postscreen_greet_banner=$postscreen_greet_v4
          >
          > mx1.ipv6.slagter.name:smtp inet n - n - 1 postscreen
          > -o postscreen_greet_banner=$postscreen_greet_v6
          >
          > Next we tell smtpd to get it's connections from postscreen.
          > On your existing "smtp ... smtpd" entries where you want postscreen,
          > change the "smtp inet n" part to "smtp pass -"
          > This is described in detail in
          > http://www.postfix.org/POSTSCREEN_README.html#config
          >
          > so your existing entry:
          >> mx1.ipv4.slagter.name:smtp inet n - n - 2 smtpd
          >
          > would become:
          > mx1.ipv4.slagter.name:smtp pass - - n - 2 smtpd

          I get your drift, but IIRC I already tried this (multiple times, with
          slight variations) and also reported about the outcoming of that:
          "fatal: address already in use".

          Did I already mention I have followed all the steps from the README as
          closely as possible?
        • Viktor Dukhovni
          ... Take a DEEP breath, relax and don t *try* implementing new configurations you don t yet understand. The shots in the dark will just get you more confused.
          Message 4 of 25 , Feb 21, 2013
            On Thu, Feb 21, 2013 at 05:46:26PM +0100, Erik Slagter wrote:

            > Another variation I tried ("pass" and "postscreen" the other way
            > around). This works, but gives the original problem, the smtpd
            > options are not honoured (especially banner and starttls="may"),
            > even though I set both:

            Take a DEEP breath, relax and don't *try* implementing new
            configurations you don't yet understand. The shots in the dark will
            just get you more confused.

            It is time to try to *understand*.

            1. A running Postfix instance is a collection of separate background
            services (daemons) launched by an inetd-like service supervisor known
            as "master. These services run independently in separate processes
            and communicate with each other using unix-domain sockets.

            They are configured either via main.cf (best practice) or via
            master.cf "-o parameter=$value" overrides (when you must).

            The MOST important thing you need to understand about this is:

            Adding "-o FOO=BAR" to the master.cf entry for SERVICEA has
            NO EFFECT on the value of FOO in SERVICEB!

            Even when the MESSAGE is passed from SERVICEA to SERVICEB the
            parameter settings ARE NOT.

            Thus when you convert an existing "smtpd" entry to a "postscreen"
            entry, it is a grave mistake to leave the "smtpd" (-o options)
            that tune the functionality of smtpd attached to the "postscreen"
            service. It (postscreen) won't care and the destination "smtpd"
            to which the message is handed off will no longer know the parameters.

            2. To provide multiple smtpd personalities, you need to implement multiple
            "smtpd" services each with their own settings. (As you do when smtpd
            listens directly on an "inet" socket).

            3. To implement 2. with postscreen, each "inet" listening postscreen
            (with settings relevant for postscreen) must hand the message off
            to an "smtpd" appropriate for its listening IP address.

            4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
            to hand the connection to. The postscreen(8) manual page refers you to

            http://www.postfix.org/postconf.5.html#smtpd_service_name

            which must specify the service name of a "pass" entry in master.cf,
            you need one of these for each distinct postscreen instance.

            192.0.2.1:25 inet ... postscreen
            -o smtpd_service_name=25@192.0.2.1
            -o <postscreen-related-settings> ...
            25@192.0.2.1 pass ... smtpd
            -o <smtpd-related-settings> ...

            Lather, rinse, repeat:

            192.0.2.1:587 inet ... postscreen
            -o smtpd_service_name=587@192.0.2.1
            -o <postscreen-related-settings> ...
            587@192.0.2.1 pass ... smtpd
            -o <smtpd-related-settings> ...

            Lather, rinse, repeat:

            192.0.2.2:25 inet ... postscreen
            -o smtpd_service_name=25@192.0.2.2
            -o <postscreen-related-settings> ...
            25@192.0.2.2 pass ... smtpd
            -o <smtpd-related-settings> ...

