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-SAVE(8)                                                  iptables 1.6.1                                                  IPTABLES-SAVE(8)

NAME
iptables-save -- dump iptables rules to stdout ip6tables-save -- dump iptables rules to stdout SYNOPSIS
iptables-save [-M modprobe] [-c] [-t table] ip6tables-save [-M modprobe] [-c] [-t table] DESCRIPTION
iptables-save and ip6tables-save are used to dump the contents of IP or IPv6 Table in easily parseable format to STDOUT. Use I/O-redirect- ion provided by your shell to write to a file. -M, --modprobe modprobe_program Specify the path to the modprobe program. By default, iptables-save will inspect /proc/sys/kernel/modprobe to determine the exe- cutable's path. -c, --counters include the current values of all packet and byte counters in the output -t, --table tablename restrict output to only one table. If not specified, output includes all available tables. BUGS
None known as of iptables-1.2.1 release AUTHORS
Harald Welte <laforge@gnumonks.org> Rusty Russell <rusty@rustcorp.com.au> Andras Kis-Szabo <kisza@sch.bme.hu> contributed ip6tables-save. SEE ALSO
iptables-apply(8),iptables-restore(8), iptables(8) The iptables-HOWTO, which details more iptables usage, the NAT-HOWTO, which details NAT, and the netfilter-hacking-HOWTO which details the internals. iptables 1.6.1 IPTABLES-SAVE(8)