iptables: log connection after SNAT/MASQUERADE command


 
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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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iptables-apply(8)					      System Manager's Manual						 iptables-apply(8)

NAME
iptables-apply - a safer way to update iptables remotely SYNOPSIS
iptables-apply [-hV] [-t timeout] ruleset-file DESCRIPTION
iptables-apply will try to apply a new ruleset (as output by iptables-save/read by iptables-restore) to iptables, then prompt the user whether the changes are okay. If the new ruleset cut the existing connection, the user will not be able to answer affirmatively. In this case, the script rolls back to the previous ruleset after the timeout expired. The timeout can be set with -t. When called as ip6tables-apply, the script will use ip6tables-save/-restore instead. OPTIONS
-t seconds, --timeout seconds Sets the timeout after which the script will roll back to the previous ruleset. -h, --help Display usage information. -V, --version Display version information. SEE ALSO
iptables-restore(8), iptables-save(8), iptables(8). LEGALESE
iptables-apply is copyright by Martin F. Krafft. This manual page was written by Martin F. Krafft <madduck@madduck.net> Permission is granted to copy, distribute and/or modify this document under the terms of the Artistic License 2.0. 2006-06-04 iptables-apply(8)