1 .\" $OpenBSD: ftp-proxy.8,v 1.7 2006/12/30 13:01:54 camield Exp $
3 .\" Copyright (c) 2004, 2005 Camiel Dobbelaar, <cd@sentia.nl>
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24 .Nd Internet File Transfer Protocol proxy daemon
31 .Op Fl m Ar maxsessions
39 is a proxy for the Internet File Transfer Protocol.
40 FTP control connections should be redirected into the proxy using the
43 command, after which the proxy connects to the server on behalf of
46 The proxy allows data connections to pass, rewriting and redirecting
47 them so that the right addresses are used.
48 All connections from the client to the server have their source
49 address rewritten so they appear to come from the proxy.
50 Consequently, all connections from the server to the proxy have
51 their destination address rewritten, so they are redirected to the
58 Assuming the FTP control connection is from $client to $server, the
59 proxy connected to the server using the $proxy source address, and
60 $port is negotiated, then
62 adds the following rules to the various anchors.
63 (These example rules use inet, but the proxy also supports inet6.)
65 In case of active mode (PORT or EPRT):
66 .Bd -literal -offset 2n
67 rdr from $server to $proxy port $port -> $client
68 pass quick inet proto tcp \e
69 from $server to $client port $port
72 In case of passive mode (PASV or EPSV):
73 .Bd -literal -offset 2n
74 nat from $client to $server port $port -> $proxy
75 pass in quick inet proto tcp \e
76 from $client to $server port $port
77 pass out quick inet proto tcp \e
78 from $proxy to $server port $port
81 The options are as follows:
85 The proxy will expect and use IPv6 addresses for all communication.
86 Only the extended FTP modes EPSV and EPRT are allowed with IPv6.
87 The proxy is in IPv4 mode by default.
89 Only permit anonymous FTP connections.
90 Either user "ftp" or user "anonymous" is allowed.
92 The proxy will use this as the source address for the control
93 connection to a server.
95 Address where the proxy will listen for redirected control connections.
96 The default is 127.0.0.1, or ::1 in IPv6 mode.
98 Debug level, ranging from 0 to 7.
99 Higher is more verbose.
101 (These levels correspond to the
106 The process will stay in the foreground, logging to standard error.
107 .It Fl m Ar maxsessions
108 Maximum number of concurrent FTP sessions.
109 When the proxy reaches this limit, new connections are denied.
110 The default is 100 sessions.
111 The limit can be lowered to a minimum of 1, or raised to a maximum of 500.
114 Only used in combination with
116 The default is port 21.
118 Port where the proxy will listen for redirected connections.
119 The default is port 8021.
121 Create rules with queue
123 appended, so that data connections can be queued.
125 Fixed server address, also known as reverse mode.
126 The proxy will always connect to the same server, regardless of
127 where the client wanted to connect to (before it was redirected).
128 Use this option to proxy for a server behind NAT, or to forward all
129 connections to another proxy.
131 Rewrite sourceport to 20 in active mode to suit ancient clients that insist
132 on this RFC property.
134 Number of seconds that the control connection can be idle, before the
135 proxy will disconnect.
136 The maximum is 86400 seconds, which is also the default.
137 Do not set this too low, because the control connection is usually
138 idle when large data transfers are taking place.
140 Set the 'log' flag on pf rules committed by
142 Use twice to set the 'log-all' flag.
143 The pf rules do not log by default.
146 To make use of the proxy,
148 needs the following rules.
149 All anchors are mandatory.
150 Adjust the rules as needed.
153 .Bd -literal -offset 2n
154 nat-anchor "ftp-proxy/*"
155 rdr-anchor "ftp-proxy/*"
156 rdr pass on $int_if proto tcp from $lan to any port 21 -> \e
161 .Bd -literal -offset 2n
163 pass out proto tcp from $proxy to any port 21
171 does not allow the ruleset to be modified if the system is running at a
176 cannot add rules to the anchors and FTP data connections may get blocked.
178 Negotiated data connection ports below 1024 are not allowed.
180 The negotiated IP address for active modes is ignored for security
182 This makes third party file transfers impossible.
185 chroots to "/var/empty" and changes to user "proxy" to drop privileges.