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Old 05-16-2001, 12:55 PM   #1
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Registered: May 2001
Posts: 4

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I have installed Red Hat 7.1 on a machine and begun attempting to create a firewall using iptables. I believe I know what I need to do to make it happen but I began to write a script file which does not work as I expect it to. I shortened the file up to try to figure out what's happening. This is my script named rc.firewall

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
exit 0

iptables is the program name, -P means change the default policy of the chain, INPUT is the chain, and DROP is the policy I want.

If I type the lines for iptables from the prompt the policy changes as expected.

When I attempt to run my script by typing sh rc.firewall, from the appropriate directory, I get the following,

iptables: Bad policy name
iptables: Bad policy name
iptables: Bad policy name
'c.firewall: exit: bad non-numeric arg `0

It appears to me that iptables is run from the script, it recognizes the -P to change the policy, I believe it recognizes the chain name but drops the ball on the policy. Yes it is case sensitive and I am using the correct case. I have tried both. Further it does not seem to recognize 0 (zero) as a valid arguement after exit. However, typing sh to enter the shell then exit 0 doesn't generate an error message. Just for more info from the shell I typed exit n , a letter instead of a number and got the error message. Also I edited the script and put a semi-colon after the zero and that error message went away. Okay, what have I done wrong? Thanks in advance to whoever knows whats going on.
Old 05-17-2001, 07:11 PM   #2
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Registered: May 2001
Location: Bristol, UK
Distribution: Slackware, Fedora, RHES
Posts: 2,243

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Question No definate answer, just an idea...

Try using a different shell. Try say tcsh or specifiying bash directly (I assume that RH using bash to replace sh anyway [sorry - I'm a Slackware man]).

See if that changes anything. I use the follwing fine:

#setup the masquerading rules using ipchains
echo "Activating IPv4 packet forwarding..."
echo 1 > /proc/sys/net/ipv4/ip_forward
/sbin/ipchains -P forward DENY
/sbin/ipchains -A forward -s -j MASQ

ipchains -A input -i eth1 --destination-port 123 -p tcp -j ACCEPT
ipchains -A input -i eth1 --destination-port 123 -p udp -j ACCEPT

#allow connections to my http server...
ipchains -A input -i eth1 --destination-port 80 -p tcp -j ACCEPT
ipchains -A input -i eth1 --destination-port 80 -p udp -j ACCEPT

#lets filter out some ports! DENY causes the packet to be dropped so
#the person trying to connect gets a long delay not just a rejected
#connection reply. Make port scanners have to wait a long time!
#filter anything coming into a port <=1024
/sbin/ipchains -A input -i eth1 -s --destination-port 0:1024 -p tcp -



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