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ANVIL(8)                                                                                            ANVIL(8)



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 request
       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 configurable 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  (ser-vice, (service,
       vice, 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 (ser-vice, (service,
       vice, client) combination specified with ident:

           status=0
           rate=number

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

           request=newtls_report
           ident=string

       The anvil(8) server answers with the number of new TLS session requests per unit time for  the  (ser-vice, (service,
       vice, 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 requests.   No
       persistent  state  is  kept  because standard system library routines are not sufficiently 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).

       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 associated 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) processes 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 exam-ples. examples.
       ples.

       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 information.

       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 terminated 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 connec-tion connection
              tion 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)
              The  mail system name that is prepended to the process name in syslog records, so that "smtpd"
              becomes, for example, "postfix/smtpd".

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



                                                                                                    ANVIL(8)