From 74de3e775faebab29e4d3f12cc9dbc012197e431 Mon Sep 17 00:00:00 2001 From: mhnoyes Date: Mon, 15 Dec 2003 18:06:49 +0000 Subject: [PATCH] Content moved to FTP.xml git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@854 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb --- Shorewall-docs/FTP.html | 243 ---------------------------------------- 1 file changed, 243 deletions(-) delete mode 100644 Shorewall-docs/FTP.html diff --git a/Shorewall-docs/FTP.html b/Shorewall-docs/FTP.html deleted file mode 100644 index f1291a564..000000000 --- a/Shorewall-docs/FTP.html +++ /dev/null @@ -1,243 +0,0 @@ - - - - - Shorewall and FTP - - - - -

-
-

Shorewall and FTP
-

-
-

NOTICE: If you are running -Mandrake 9.1 or 9.2 and are having problems with FTP, you have three -choices:

-
    -
  1. Edit /usr/share/shorewall/firewall and replace this line:
    -
    -   for suffix in o gz ko ; do
    -
    -with
    -
    -   for suffix in o gz ko o.gz ; do
    -
    -     and at a root shell prompt:
    -
    -  shorewall -restart
    -
    -
    2. -
  2. Install the Mandrake "cooker" version of Shorewall.
    -
    -
    3. -
  3. Upgrade to Shorewall 1.4.7 or later.
    -
    4. -
-
-

FTP transfers involve two TCP connections. The first control -connection goes from the FTP client to port 21 on the FTP server. This -connection is used for logon and to send commands and responses between -the endpoints. Data transfers (including the output of "ls" and "dir" -commands) requires a second data connection. The data -connection is dependent on the mode -that the client is operating in:
-

- -You can see these commands in action using your linux ftp command-line -client in debugging mode. Note that my ftp client defaults to passive -mode and that I can toggle between passive and active mode by issuing a -"passive" command:
-
- 
[teastep@wookie Shorewall]$ ftp ftp1.shorewall.net
Connected to lists.shorewall.net.
220-=(<*>)=-.:. (( Welcome to PureFTPd 1.0.12 )) .:.-=(<*>)=-
220-You are user number 1 of 50 allowed.
220-Local time is now 10:21 and the load is 0.14. Server port: 21.
220 You will be disconnected after 15 minutes of inactivity.
500 Security extensions not implemented
500 Security extensions not implemented
KERBEROS_V4 rejected as an authentication type
Name (ftp1.shorewall.net:teastep): ftp
331-Welcome to ftp.shorewall.net
331-
331 Any password will work
Password:
230 Any password will work
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> debug
Debugging on (debug=1).
ftp> ls
---> PASV
227 Entering Passive Mode (192,168,1,193,195,210)
---> LIST
150 Accepted data connection
drwxr-xr-x    5 0        0            4096 Nov  9  2002 archives
drwxr-xr-x    2 0        0            4096 Feb 12  2002 etc
drwxr-sr-x    6 0        50           4096 Feb 19 15:24 pub
226-Options: -l
226 3 matches total
ftp> passive
Passive mode off.
ftp> ls
---> PORT 192,168,1,3,142,58
200 PORT command successful
---> LIST
150 Connecting to port 36410
drwxr-xr-x    5 0        0            4096 Nov  9  2002 archives
drwxr-xr-x    2 0        0            4096 Feb 12  2002 etc
drwxr-sr-x    6 0        50           4096 Feb 19 15:24 pub
226-Options: -l
226 3 matches total
ftp>
-
-Things to notice:
-
    -
  1. The commands that I issued are in green.
    -
    2. -
  2. Commands sent by the client to the server are preceded by --->
    3. -
  3. Command responses from the server over the control connection are -numbered.
    -
    4. -
  4. FTP uses a comma as a separator between the bytes of the IP -address; and
    5. -
  5. When sending a port number, FTP sends the MSB then the LSB and -separates the two bytes by a comma. As shown in the PORT command, port -142,58 translates -to 142*256+58 = 36410.
    -
    6. -
-Given the normal loc->net policy of ACCEPT, passive mode access from -local clients to remote servers will always work but active mode -requires the firewall to dynamically open a "hole" for the server's -connection back to the client. Similarly, if you are running an FTP -server in your local -zone then active mode should always work but passive mode requires the -firewall to dynamically open a "hole" for the client's second -connection to the server. This is the role of FTP connection-tracking -support in the Linux kernel. -

-Where any form of NAT (SNAT, DNAT, Masquerading) on your firewall is -involved, the PORT commands and PASV responses may also need to be -modified by the firewall. This is the job of the FTP nat support kernel -function.
-
-