            Lather, rinse, repeat:

            192.0.2.3:25 inet ... postscreen
            -o smtpd_service_name=25@192.0.2.3
            -o <postscreen-related-settings> ...
            25@192.0.3.2 pass ... smtpd
            -o <smtpd-related-settings> ...

            ... but do stop eventually ... :-)

            --
            Viktor.
          • Erik Slagter
            ... And THAT is exactly the clue I was looking for! It works! The only thing that would have to be in the README file is the need to use smtpd service names
            Message 5 of 25 , Feb 22, 2013
              On 21-02-13 20:07, Viktor Dukhovni wrote:

              > [ ... ] (lot of patronising text removed)

              > 4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
              > to hand the connection to. The postscreen(8) manual page refers you to
              >
              > http://www.postfix.org/postconf.5.html#smtpd_service_name
              >
              > which must specify the service name of a "pass" entry in master.cf,
              > you need one of these for each distinct postscreen instance.

              And THAT is exactly the clue I was looking for! It works!

              The only thing that would have to be in the README file is the need to
              use "smtpd service names" in case of multiple smtp listeners, point to
              http://www.postfix.org/postconf.5.html#smtpd_service_name and then add a
              bit of really helpful text to the current one:

              "The internal service that postscreen(8) hands off allowed connections
              to. In a future version there may be different classes of SMTP service."

              If you google for this command, you'll get references to either this
              text or this thread :-(

              So for other people seeking to do the same, this does the trick, it's
              also simple once you know, the "service" parameter of a "pass" service
              is not an address:portno combo but an identifier:

              #
              # outside -> inside
              # postfix(25) -> amavis(10025)
              #

              mx1.ipv4.slagter.name:smtp inet n - n - 1 postscreen
              -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv4
              -o
              postscreen_greet_banner=mx1.slagter.name-ESMTP-mx1-postscreen-1-ppp0-ipv4-25
              -o smtpd_banner=mx1.slagter.name-ESMTP-mx1-postscreen-2-ppp0-ipv4-25
              -o postscreen_tls_security_level=none
              -o smtpd_service_name=mx1_ipv4

              mx1_ipv4 pass - - n - - smtpd
              -o myhostname=mx1.slagter.name
              -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv4-25
              -o smtpd_tls_security_level=may
              -o smtpd_proxy_filter=nemesis.ipv4:10025 # amavis

              mx1.ipv6.slagter.name:smtp inet n - n - 1 postscreen
              -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv6
              -o
              postscreen_greet_banner=mx1.slagter.name-ESMTP-mx1-postscreen-1-ppp0-ipv6-25
              -o smtpd_banner=mx1.slagter.name-ESMTP-mx1-postscreen-2-ppp0-ipv6-25
              -o postscreen_tls_security_level=none
              -o smtpd_service_name=mx1_ipv6

              mx1_ipv6 pass - - n - - smtpd
              -o myhostname=mx1.slagter.name
              -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv6-25
              -o smtpd_tls_security_level=may
              -o smtpd_proxy_filter=nemesis.ipv4:10025 # amavis
            • Viktor Dukhovni
              On Fri, Feb 22, 2013 at 11:04:34AM +0100, Erik Slagter wrote: First, a quick comment, all of the sturm and drang in this thread is the result of a peculiar
              Message 6 of 25 , Feb 22, 2013
                On Fri, Feb 22, 2013 at 11:04:34AM +0100, Erik Slagter wrote:

                First, a quick comment, all of the sturm and drang in this thread
                is the result of a peculiar reluctance of most users to heed the
                advice in MULTI_INSTANCE_README and simplify their configurations
                by handling each distinct message flow in a separate Postfix
                instance, each of which can be configured with few if any master.cf
                tweaks, and understood and maintained much more easily.

                A combination of MULTI_INSTANCE_README and POSTSCREEN_README would
                get you there much more quickly, and even allow simpler configuration
                of cases where identical policies apply to multiple protocol:address
                endpoints, since you can just set inet_interfaces in main.cf to list
                one or more network addresses for a given instance.

