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I am developing a firewall script for my server. So far it is working fine, except for FTP. Server is dedicated, CentOS based with static IP. There is no NAT between me and server. IPTables is a firewall.

Here is a script I use to configure iptables: http://pastebin.com/f54a70fec

I allow all RELATED and ESTABLISHED connections in it and load all conn_track modules. I supposed it to be sufficient in order FTP to work with iptables.

The problem is that FTP is not working either in passive or active mode. FileZilla and TotalCommander just hangs on MLSD FTP command. In the server log at the exact moment of FTP connection some weird packets are dropped by firewall:

Dec 20 15:37:09 server ntpd[12329]: synchronized to 81.200.8.213, stratum 5
Dec 20 15:37:14 server proftpd[30526]: gsmforum.ru (::ffff:95.24.7.25[::ffff:95.24.7.25]) - FTP session opened.
Dec 20 12:37:14 server proftpd[30526]: gsmforum.ru (::ffff:95.24.7.25[::ffff:95.24.7.25]) - Preparing to chroot to directory '/home/gsmforum'
Dec 20 15:37:23 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:1a:64:6b:1d:67:08:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=306 TOS=0x00 PREC=0x00 TTL=128 ID=32566 DF PROTO=UDP SPT=68 DPT=67 LEN=286
Dec 20 15:37:25 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:1f:29:63:03:de:08:00 SRC=89.111.189.17 DST=255.255.255.255 LEN=68 TOS=0x00 PREC=0x00 TTL=128 ID=13480 PROTO=UDP SPT=1052 DPT=1947 LEN=48
Dec 20 15:37:26 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=61798 PROTO=TCP SPT=4178 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:26 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:1a:64:9c:50:e7:08:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=306 TOS=0x00 PREC=0x00 TTL=128 ID=50015 DF PROTO=UDP SPT=68 DPT=67 LEN=286
Dec 20 15:37:26 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=62305 PROTO=TCP SPT=4178 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:26 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:19:bb:eb:c6:e1:08:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=30 ID=5245 PROTO=UDP SPT=68 DPT=67 LEN=308
Dec 20 15:37:27 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=63285 PROTO=TCP SPT=4178 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:29 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=391 PROTO=TCP SPT=4183 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:29 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=707 PROTO=TCP SPT=4178 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:30 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=975 PROTO=TCP SPT=4183 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:30 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:15:17:10:c5:9b:08:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=30 ID=28799 PROTO=UDP SPT=68 DPT=67 LEN=308
Dec 20 15:37:30 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=2020 PROTO=TCP SPT=4187 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:31 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=2383 PROTO=TCP SPT=4183 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:31 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=2533 PROTO=TCP SPT=4187 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:32 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=3271 PROTO=TCP SPT=4190 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:32 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=77.35.184.49 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=115 ID=14501 DF PROTO=TCP SPT=1355 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:32 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=3700 PROTO=TCP SPT=4187 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:32 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=3769 PROTO=TCP SPT=4196 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:32 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=4034 PROTO=TCP SPT=4190 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:33 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=4522 PROTO=TCP SPT=4196 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0
Dec 20 15:37:33 server kernel: {fw}UNKNOWN:IN=eth0 OUT= MAC=00:15:17:62:db:28:00:1f:26:27:34:c2:08:00 SRC=81.169.231.108 DST=79.174.68.223 LEN=40 TOS=0x00 PREC=0x00 TTL=53 ID=4657 PROTO=TCP SPT=4183 DPT=80 WINDOW=65535 RES=0x00 ACK FIN URGP=0

Can you please suggest what is the problem? Everything is working fine except for this damn FTP.

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BTW, no DHCP daemon is running on the system so I don't know where is this SPT=68 DPT=67 from. –  FractalizeR Dec 20 '09 at 12:42
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1 Answer 1

up vote 0 down vote accepted

The solution was to add

MasqueradeAddress example.com
PassivePorts 65400 65534

to /etc/proftpd.conf and configure iptables:

#FTP server(21)
iptables -A INPUT -p tcp -m tcp -i $FR_INET_IFACE --dport 21 -j ACCEPT #Main FTP port
iptables -A OUTPUT -p tcp -m tcp -o $FR_INET_IFACE --sport 20 -j ACCEPT #Active FTP port
iptables -A INPUT -p tcp -m tcp -i $FR_INET_IFACE --dport 65400:65534 -j ACCEPT #Passive FTP
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