FTP-PROXY(8)            OpenBSD System Manager's Manual           FTP-PROXY(8)

NAME
     ftp-proxy - Internet File Transfer Protocol proxy daemon

SYNOPSIS
     ftp-proxy [-6Adrv] [-a address] [-b address] [-D level] [-m maxsessions]
               [-P port] [-p port] [-q queue] [-R address] [-T tag]
               [-t timeout]

DESCRIPTION
     ftp-proxy is a proxy for the Internet File Transfer Protocol.  FTP con-
     trol connections should be redirected into the proxy using the pf(4) rdr-
     to command, after which the proxy connects to the server on behalf of the
     client.

     The proxy allows data connections to pass, rewriting and redirecting them
     so that the right addresses are used.  All connections from the client to
     the server have their source address rewritten so they appear to come
     from the proxy.  Consequently, all connections from the server to the
     proxy have their destination address rewritten, so they are redirected to
     the client.  The proxy uses the pf(4) anchor facility for this.

     Assuming the FTP control connection is from $client to $server, the proxy
     connected to the server using the $proxy source address, and $port is ne-
     gotiated, then ftp-proxy adds the following rules to the anchor.  $server
     and $orig_server are the same unless -R is used to force a different
     $server address for all connections.  (These example rules use inet, but
     the proxy also supports inet6.)

     In case of active mode (PORT or EPRT):

       pass in from $server to $proxy port $proxy_port \
           rdr-to $client port $port
       pass out from $server to $client port $port \
           nat-to $orig_server port $natport

     In case of passive mode (PASV or EPSV):

       pass in from $client to $orig_server port $proxy_port \
           rdr-to $server port $port
       pass out from $client to $server port $port nat-to $proxy

     The options are as follows:

     -6      IPv6 mode.  The proxy will expect and use IPv6 addresses for all
             communication.  Only the extended FTP modes EPSV and EPRT are al-
             lowed with IPv6.  The proxy is in IPv4 mode by default.

     -A      Only permit anonymous FTP connections.  Either user "ftp" or user
             "anonymous" is allowed.

     -a address
             The proxy will use this as the source address for the control
             connection to a server.

     -b address
             Address where the proxy will listen for redirected control con-
             nections.  The default is 127.0.0.1, or ::1 in IPv6 mode.

     -D level
             Debug level, ranging from 0 to 7.  Higher is more verbose.  The
             default is 5.  (These levels correspond to the syslog(3) levels.)

     -d      Do not daemonize.  The process will stay in the foreground, log-
             ging to standard error.

     -m maxsessions
             Maximum number of concurrent FTP sessions.  When the proxy reach-
             es this limit, new connections are denied.  The default is 100
             sessions.  The limit can be lowered to a minimum of 1, or raised
             to a maximum of 500.

     -P port
             Fixed server port.  Only used in combination with -R.  The de-
             fault is port 21.

     -p port
             Port where the proxy will listen for redirected connections.  The
             default is port 8021.

     -q queue
             Create rules with queue queue appended, so that data connections
             can be queued.

     -R address
             Fixed server address, also known as reverse mode.  The proxy will
             always connect to the same server, regardless of where the client
             wanted to connect to (before it was redirected).  Use this option
             to proxy for a server behind NAT, or to forward all connections
             to another proxy.

     -r      Rewrite sourceport to 20 in active mode to suit ancient clients
             that insist on this RFC property.

     -T tag  The filter rules will add tag tag to data connections, and will
             use match rules instead of pass ones.  This way alternative rules
             that use the tagged keyword can be implemented following the ftp-
             proxy anchor.  These rules can use special pf(4) features like
             route-to, reply-to, label, rtable, overload, etc. that ftp-proxy
             does not implement itself.  There must be a matching pass rule
             after the ftp-proxy anchor or the data connections will be
             blocked.

     -t timeout
             Number of seconds that the control connection can be idle, before
             the proxy will disconnect.  The maximum is 86400 seconds, which
             is also the default.  Do not set this too low, because the con-
             trol connection is usually idle when large data transfers are
             taking place.

     -v      Set the 'log' flag on pf rules committed by ftp-proxy.  Use twice
             to set the 'log-all' flag.  The pf rules do not log by default.

CONFIGURATION
     To make use of the proxy, pf.conf(5) needs the following rules.  Adjust
     the rules as needed.

       anchor "ftp-proxy/*"
       pass in quick proto tcp to port ftp rdr-to 127.0.0.1 port 8021

SEE ALSO
     ftp(1), pf(4), pf.conf(5)

CAVEATS
     pf(4) does not allow the ruleset to be modified if the system is running
     at a securelevel(7) higher than 1.  At that level ftp-proxy cannot add
     rules to the anchors and FTP data connections may get blocked.

     Negotiated data connection ports below 1024 are not allowed.

     The negotiated IP address for active modes is ignored for security rea-
     sons.  This makes third party file transfers impossible.

     ftp-proxy chroots to "/var/empty" and changes to user "proxy" to drop
     privileges.

OpenBSD 4.7                    November 21, 2009                             3