Including FTP connection-tracking and NAT support normally means -that the -modules "ip_conntrack_ftp" and "ip_nat_ftp" need to be loaded. -Shorewall automatically -loads these "helper" modules from /lib/modules/<kernel-version>/kernel/net/ipv4/netfilter/ -and you can determine if they are loaded using the 'lsmod' command. The -<kernel-version> may be -obtained by typing
-

-
	uname -r
-
-Example:
-
-
- 
[root@lists etc]# lsmod
Module                  Size  Used by    Not tainted
autofs                 12148   0  (autoclean) (unused)
ipt_TOS                 1560  12  (autoclean)
ipt_LOG                 4120   5  (autoclean)
ipt_REDIRECT            1304   1  (autoclean)
ipt_REJECT              3736   4  (autoclean)
ipt_state               1048  13  (autoclean)
ip_nat_irc              3152   0  (unused)
ip_nat_ftp              3888   0  (unused)
ip_conntrack_irc        3984   1
ip_conntrack_ftp        5008   1
ipt_multiport           1144   2  (autoclean)
ipt_conntrack           1592   0  (autoclean)
iptable_filter          2316   1  (autoclean)
iptable_mangle          2680   1  (autoclean)
iptable_nat            20568   3  (autoclean) [ipt_REDIRECT ip_nat_irc ip_nat_ftp]
ip_conntrack           26088   5  (autoclean) [ipt_REDIRECT ipt_state ip_nat_irc
					      ip_nat_ftp ip_conntrack_irc ip_conntrack_ftp
                                              ipt_conntrack iptable_nat]
ip_tables              14488  12  [ipt_TOS ipt_LOG ipt_REDIRECT ipt_REJECT ipt_state
                                  ipt_multiport ipt_conntrack iptable_filter
                                  iptable_mangle iptable_nat]
tulip                  42464   0  (unused)
e100                   50596   1
keybdev                 2752   0  (unused)
mousedev                5236   0  (unused)
hid                    20868   0  (unused)
input                   5632   0  [keybdev mousedev hid]
usb-uhci               24684   0  (unused)
usbcore                73280   1  [hid usb-uhci]
ext3                   64704   2
jbd                    47860   2  [ext3]
[root@lists etc]#
-
-
-
-

If you want Shorewall to load these modules from an alternate -directory, you need to set the MODULESDIR variable in -/etc/shorewall/shorewall.conf to point to that directory.
-

-

If your FTP helper modules are compressed and have the names ip_nat_ftp.o.gz and ip_conntrack_ftp.o.gz then you will -need Shorewall 1.4.7 or later if you want Shorewall to load them for -you.
-

-

Server configuration is covered in the -/etc/shorewall/rules documentation,
-

-

For a client, you must open outbound TCP port 21. 
-

-

The above discussion about commands and responses makes it clear -that the -FTP connection-tracking and NAT helpers must scan the traffic on the -control -connection looking for PASV and PORT commands as well as PASV -responses. If -you run an FTP server on a nonstandard port or you need to access such -a server,  you must therefore let the helpers know by specifying -the port -in /etc/shorewall/modules entries for the helpers. For example, if you -run an FTP server that listens on port 49 or you need to access a -server on the internet that listens on that port then you would have:
-

-
-

loadmodule ip_conntrack_ftp ports=21,49
-loadmodule ip_nat_ftp ports=21,49
-

-
-

Note that you MUST include port 21 in the ports list or you -may have problems accessing regular FTP servers.

-

If there is a possibility that these modules might be loaded before -Shorewall starts, then you should include the port list in -/etc/modules.conf:
-

-
-

options ip_conntrack_ftp ports=21,49
-options ip_nat_ftp ports=21,49
-

-
-

IMPORTANT: Once you have made these changes to -/etc/shorewall/modules and/or /etc/modules.conf, you must either:
-

-
    -
  1. Unload the modules and restart shorewall: (rmmod ip_nat_ftp; rmmod ip_conntrack_ftp; shorewall -restart); or
    2. -
  2. Reboot
    3. -
-One problem that I see occasionally involves active mode and the FTP -server in my DMZ. I see the active data connection to certain -client IP addresses being continuously rejected by my firewall. It -is my conjecture that there is some broken client out there that is -sending a PORT command that is being either missed or mis-interpreted -by the FTP connection tracking helper yet it is being accepted by my -FTP server. My solution is to add the following rule:
-
- - - - - - - - - - - - - - - - - - - - - -
ACTION
- 		SOURCE
- 		DESTINATION
- 		PROTOCOL
- 		PORT(S)
- 		SOURCE
-PORT(S)
- 		ORIGINAL
-DESTINATION
-
ACCEPT:info
- 		dmz
- 		net
- 		tcp
- 		-
- 		20
-
-
-
-
-The above rule accepts and logs all active mode connections from my DMZ -to the net.
-
-

-
-
-

Last updated 12/01/2003 - Tom Eastep

-Copyright © 2003 Thomas M. Eastep.
-
-
-
- -