IPtables settings to access a backup FTP

Hello, this is my first message so I hope I'm doing this right ! :)

I've got iptables setup and running well on my server and up to now I've not had any problems, however I have just installed a backup system which needs to connect by FTP to a distant server.

With my firewall disactivated all works fine, however with the firewall activated when I use the "ls" command of the debian ftp command line package (CWD) I get:

200 ok then a long wait then :
421 Service not available, remote server has closed connection.

I've tried this on two different FTP's and it only works if the firewall is disactivated.

One server is a plesk server but the server I need to connect to I do not know much about, with filezilla on my pc I've managed to connect to it with both FTP active and FTP passive so I guess it can do both.

On my server I just do :

ftp ftp.server.com
username
password

So I'm not sure if it connects as passive or active.

These are the ports that I have got open :

-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

-A INPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 21 -j ACCEPT

-A OUTPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 21 -j ACCEPT

Which ports do you suggest I should open to connect to this FTP server ?

Thanks in advance,

Richard

Do you also want to accept FTP connections? You don't need this to make outgoing connections.

This is nonsense.

This is the only rule you need to make outgoing FTP connections.

It's not only about static ports. FTP uses dynamic ports as well that must be tracked by a helper. Modprobe nf_contrack_ftp (ip_contrack_ftp on older kernels) and all should be well.

HTH,
M4

Hi I've got ip_conntrack running,

My server hosts FTP accounts and I also need outgoing ftp ...

No problems accessing the ftp hosted on this server, but can't do a CWD (ls) from this server to another external ftp server unless the firewall is disactivated.

I guess you are going to say most of my settings are useless but here goes my current settings :

-------------------------

Chain INPUT (policy DROP)

target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTAB 
                  LISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp-data
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp
LOG_ACCEPT  tcp  --  anywhere             anywhere            tcp dpt:2022
LOG_ACCEPT  tcp  --  anywhere             anywhere            tcp dpt:smtp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:whois
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:imap2
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:https
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ntp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:8443
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:8880
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:42630
ACCEPT     udp  --  anywhere             anywhere            udp dpt:42630
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:imaps
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:mysql
ACCEPT     all  --  localhost.localdomain  anywhere

icmp_packets icmp -- anywhere anywhere
LOG_DROP all -- anywhere anywhere

Chain FORWARD (policy DROP)

target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp flags:S 

YN,RST,ACK/SYN

Chain OUTPUT (policy DROP)

target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTAB 
                  LISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp-data
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:2022
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:telnet
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:smtp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:whois
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:www
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:imap2
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:https
ACCEPT     udp  --  anywhere             anywhere            udp dpt:ntp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:imaps
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:mysql
ACCEPT     all  --  anywhere             localhost.localdomain

icmp_packets icmp -- anywhere anywhere
LOG_DROP all -- anywhere anywhere

Chain LOG_ACCEPT (2 references)

target     prot opt source               destination
LOG        all  --  anywhere             anywhere            LOG level warning t 

cp-options ip-options prefix `[IPTABLES ACCEPT] : '
ACCEPT all -- anywhere anywhere

Chain LOG_DROP (2 references)

target     prot opt source               destination
LOG        all  --  anywhere             anywhere            LOG level warning t 

cp-options ip-options prefix `[IPTABLES DROP] : '
DROP all -- anywhere anywhere

Chain icmp_packets (2 references)

target     prot opt source               destination
ACCEPT     icmp --  anywhere             anywhere            limit: avg 1/sec bu 

rst 1
LOG icmp -- anywhere anywhere limit: avg 1/sec bu
rst 1 LOG level warning prefix `PING-DROP: '

--------------

Thanks for any suggestions !

Richard

Richard wrote:

[ Please don't toppost. Thanks ]

I was talking about ip_conntrack_ftp, not ip_conntrack. You need both. The difference is between ftp working and not working at the first LS command.

Clear, so you need the input rule on port 21 as well.

No problems? Impossible with the rules you posted.

Thanks, but that is virtually unreadable. Post the output of iptables-save instead.

HTH,
M4

Thankyou ! That fixed my problem ! I did a lsmod and it was not there so I did a mprobe ip_conntrack_ftp and then added ip_conntrack_ftp to /etc/modules

Now my backup system works well !