                I strongly recommend that you take the time to refactor your
                configuration to separate each flow into its own queue. The initial
                investment of time pays off quickly in easier to manage configurations
                and operational support (e.g. separate queues make it easier to
                see which flow is having problems).

                > On 21-02-13 20:07, Viktor Dukhovni wrote:
                >
                > > [ ... ] (lot of patronising text removed)

                Text that is required background knowledge to understand what
                follows, misconstrued to be patronizing rather than emphatic. Chill
                man, the blustery tone of this thread is mostly the result of your
                reticense to (AFAIK you never did) post the actual master.cf
                configuration that failed to meet your expectations. You should
                probably also not have included the text below in the initial post:

                The options (-o) that I specify on the various per-interface
                smtpd instances are NOT honoured anymore. ...

                Is this intentional? A know[n] bug? ...

                I must say the "howto" isn't very clear on this matter, it assumes you
                only have only one external interface.

                This is rude to the developers who take great pains to make Postfix
                unusually robust and well documented. The "patronising" text is
                sufficient to logically deduce that (and why) you need multiple
                smtpd "pass" services, at which point one looks for a parameter to
                specify the pass service, and finds it (in this case clustered
                sub-optimally with unrelated settings, we'll fix that) in the postscreen(8)
                manpage.

                If Wietse is still reading this, we should move "smtpd_service_name"
                to its ownn section nearer the top of the postscreen(8) manpage.

                Fortunately, the parameter name is just what you'd expect if you've
                ever seen "cleanup_service_name" which plays the same role one
                handoff downstream.

                > >4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
                > > to hand the connection to. The postscreen(8) manual page refers you to
                > >
                > > http://www.postfix.org/postconf.5.html#smtpd_service_name
                > >
                > > which must specify the service name of a "pass" entry in master.cf,
                > > you need one of these for each distinct postscreen instance.
                >
                > And THAT is exactly the clue I was looking for! It works!

                Naturally, since it is simply a logical consequence of understanding
                the patronising text. :-) Perhaps some people even spotted the
                transposition error in the last "Lather, rinse, repeat" example.
                (It has been observed that students pay more attention to technical
                books that contain minor errors that require them to pause and
                think, and that they learn more from these than from polished
                material that requires less attention).

                [
                Plus the fact that "unix" and "pass" service names are just file
                names in /var/spool/postfix/private/ which I started to describe
                in my first post, but decided to keep it more concise in the hope
                that this will be apparent from context.

                The master.cf services live in one of three namespaces:

                - inet/public (inet can't be private).

                - unix/public

                - unix/private

                Each of the "unix" cases subsumes "unix", "fifo" and "pass" since these
                all are accessed via paths in /var/spool/postfix/{public,private}.

                All delivery agents are "private" while "pickup", "qmgr", "flush"
                and "showq" are "public" to support postdrop(1) and postqueue(1)
                and their sendmail(1) interfaces. Almost everything else is private,
                except for cleanup(8) which AFAIK is public only for historical
                reasons.
                ]

                --
                Viktor.
              • Wietse Venema
                ... This was changed from private into public , so that postdrop could directly submit mail into cleanup, using the maildrop directory only as a fall-back
                Message 7 of 25 , Feb 22, 2013
                  Viktor Dukhovni:
                  > All delivery agents are "private" while "pickup", "qmgr", "flush"
                  > and "showq" are "public" to support postdrop(1) and postqueue(1)
                  > and their sendmail(1) interfaces. Almost everything else is private,
                  > except for cleanup(8) which AFAIK is public only for historical
                  > reasons.

                  This was changed from "private" into "public", so that postdrop
                  could directly submit mail into cleanup, using the maildrop directory
                  only as a fall-back mechanism in case cleanup transaction failed.
                  Recovering from all possible failure modes is complicated and I did
                  not get around to write that code (and there are few people who I
                  would trust to write it).

                  Wietse
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