Provided by: postfix_3.0.4-5build1_i386 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

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

                                                               ANVIL(8postfix)