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Old 10-16-2004, 04:11 PM   #1
LQ Newbie
Registered: Oct 2004
Distribution: debian
Posts: 2

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iptables - strange behaviour of nat??

I set iptables masquerade on "server".... clients has good gateway, and they can ping machines outside nat, dns works too, but nothing else tcp and udp packets goes to server and... are dropped???

I couldn't public dump of tcpdump because I haven't got 5 posts(there are urls) So if someone would like to help me it's there: cobra<dot>eu<dot>org/tcpdump.txt

Last edited by shacky; 10-16-2004 at 04:13 PM.
Old 10-16-2004, 07:29 PM   #2
Registered: Sep 2003
Location: Rawalpindi, Pakistan
Distribution: Slackware
Posts: 86

Rep: Reputation: 15
have you read the IP masquerading HOWTO? If not then visit . Make sure that you use a simple firewall script such as the first time. Use iptables -nvL to see which policy is in action. I hope that helps!
Old 10-17-2004, 10:44 AM   #3
LQ Newbie
Registered: Oct 2004
Distribution: debian
Posts: 2

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it wasn't my first masquerade.... but first where i had to change TTL target this provider checks if TTL is diffrent then 64(linux), 255(windows)..... masquerade decreases TTL by one, so my masq has been sending 63, 254...

iptables -t mangle -A PREROUTING -i eth1 -j TTL --ttl-set 64

and everything is ok
you have to patch kernel with patch-o-matic from


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