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 connec-
       tion counts or client request rates. This information can  be  used  to
       defend against clients that hammer a server with either too many simul-
       taneous sessions, or with too many successive requests within a config-
       urable  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-inten-
       sive 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
       can have only one remote client at a time. If a server 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 automati-
       cally  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  con-
              figuration 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 (postfix)
              The mail system name that is prepended to the  process  name  in
              syslog  records,  so  that  "smtpd" becomes, for example, "post-
              fix/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)
