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Full Discussion: iptables: log connection after SNAT/MASQUERADE command
Special Forums IP Networking iptables: log connection after SNAT/MASQUERADE command Post 302673951 by unlimited on Thursday 19th of July 2012 05:20:55 AM
Old 07-19-2012
iptables: log connection after SNAT/MASQUERADE command
Hello!

I have the following problem with iptables in Debian 6:

My server works as a router and it needs to log server external IP+port for all outgoing connections.

But after command SNAT or MASQUERADE traffic is "lost".
I mean no following rules can catch those traffic.
Everything looks like SNAT/MASQUERADE is the "end" rule and it pushes traffic to network immediately.

Question:

How can I log routed connection data with server external IP and port?

---------- Post updated 19-07-12 at 12:20 PM ---------- Previous update was 18-07-12 at 10:27 PM ----------

These are rules from nat table:

-A POSTROUTING -p tcp -s 10.0.0.0/8 --syn -j MARK --set-mark 4
-A POSTROUTING -m mark --mark 4 -j LOG --log-prefix "TCPLO1 " --log-level debug
-A POSTROUTING -s 10.0.0.0/8 -o eth0 -j SNAT --to-source 12.23.34.56
-A POSTROUTING -m mark --mark 4 -j LOG --log-prefix "TCPLO2 " --log-level debug
-A POSTROUTING -p tcp --syn -j LOG --log-prefix "TCPLO3 " --log-level debug

First rule marks routed connection
second - logs marked connection but it don't contain IP and port selected by NAT.
third - executes SNAT
and next line don't log anything but should log marked connection
last line should log any connections and it logs server's own traffic and not routed connections
 

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LEARN ABOUT DEBIAN

netstat-nat

netstat-nat(1)						      General Commands Manual						    netstat-nat(1)

NAME

       netstat-nat - Show the natted connections on a linux iptable firewall

SYNOPSIS

       netstat-nat [options]

DESCRIPTION

       netstat-nat Displays NAT connections managed by netfilter/iptables which comes with the > 2.4.x linux kernels.

       The  program  reads  its information from '/proc/net/ip_conntrack' or '/proc/net/nf_conntrack', which is the temporary conntrack-storage of
       netfilter.

OPTIONS

       -h     displays help

       -n     don't resolve IPs/portnumbers to host/portnames

       -p <protocol>
	      display NAT connections with protocol selection (see /etc/protocols)

       -s <source host>
	      display connections by source IP/hostname

       -d <destination host>
	      display connections by destination IP/hostname

       -S     display SNAT connections

       -D     display DNAT connections

       -L     display only connections to NAT box self (doesn't show SNAT & DNAT)

       -R     display only connections routed through the NAT box (doesn't show SNAT & DNAT)

       -x     extended view of hostnames

       -r <src|dst|src-port|dst-port|state>
	      sort connections

       -o     no output header

       -N     display NAT box connection information (only valid with SNAT & DNAT)

       -v     prints version

FILES

       /proc/net/ip_conntrack or /proc/net/nf_conntrack

SEE ALSO

       http://www.tweegy.nl/projects/netstat-nat/
       http://www.netfilter.org/

AUTHOR

       netstat-nat has been written by D.Wijsman danny@tweegy.nl
       The manual page has been written by marceln@xs4all.nl

								     July 2002							    netstat-nat(1)
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