ANVIL(8)						      System Manager's Manual							  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  con-
       figurable 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 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 (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 stan-
       dard 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 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 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)
	      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)