ftp-proxy man page on FreeBSD

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

     ftp-proxy — Internet File Transfer Protocol proxy daemon

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

     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
     command, after which the proxy connects to the server on behalf of the

     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
     negotiated, then ftp-proxy adds the following rules to the various
     anchors.  (These example rules use inet, but the proxy also supports

     In case of active mode (PORT or EPRT):

       rdr from $server to $proxy port $port -> $client
       pass quick inet proto tcp \
	   from $server to $client port $port

     In case of passive mode (PASV or EPSV):

       nat from $client to $server port $port -> $proxy
       pass in quick inet proto tcp \
	   from $client to $server port $port
       pass out quick inet proto tcp \
	   from $proxy to $server port $port

     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
	     allowed 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, 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
	     reaches 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
	     default 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 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.

     To make use of the proxy, pf.conf(5) needs the following rules.  All
     anchors are mandatory.  Adjust the rules as needed.

     In the NAT section:

       nat-anchor "ftp-proxy/*"
       rdr-anchor "ftp-proxy/*"
       rdr pass on $int_if proto tcp from $lan to any port 21 -> \ port 8021

     In the rule section:

       anchor "ftp-proxy/*"
       pass out proto tcp from $proxy to any port 21

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

     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

BSD			       November 28, 2004			   BSD

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