Provided by: postfix_3.1.0-3_amd64 bug

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
       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

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
       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 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

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

                                                                                  ANVIL(8postfix)