RE: Problem with connection-tracking and FTP

["Mark E. Donaldson" <markee@bandwidthco.com>]

[-- Attachment #1: Type: text/plain, Size: 6057 bytes --]

It would appear you are assuming the FTP server will choose port 1024 for
passive mode ftp.  This is not correct, as it may choose any unprivileged
port up to 65535.  That is one problem you are having.  Also, check your
syntax for "passive mode".  You have made an error with some not needed
colons (:).
Here is a good rule set that will permit all ftp operations - active and
passive:
 
######################
# FTP SERVICES
######################
UNPRIVPORTS="1024:65535"
 
# CONTROL PORT (Active & Passive Mode)
$IPT -t filter -A TCP_RULES -i $FW_INET_IFACE -p tcp --source-port
$UNPRIVPORTS --destination-port 21 -m state --state NEW -j LOG --log-level
$LOG_LEVEL --log-prefix "FTP ACCESS -> "

$IPT -t filter -A TCP_RULES -i $FW_INET_IFACE -p tcp --source-port
$UNPRIVPORTS --destination-port 21 -m state --state NEW -j ACCEPT
 
# DATA PORT (Active Mode)
$IPT -t filter -A TCP_RULES -o $FW_INET_IFACE -p tcp --source-port 20
--destination-port $UNPRIVPORTS -m state --state NEW -j LOG --log-level
$LOG_LEVEL --log-prefix "FTP A-DATA -> "

$IPT -t filter -A TCP_RULES -o $FW_INET_IFACE -p tcp --source-port 20
--destination-port $UNPRIVPORTS -m state --state NEW -j ACCEPT
 
# DATA PORT (Passive Mode)
$IPT -t filter -A TCP_RULES -i $FW_INET_IFACE -p tcp --source-port
$UNPRIVPORTS --destination-port $UNPRIVPORTS -m state --state NEW -j LOG
--log-level $LOG_LEVEL --log-prefix "FTP P-DATA -> "

$IPT -t filter -A TCP_RULES -i $FW_INET_IFACE -p tcp --source-port
$UNPRIVPORTS --destination-port $UNPRIVPORTS -m state --state NEW -j ACCEPT


  _____  

From: netfilter-admin@lists.netfilter.org
[mailto:netfilter-admin@lists.netfilter.org] On Behalf Of Christian Gmeiner
Sent: Tuesday, January 20, 2004 8:01 AM
To: netfilter@lists.netfilter.org
Subject: Problem with connection-tracking and FTP


Hi everybody.
 
I am working on a little firewall script. Everything works just fine, but i
dont get the ftp protocoll working.
 
I call this two function to get ftp working:
 
# ==================================
FTP()
{
    ebegin "Seting rules for active/passive FTP"
 
    # Port 21
 
    iptables -A INPUT     -p tcp --sport 21 -m state --state ESTABLISHED -j
ACCEPT 
    iptables -A OUTPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j
ACCEPT 
 
    # aktiv
    iptables -A INPUT     -p tcp --sport 20 -m state --state
ESTABLISHED,RELATED -j ACCEPT 
    iptables -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j
ACCEPT 
 
    # passiv
    iptables -A INPUT     -p tcp --sport 1024: --dport 1024:  -m state
--state ESTABLISHED -j ACCEPT 
    iptables -A OUTPUT -p tcp --sport 1024: --dport 1024:  -m state --state
ESTABLISHED,RELATED -j ACCEPT 
 
    eend $?
}
 

# ==================================
loadmodules()
{
    ebegin "Try to load needed modules"
 
    /sbin/modprobe ip_tables
    /sbin/modprobe iptable_filter
    /sbin/modprobe ip_conntrack
    /sbin/modprobe ip_conntrack_ftp
    /sbin/modprobe ipt_ULOG
    eend $?
}
 
An here my start function
# ==================================
start() 
{
    ebegin "Starting Firewall"
 
    loadmodules
 
    einfo "Setting default rules to drop"
    iptables -F
    iptables -X 
    iptables -Z 
    iptables -F INPUT
    iptables -F OUTPUT
    iptables -F FORWARD
 
    iptables -P FORWARD DROP
    iptables -P INPUT   DROP
    iptables -P OUTPUT  DROP
 
    acceptlocal
    portscan
    proc
    iana
    illigalpackages
    spoofing
    FTP
 
