IpTables Structure

#
# (PACKET IN)->-[PREROUTING]->- ->----------->-[FORWARD]->------------>- ->-[POSTROUTING]->-(PACKET OUT)
#               -mangle        |               -mangle                  |   -mangle
#               -nat (dst)     |               -filter                  |   -nat (src)
#                              |                                        |
#                               ->-[INPUT]->-(APPLICATION)->-[OUTPUT]->-
#                                  -mangle                   -mangle
#                                  -filter                   -filter
#                                                            -nat (dst)
#