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ANVIL(8postfix)                                                                      ANVIL(8postfix)



NAME
       anvil - Postfix session count and request rate control

SYNOPSIS
       anvil [generic Postfix daemon options]

DESCRIPTION
       The Postfix anvil(8) server maintains statistics about client connection counts or client re‐
       quest rates. This information can be used to defend against clients that hammer a server with
       either  too many simultaneous sessions, or with too many successive requests within a config‐
       urable time interval.  This server is designed to run under control by the Postfix  master(8)
       server.

       In  the  following text, ident specifies a (service, client) combination. The exact syntax of
       that information is application-dependent; the anvil(8) server does not care.

CONNECTION COUNT/RATE CONTROL
       To register a new connection send the following request to the anvil(8) server:

           request=connect
           ident=string

       The anvil(8) server answers with the number of simultaneous connections  and  the  number  of
       connections per unit time for the (service, client) combination specified with ident:

           status=0
           count=number
           rate=number

       To register a disconnect event send the following request to the anvil(8) server:

           request=disconnect
           ident=string

       The anvil(8) server replies with:

           status=0

MESSAGE RATE CONTROL
       To register a message delivery request send the following request to the anvil(8) server:

           request=message
           ident=string

       The  anvil(8)  server  answers with the number of message delivery requests per unit time for
       the (service, client) combination specified with ident:

           status=0
           rate=number

RECIPIENT RATE CONTROL
       To register a recipient request send the following request to the anvil(8) server:

           request=recipient
           ident=string

       The anvil(8) server answers with the number of recipient addresses  per  unit  time  for  the
       (service, client) combination specified with ident:

           status=0
           rate=number

TLS SESSION NEGOTIATION RATE CONTROL
       The features described in this section are available with Postfix 2.3 and later.

       To  register  a request for a new (i.e. not cached) TLS session send the following request to
       the anvil(8) server:

           request=newtls
           ident=string

       The anvil(8) server answers with the number of new TLS session requests per unit time for the
       (service, client) combination specified with ident:

           status=0
           rate=number

       To  retrieve  new  TLS session request rate information without updating the counter informa‐
       tion, send:

           request=newtls_report
           ident=string

       The anvil(8) server answers with the number of new TLS session requests per unit time for the
       (service, client) combination specified with ident:

           status=0
           rate=number

AUTH RATE CONTROL
       To register an AUTH request send the following request to the anvil(8) server:

           request=auth
           ident=string

       The  anvil(8) server answers with the number of auth requests per unit time for the (service,
       client) combination specified with ident:

           status=0
           rate=number

SECURITY
       The anvil(8) server does not talk to the network or to local users, and can run  chrooted  at
       fixed low privilege.

       The  anvil(8)  server  maintains an in-memory table with information about recent clients re‐
       quests.  No persistent state is kept because standard system library routines are not  suffi‐
       ciently robust for update-intensive applications.

       Although  the  in-memory  state is kept only temporarily, this may require a lot of memory on
       systems that handle connections from many remote clients.  To reduce memory usage, reduce the
       time unit over which state is kept.

DIAGNOSTICS
       Problems and transactions are logged to syslogd(8) or postlogd(8).

       Upon  exit, and every anvil_status_update_time seconds, the server logs the maximal count and
       rate values measured, together with (service, client) information and the time of day associ‐
       ated with those events.  In order to avoid unnecessary overhead, no measurements are done for
       activity that isn't concurrency limited or rate limited.

BUGS
       Systems behind network address translating routers or proxies appear to have the same  client
       address and can run into connection count and/or rate limits falsely.

       In  this  preliminary  implementation, a count (or rate) limited server process can have only
       one remote client at a time. If a server process reports multiple simultaneous clients, state
       is kept only for the last reported client.

       The  anvil(8)  server automatically discards client request information after it expires.  To
       prevent the anvil(8) server from discarding client request rate information too early or  too
       late,  a  rate  limited service should always register connect/disconnect events even when it
       does not explicitly limit them.

CONFIGURATION PARAMETERS
       On low-traffic mail systems, changes to main.cf are picked up automatically as anvil(8)  pro‐
       cesses run for only a limited amount of time. On other mail systems, use the command "postfix
       reload" to speed up a change.

       The text below provides only a parameter summary. See postconf(5) for more details  including
       examples.

       anvil_rate_time_unit (60s)
              The time unit over which client connection rates and other rates are calculated.

       anvil_status_update_time (600s)
              How frequently the anvil(8) connection and rate limiting server logs peak usage infor‐
              mation.

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf configuration files.

       daemon_timeout (18000s)
              How much time a Postfix daemon process may take to handle a request before it is  ter‐
              minated by a built-in watchdog timer.

       ipc_timeout (3600s)
              The  time  limit  for  sending or receiving information over an internal communication
              channel.

       max_idle (100s)
              The maximum amount of time that an idle Postfix daemon process waits for  an  incoming
              connection before terminating voluntarily.

       max_use (100)
              The  maximal number of incoming connections that a Postfix daemon process will service
              before terminating voluntarily.

       process_id (read-only)
              The process ID of a Postfix command or daemon process.

       process_name (read-only)
              The process name of a Postfix command or daemon process.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A prefix that is prepended to the process name in syslog records, so that,  for  exam‐
              ple, "smtpd" becomes "prefix/smtpd".

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

SEE ALSO
       smtpd(8), Postfix SMTP server
       postconf(5), configuration parameters
       master(5), generic daemon options

README FILES
       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       TUNING_README, performance tuning

LICENSE
       The Secure Mailer license must be distributed with this software.

HISTORY
       The anvil service is available in Postfix 2.2 and later.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA



                                                                                     ANVIL(8postfix)