iptable forward packet

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Operating Systems Linux Ubuntu iptable forward packet
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iptable forward packet

I have the doubt which involved following configuration.
Comp1 sends icmp packet to main. Main takes that packet and changes destination address to comp2 and source address to it own.
I can capture the packet send from comp1 to main using netfilter. I can see the packet and its content. Then i modify the destination, source address and ip checksum successfully. But when i release it back to the kernel the packet never goes back to comp2. To release back packet i use nfq_set_verdict(....,NF_ACCEPT). If i capture packet from output chain of main when its sending ping reply back to comp1 my program modifies that packet and sends it to comp2 but if i capture packet from input chain of filter table than it does not forward that to modified address. I think this maybe because once the packet is in input chain of filter table modifying destination address means nothing. Can someone assist me how to forward packet from comp1 to comp2 through main.
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ldns(3) 						     Library Functions Manual							   ldns(3)

ldns_pkt_edns, ldns_pkt_edns_udp_size, ldns_pkt_edns_extended_rcode, ldns_pkt_edns_version, ldns_pkt_edns_z, ldns_pkt_edns_data, ldns_pkt_set_edns_udp_size, ldns_pkt_set_edns_extended_rcode, ldns_pkt_set_edns_version, ldns_pkt_set_edns_z, ldns_pkt_set_edns_data- SYNOPSIS
#include <stdint.h> #include <stdbool.h> #include <ldns/ldns.h> bool ldns_pkt_edns(const ldns_pkt *packet); uint16_t ldns_pkt_edns_udp_size(const ldns_pkt *packet); uint8_t ldns_pkt_edns_extended_rcode(const ldns_pkt *packet); uint8_t ldns_pkt_edns_version(const ldns_pkt *packet); uint16_t ldns_pkt_edns_z(const ldns_pkt *packet); ldns_rdf* ldns_pkt_edns_data(const ldns_pkt *packet); void ldns_pkt_set_edns_udp_size(ldns_pkt *packet, uint16_t s); void ldns_pkt_set_edns_extended_rcode(ldns_pkt *packet, uint8_t c); void ldns_pkt_set_edns_version(ldns_pkt *packet, uint8_t v); void ldns_pkt_set_edns_z(ldns_pkt *packet, uint16_t z); void ldns_pkt_set_edns_data(ldns_pkt *packet, ldns_rdf *data); DESCRIPTION
ldns_pkt_edns() returns true if this packet needs and EDNS rr to be sent. At the moment the only reason is an expected packet size larger than 512 bytes, but for instance dnssec would be a good reason too. packet: the packet to check Returns true if packet needs edns rr ldns_pkt_edns_udp_size() return the packet's edns udp size packet: the packet Returns the size ldns_pkt_edns_extended_rcode() return the packet's edns extended rcode packet: the packet Returns the rcode ldns_pkt_edns_version() return the packet's edns version packet: the packet Returns the version ldns_pkt_edns_z() return the packet's edns z value packet: the packet Returns the z value ldns_pkt_edns_data() return the packet's edns data packet: the packet Returns the data ldns_pkt_set_edns_udp_size() Set the packet's edns udp size packet: the packet s: the size ldns_pkt_set_edns_extended_rcode() Set the packet's edns extended rcode packet: the packet c: the code ldns_pkt_set_edns_version() Set the packet's edns version packet: the packet v: the version ldns_pkt_set_edns_z() Set the packet's edns z value packet: the packet z: the value ldns_pkt_set_edns_data() Set the packet's edns data packet: the packet data: the data AUTHOR
The ldns team at NLnet Labs. Which consists out of Jelte Jansen and Miek Gieben. REPORTING BUGS
Please report bugs to ldns-team@nlnetlabs.nl or in our bugzilla at http://www.nlnetlabs.nl/bugs/index.html COPYRIGHT
Copyright (c) 2004 - 2006 NLnet Labs. Licensed under the BSD License. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. SEE ALSO
ldns_pkt. And perldoc Net::DNS, RFC1034, RFC1035, RFC4033, RFC4034 and RFC4035. REMARKS
This manpage was automaticly generated from the ldns source code by use of Doxygen and some perl. 30 May 2006 ldns(3)

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