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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
       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 (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

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 includ-
       ing 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
	      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 incom-
	      ing connection before terminating voluntarily.

       max_use(100)
	      The maximal number of incoming connections that a Postfix daemon process will  ser-
	      vice 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(8postfix)
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