1 This is an experimental demonstration target which inverts the source 2 and destination fields in the IP header and retransmits the packet. 3 It is only valid in the 4 .BR INPUT , 5 .B FORWARD 6 and 7 .B PREROUTING 8 chains, and user-defined chains which are only called from those 9 chains. Note that the outgoing packets are 10 .B NOT 11 seen by any packet filtering chains, connection tracking or NAT, to 12 avoid loops and other problems. 13