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- Join Date
- Oct 2008
NAT in already established TCP connections
This is my first post in the linux forum.
I hope you can 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?
- Maybe doing packets' replication since those ones are redirected to annother machine?
- I read this in http://svn.gnumonks.org/trunk/netfil...ls/doc/nat.txt
- 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.
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 as the first packet of this
connection entered the NEW case above. We just use what's in
the struct ip_conntrack.nat.info.
thank you very much in advance.