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 OPENSOLARIS
ip6tables-save
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)