[NTLUG:Discuss] ftp problems through firewall

Thu Feb 28 22:19:50 CST 2002

Try allowing port 20 through the firewall in addition to 21.  If that
does not work, try running ftp in passive mode.

On Thu, 2002-02-28 at 20:59, Raymond Norton wrote:
> I have an iptable script running on my RedHat 7.1 box. It works great
> running my laptop through it for everything except when I try to access ftp
> servers on the outside. I am able to connect, but I cannot issue any
> commands with out getting an error: "Cannot connect to (outside
> interface):1294"
> 
> Any ideas how to resolve this? I have attached the script as I run it.
> -- 
> Raymond Norton
> Little Crow Telemedia Network
> 320-234-0270
> 
> ----
> 

> #!/bin/sh
> #
> # rc.firewall - Initial SIMPLE IP Firewall script for Linux 2.4.x and iptables
> #
> # Copyright (C) 2001  Oskar Andreasson &lt;blueflux at koffein.net&gt;
> #
> # This program is free software; you can redistribute it and/or modify
> # it under the terms of the GNU General Public License as published by
> # the Free Software Foundation; version 2 of the License.
> #
> # This program is distributed in the hope that it will be useful,
> # but WITHOUT ANY WARRANTY; without even the implied warranty of
> # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> # GNU General Public License for more details.
> #
> # You should have received a copy of the GNU General Public License
> # along with this program or from the site that you downloaded it
> # from; if not, write to the Free Software Foundation, Inc., 59 Temple
> # Place, Suite 330, Boston, MA  02111-1307   USA
> #
> 
> ###########################################################################
> #
> # 1. Configuration options.
> #
> 
> ###########################################################################
> #
> # Local Area Network configuration.
> #
> # your LAN's IP range and localhost IP. /24 means to only use the first 24 
> # bits of the 32 bit IP adress. the same as netmask 255.255.255.0
> #
> 
> LAN_IP="192.168.0.1"
> LAN_IP_RANGE="192.168.0.0/24"
> LAN_BCAST_ADRESS="192.168.255.255"
> LAN_IFACE="eth1"
> 
> ###########################################################################
> #
> # Localhost Configuration.
> #
> 
> LO_IFACE="lo"
> LO_IP="127.0.0.1"
> 
> ###########################################################################
> #
> # Internet Configuration.
> #
> 
> INET_IP=""
> INET_IFACE="eth0"
> 
> ###########################################################################
> #
> # IPTables Configuration.
> #
> 
> IPTABLES="/sbin/iptables"
> 
> ###########################################################################
> #
> # 2. Module loading.
> #
> 
> #
> # Needed to initially load modules
> #
> /sbin/depmod -a
> 
> #
> # Adds some iptables targets like LOG, REJECT and MASQUARADE.
> #
> /sbin/modprobe ip_conntrack
> /sbin/modprobe ip_tables
> /sbin/modprobe iptable_filter
> /sbin/modprobe iptable_mangle
> /sbin/modprobe iptable_nat
> /sbin/modprobe ipt_LOG
> #/sbin/modprobe ipt_REJECT
> #/sbin/modprobe ipt_MASQUERADE
> 
> #
> # Support for owner matching
> #
> #/sbin/modprobe ipt_owner
> 
> #
> # Support for connection tracking of FTP and IRC.
> #
> /sbin/modprobe ip_conntrack_ftp
> /sbin/modprobe ip_conntrack_irc
> 
> 
> ###########################################################################
> #
> # 3. /proc set up.
> #
> # Enable ip_forward if you have two or more networks, including the
> # Internet, that needs forwarding of packets through this box. This is
> # critical since it is turned off as default in Linux.
> #
> 
> echo "1" > /proc/sys/net/ipv4/ip_forward
> 
> #
> # Dynamic IP users:
> #
> #echo "1" > /proc/sys/net/ipv4/ip_dynaddr
> 
> ###########################################################################
> #
> # 4. IPTables rules set up.
> #
> # Set default policies for the INPUT, FORWARD and OUTPUT chains.
> #
> 
> $IPTABLES -P INPUT DROP
> $IPTABLES -P OUTPUT DROP
> $IPTABLES -P FORWARD DROP
> 
> #
> # bad_tcp_packets chain
> #
> # Take care of bad TCP packets that we don't want.
> #
> 
> $IPTABLES -N bad_tcp_packets
> $IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG \
> --log-prefix "New not syn:"
> $IPTABLES -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP
> 
> #
> # Do some checks for obviously spoofed IP's
> #
> 
> $IPTABLES -A bad_tcp_packets -i $INET_IFACE -s 192.168.0.0/16 -j DROP
> $IPTABLES -A bad_tcp_packets -i $INET_IFACE -s 10.0.0.0/8 -j DROP
> $IPTABLES -A bad_tcp_packets -i $INET_IFACE -s 172.16.0.0/12 -j DROP
> 
> #
> # Enable simple IP Forwarding and Network Address Translation
> #
> 
> $IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j SNAT --to-source $INET_IP
> 
> #
> # Bad TCP packets we don't want
> #
> 
> $IPTABLES -A FORWARD -p tcp -j bad_tcp_packets
> 
> #
> # Accept the packets we actually want to forward
> #
> 
> $IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
> $IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
> $IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG \
> --log-level DEBUG --log-prefix "IPT FORWARD packet died: "
> 
> #
> # Create separate chains for ICMP, TCP and UDP to traverse
> #
> 
> $IPTABLES -N icmp_packets
> $IPTABLES -N tcp_packets
> $IPTABLES -N udpincoming_packets
> 
> #
> # The allowed chain for TCP connections
> #
> 
> $IPTABLES -N allowed
> $IPTABLES -A allowed -p TCP --syn -j ACCEPT
> $IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
> $IPTABLES -A allowed -p TCP -j DROP
> 
> #
> # ICMP rules
> #
> 
> # Changed rules totally
> $IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
> $IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT
> 
> #
> # TCP rules
> #
> 
> $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
> $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
> $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
> $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed
> 
> #
> # UDP ports
> #
> 
> # nondocumented commenting out of these rules
> #$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
> #$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT
> $IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT
> $IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT
> 
> ##########################
> # INPUT chain
> #
> # Bad TCP packets we don't want.
> #
> 
> $IPTABLES -A INPUT -p tcp -j bad_tcp_packets
> 
> #
> # Rules for incoming packets from the internet.
> #
> 
> $IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
> $IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
> $IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udpincoming_packets
> 
> #
> # Rules for special networks not part of the Internet
> #
> 
> $IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_BCAST_ADRESS -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LAN_IP -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $INET_IP -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT
> $IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state ESTABLISHED,RELATED \
> -j ACCEPT
> $IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
> --log-level DEBUG --log-prefix "IPT INPUT packet died: "
> 
> ###############################
> # OUTPUT chain
> #
> #
> # Bad TCP packets we don't want.
> #
> 
> $IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets
> 
> #
> # Special OUTPUT rules to decide which IP's to allow.
> #
> 
> $IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
> $IPTABLES -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT
> $IPTABLES -A OUTPUT -p ALL -s $INET_IP -j ACCEPT
> 
> #
> # Log weird packets that don't match the above.
> #
> 
> $IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
> --log-level DEBUG --log-prefix "IPT OUTPUT packet died: "
-- 
Alton R. Pouncey, II

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