    # set rules
    InOutTCP
    InTCP
    OutTCP
    InOutUDP
    InUDP
    OutUDP
 
    # Erlaube dem Client routen durch NAT (Network Address Translation
    iptables -t nat -A POSTROUTING -o ${EXT_INT} -j MASQUERADE
    echo "1" > /proc/sys/net/ipv4/ip_forward
 
    eend $? "Failed to start Firewall"
}
 
 
And here are the ports i allow with the function InOut*, In*, Out*,...
 
# TCP in+out
#
TCP_IN_OUT="ssh 10000 smtp pop3 http https"
 
# TCP out
#
# 5190 = ICQ
#
TCP_OUT="5190 http https irc 25 ftp ftp-data"
 
# TCP in
#
TCP_IN=""
 
# UDP in+out
#
UDP_IN_OUT="domain ssh 10000 pop3 ssh"
 
# UDP out
#
UDP_OUT="https irc"
 
# UDP in
#
UDP_IN=""
 
 
Oh and here some important functions:
 
# ==================================
InOutTCP()
{
    ebegin "Allowing in and outbound TCP-traffic"
 
    for i in ${TCP_IN_OUT}
    do
        einfo "   <-> Seting TCP "in" and "out" rules for ${i}"
 
        iptables -A INPUT  -j ACCEPT -i ${EXT_INT} -p tcp --dport ${i} -m
state --state NEW,ESTABLISHED,RELATED
        iptables -A OUTPUT -j ACCEPT -o ${EXT_INT} -p tcp --sport ${i}
--dport 1024: -m state --state ESTABLISHED,RELATED
        iptables -A FORWARD  -j ACCEPT -i ${EXT_INT} -p tcp --dport ${i} -m
state --state NEW,ESTABLISHED,RELATED
        iptables -A FORWARD -j ACCEPT -o ${EXT_INT} -p tcp --sport ${i} -m
state --state ESTABLISHED,RELATED
 
        iptables -A OUTPUT -j ACCEPT -o ${EXT_INT} -p tcp --sport 1024:
--dport ${i} -m state --state NEW,ESTABLISHED,RELATED
        iptables -A INPUT  -j ACCEPT -i ${EXT_INT} -p tcp --sport ${i} -m
state --state ESTABLISHED,RELATED
        iptables -A FORWARD -j ACCEPT -o ${EXT_INT} -p tcp -s ${LAN} --sport
1024: --dport ${i} -m state --state NEW,ESTABLISHED,RELATED
        iptables -A FORWARD  -j ACCEPT -i ${EXT_INT} -p tcp --sport ${i} -d
${LAN} -m state --state ESTABLISHED,RELATED
    done
 
    eend $?
}
 
# ================================== 
OutTCP()
{
    ebegin "Allowing outbound TCP-traffic"
 
    for i in ${TCP_OUT}
    do
        einfo "   <-> Seting TCP "out" rules for ${i}"
 
        iptables -A OUTPUT -j ACCEPT -o ${EXT_INT} -p tcp --sport 1024:
--dport $i -m state --state NEW,ESTABLISHED,RELATED
        iptables -A INPUT  -j ACCEPT -i ${EXT_INT} -p tcp --sport $i -m
state --state ESTABLISHED,RELATED
        iptables -A FORWARD -j ACCEPT -o ${EXT_INT} -p tcp -s ${LAN} --sport
1024: --dport $i -m state --state NEW,ESTABLISHED,RELATED
        iptables -A FORWARD  -j ACCEPT -i ${EXT_INT} -p tcp --sport $i -d
${LAN} -m state --state ESTABLISHED,RELATED
    done
 
    eend $?
}
 
I hope somebody can help me.
 
Thanks, Christian Gmeiner
 
 

[-- Attachment #2: Type: text/html, Size: 11300 bytes --]