Hi all,
Julien Vehent wrote:
On Tue, 28 Oct 2008 12:25:13 +0100, Diego Casado Mansilla
<diego.casadomansilla@xxxxxxxxx> wrote:
Hello all!!!
This is my first mail in the list.
Hopefully the question is interesting and you can figure out how to help
me.
I use iptables rules to manage the connections from internet to my local
network. I know how to filter, do nat, etc...
But this days I'm trying to do NAT in connections that are already
established. The problem is (as far as I know) the packets which pass
throught the nat table are only the SYN packets (once), thus, the
packets that are used to perform a NEW connection.
After that the connection is created, the maintenance and the resolution
of the SNAT and DNAT are kept till the connection finish.
What I'm wondering is: how can I change the ports or IPs of an already
established connection if my packets just go throught the nat table at
the connection time?
What you want is to redirect an existing connection to a new destination.
If you use TCP protocol, the only way to do that is to record the current
connection and, in parralel, create a second connection to you new
destination and replay the payload on the packet in the new one.
If you use UDP, this doesn't apply since there's no connection tracking in
the UDP protocol. Netfilter, however, does some connection tracking on UDP
packets, so make some test to see if it's doable.
I had to solve the same problem in a honeypot project to redirect active
connections from low interaction honeypots to high interactions honeypots.
The solution I choosed was to queue the connections in userland using
netfilter_queue, process them and replay those I've selected to the new
destination in parrallel, and then drop the packet from the initial
connection.
It's tricky to do, and there's many issue to solve, but AFAIK this is the
most reliable solution.
I have also thought in that solution (or something like that), but I was
expecting something easier with iptables-conntrack... :o).
So what I will do is to create a new connection between a C'/S' in my
local machine, and when a packet from the real Server go trouhgt my
transparent-proxi, I will enqueue it, record the pay-load, do something
"tricky" with the ack and seq. number (I think that a substraction
should be enought) and use all this stuff to send the data from S' to
the Real Client...
After that the client replies with an ACK to the real server...thus.. I
have to do a replication of that ACK in order to send one copy to the
real Server and annother one to the S' in order to keep the
TCP-connection state and flow control.
So...Do I must to use annother time the QUEUE to do so?? I think so.
**** Maybe doing packets' replication since those ones are redirected to
annother machine?
Note : window-tracking is for the tracking of the window size in the tcp
header, it has nothing to do with this.
**** NAT TCP Extensions??Patch-O-Matic --> window-tracking??
**** I read this in an interntet site:
--- NEW (and RELATED non-icmp)
This is a very important part relevant for understanding the whole
NAT
subsystem. Only if the packet has the state NEW (i.e. it would
establish
a new connection, if we'd accept it), the NAT table is traversed by
calling ip_nat_rule.c:ip_nat_rule_find(), which in turn calls
ip_tables.c:ipt_do_table() for the actual IP table traversal. The
traversal
ends up in either ACCEPTing the packet as it is, or one of the nat
targets
(SNAT, DNAT and if loaded: REDIRECT, MASQUERADE) Please see
chapter FIXME for further description of those targets.
--- ESTABLISHED
This packet belongs to an already established connection. We don't
need
to traverse the NAT table again, as the necessary information
(struct ip_nat_info) was already gained Hello everybody,
Thank you very much in advance and if my questions are not clear don't
doubt to send me a message.
Diego.
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Regards,
Julien
Thanks and regards,
Diego.
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