Now for my iptable settings, here is my file :

------

#The NAT portion of the ruleset. Used for Network Address Transalation. #Usually not needed on a typical web server, but it's there if you need it. *nat
:PREROUTING ACCEPT [127173:7033011]
:POSTROUTING ACCEPT [31583:2332178]
:OUTPUT ACCEPT [32021:2375633]
COMMIT

#The Mangle portion of the ruleset. Here is where unwanted packet types get dropped.
#This helps in making port scans against your server a bit more time consuming and difficult, but not impossible. *mangle
:PREROUTING ACCEPT [444:43563]
:INPUT ACCEPT [444:43563]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [402:144198]
:POSTROUTING ACCEPT [402:144198]
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PREROUTING -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
COMMIT

#The FILTER section of the ruleset is where we initially drop all packets and then selectively open certain ports. #We will also enable logging of all dropped requests.
*filter
:INPUT DROP [1:242]
:FORWARD DROP [0:0]
:OUTPUT DROP [0:0]
:LOG_DROP - [0:0]
:LOG_ACCEPT - [0:0]
:icmp_packets - [0:0]

#test
-A FORWARD -i eth0 -o eth1 -p tcp --syn --dport 21 -j ACCEPT #First, we cover the INPUT rules, or the rules for incoming requests. #Note how at the end we log any incoming packets that are not accepted. -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 21 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 2022 -j LOG_ACCEPT
-A INPUT -p tcp -m tcp --dport 25 -j LOG_ACCEPT
-A INPUT -p tcp -m tcp --dport 43 -j ACCEPT
-A INPUT -p udp -m udp --dport 53 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 110 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 123 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 8443 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 8880 -j ACCEPT
#Passive FTP connections
-A INPUT -p tcp -m tcp --dport 32876 -j ACCEPT
-A INPUT -p udp -m udp --dport 32876 -j ACCEPT

#uncomment the next line if you are running Spamassassin on your server #-A INPUT -p tcp -m tcp --dport 783 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 993 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 3306 -j ACCEPT
-A INPUT -s 127.0.0.1 -j ACCEPT
-A INPUT -p icmp -j icmp_packets
-A INPUT -j LOG_DROP

#Next, we cover the OUTPUT rules, or the rules for all outgoing traffic. #Note how at the end we log any outbound packets that are not accepted. -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 21 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 2022 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 23 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 25 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 43 -j ACCEPT
-A OUTPUT -p udp -m udp --dport 53 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 110 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 143 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A OUTPUT -p udp -m udp --dport 123 -j ACCEPT
#uncomment the next line if you are running Spamassassin on your server #-A OUTPUT -p tcp -m tcp --dport 783 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 993 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 3306 -j ACCEPT
-A OUTPUT -d 127.0.0.1 -j ACCEPT
-A OUTPUT -p icmp -j icmp_packets
-A OUTPUT -j LOG_DROP

#Here we have 2 sets of logging rules. One for dropped packets to log all dropped requests and one for accepted packets, should we wish to log any accepted requesets. -A LOG_DROP -j LOG --log-prefix "[IPTABLES DROP] : " --log-tcp-options --log-ip-options
-A LOG_DROP -j DROP

-A LOG_ACCEPT -j LOG --log-prefix "[IPTABLES ACCEPT] : " --log-tcp-options --log-ip-options -A LOG_ACCEPT -j ACCEPT

#And finally, a rule to deal with ICMP requests. We drop all ping requests except from our own server. # Make sure you replace 1.2.3.4 with the IP address of your server.
#-A icmp_packets -p icmp -m icmp --icmp-type 0 -j ACCEPT
#-A icmp_packets -p icmp -m icmp --icmp-type 8 -j ACCEPT
#-A icmp_packets -p icmp -m icmp --icmp-type 3 -j ACCEPT
#-A icmp_packets -p icmp -m icmp --icmp-type 11 -j ACCEPT
-A icmp_packets -p icmp -m limit --limit 1/s --limit-burst 1 -j ACCEPT
-A icmp_packets -p icmp -m limit --limit 1/s --limit-burst 1 -j LOG --log-prefix "PING-DROP: "

COMMIT

-----

So as far as I understand, I must remove the two following lines :

-A INPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 20 -j ACCEPT

Thanks again !

Richard