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Old 04-16-2004, 01:50 PM   #1
ldp
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Registered: Apr 2004
Location: Belgium Antwerpen
Distribution: slackware - knoppix
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iptables firewall seems to work but strange output in dmesg.


Hello,
I installed a iptables which I took from the ipmasquerading howto and it seems to work fine but I'm a little worried about the output it gives when activating it.

ip_tables: (C) 2000-2002 Netfilter core team
ip_conntrack version 2.1 (768 buckets, 6144 max) - 292 bytes per conntrack
IN=eth1 OUT= MAC= SRC=81.165.225.138 DST=81.165.231.255 LEN=96 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=137 DPT=137 LEN=76
IN=eth1 OUT= MAC= SRC=81.165.225.138 DST=81.165.231.255 LEN=96 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=137 DPT=137 LEN=76
IN=eth1 OUT= MAC= SRC=81.165.225.138 DST=81.165.231.255 LEN=96 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=137 DPT=137 LEN=76
...

Does this matter and/or what does it mean? just bogus? This only appears when booting the linux rtr/fw machine not when I run the script manually.

thanks for any advice.
 
Old 04-16-2004, 07:04 PM   #2
slacky
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UDP Port 137 is Windows Netbios traffic - is there a Windows machine on your network?
 
Old 04-17-2004, 02:26 AM   #3
muah
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It seems like dropped packets which would be usually logged but syslogd isnt running at that time yet.
 
Old 04-17-2004, 02:00 PM   #4
ldp
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there is idd a windowsxp machine behind the linux rtr/fw. But it was powered off while this text was logged. I think that it's some output from my iptables script but it doesn't show when I run it manually.


FWVER=0.80s
echo -e "\nLoading rc.firewall - version $FWVER..\n"

IPTABLES=/sbin/iptables
LSMOD=/sbin/lsmod
DEPMOD=/sbin/depmod
MODPROBE=/sbin/modprobe
GREP=/bin/grep
AWK=/usr/bin/awk
SED=/bin/sed
IFCONFIG=/sbin/ifconfig

EXTIF="eth1"
INTIF="eth0"
echo " External Interface: $EXTIF"
echo " Internal Interface: $INTIF"
echo " ---"

EXTIP="`$IFCONFIG $EXTIF | $AWK \
/$EXTIF/'{next}//{split($0,a,":");split(a[2],a," ");print a[1];exit}'`"

echo " External IP: $EXTIP"
echo " ---"

INTNET="192.168.0.0/24"
INTIP="192.168.0.1/24"
echo " Internal Network: $INTNET"
echo " Internal IP: $INTIP"
echo " ---"

UNIVERSE="0.0.0.0/0"

echo " - Verifying that all kernel modules are ok"
$DEPMOD -a
echo -en " Loading kernel modules: "

echo -en "ip_tables, "
if [ -z "` $LSMOD | $GREP ip_tables | $AWK {'print $1'} `" ]; then
$MODPROBE ip_tables
fi

echo -en "ip_conntrack, "
if [ -z "` $LSMOD | $GREP ip_conntrack | $AWK {'print $1'} `" ]; then
$MODPROBE ip_conntrack
fi

echo -e "ip_conntrack_ftp, "
if [ -z "` $LSMOD | $GREP ip_conntrack_ftp | $AWK {'print $1'} `" ]; then
$MODPROBE ip_conntrack_ftp
fi

echo -en "iptable_nat, "
if [ -z "` $LSMOD | $GREP iptable_nat | $AWK {'print $1'} `" ]; then
$MODPROBE iptable_nat
fi

echo -e "ip_nat_ftp"
if [ -z "` $LSMOD | $GREP ip_nat_ftp | $AWK {'print $1'} `" ]; then
$MODPROBE ip_nat_ftp
fi

echo " ---"

echo " Enabling forwarding.."
echo "1" > /proc/sys/net/ipv4/ip_forward
echo " Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr

echo " ---"

echo " Clearing any existing rules and setting default policy to DROP.."
$IPTABLES -P INPUT DROP
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT DROP
$IPTABLES -F OUTPUT
$IPTABLES -P FORWARD DROP
$IPTABLES -F FORWARD
$IPTABLES -F -t nat

if [ -n "`$IPTABLES -L | $GREP drop-and-log-it`" ]; then
$IPTABLES -F drop-and-log-it
fi

$IPTABLES -X
$IPTABLES -Z

echo " Creating a DROP chain.."
$IPTABLES -N drop-and-log-it
$IPTABLES -A drop-and-log-it -j LOG --log-level info
$IPTABLES -A drop-and-log-it -j REJECT

echo -e "\n - Loading INPUT rulesets"
$IPTABLES -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT
$IPTABLES -A INPUT -i $INTIF -s $INTNET -d $UNIVERSE -j ACCEPT
$IPTABLES -A INPUT -i $EXTIF -s $INTNET -d $UNIVERSE -j drop-and-log-it
$IPTABLES -A INPUT -i $EXTIF -s $UNIVERSE -d $EXTIP -m state --state \
ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it

echo -e " - Loading OUTPUT rulesets"
$IPTABLES -A OUTPUT -o lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT
$IPTABLES -A OUTPUT -o $INTIF -s $EXTIP -d $INTNET -j ACCEPT
$IPTABLES -A OUTPUT -o $INTIF -s $INTIP -d $INTNET -j ACCEPT
$IPTABLES -A OUTPUT -o $EXTIF -s $UNIVERSE -d $INTNET -j drop-and-log-it
$IPTABLES -A OUTPUT -o $EXTIF -s $EXTIP -d $UNIVERSE -j ACCEPT
$IPTABLES -A OUTPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it

echo -e " - Loading FORWARD rulesets"
echo " - FWD: Allow all connections OUT and only existing/related IN"
$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED \
-j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
$IPTABLES -A FORWARD -j drop-and-log-it

echo " - NAT: Enabling SNAT (MASQUERADE) functionality on $EXTIF"
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j SNAT --to $EXTIP
echo -e "\nStronger rc.firewall $FWVER done. Will it fsck my system?\n"


If this are dropped packets then I guess that it doesn't really matter anyway.
thanks for the replies already.
rgds,
Lieven
 
  


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