01-10-2012
How to configure Full Cone NAT using iptables ?
Hi Experts;
I want to find the right iptables commands combination to address the following need:
- NEs are NATed thru the linux box (using iptables) towards the WAN cloud, where the NTP servers are situated.
- In order to achieve redundancy, the NTP Servers are in a load balancing cluster with one virtual IP address (172.30.4.245)
- The problem is that when the NEs request for NTP updates using the 172.30.4.245, the NTP response is received from one of the actual IP addresses (.200, .230 .240).
Example:
The iptables is not allowing this flow, which is a normal behaviour since the requested vs responding address are not the same (172.30.4.245 vs 172.30.4.230) :
Request : UDP 10.68.2.11:23445 ---> 172.30.4.245:123 (this is Before NAT, of course after NAT the source is 10.23.14.72)
Response: UDP 172.30.4.230:123 ---> 10.23.14.72:23445 (Response to the WAN address)
I'm wondering if there is any way to let iptables establish the UDP flow only based on the (s-port/d-port) regardless of the IP addresses, and execute the NAT back to the LAN based on that.
UDP/NTP is just an example, almost all the needed services are setup in the same way (load balancing in Cluster).
Appreciate your help !
Thanks & Regards
lvl1s7a
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LEARN ABOUT POSIX
iptables-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)