Good morning,
I'm a newbie of iptables and as far as I've seen on tutorials on the Internet it seems that both prerouting and postrouting NAT chains are undergone both by a packet that goes from an internal LAN to the Internet and of a one that goes in the opposite direction (from the Internet to the LAN).
AS NAT prerouting is DNAT, i.e. changing of the destination IP address and NAT postrouting is SNAT, i.e. changing of the source IP address, I naturally think that for a packet that exits the internal LAN and goes to the Internet only NAT postrouting is necessary while for a packet that from the Internet goes into the internal LAN only NAT prerouting is necessary.
Can You please take me an example that demonstrates in each of the two cases that also the other NAT chain could be useful (NAT prerouting for a packet that goes from the LAN to the Internet, NAT postrouting for a packet that goes in the opposite direction)?
Please help me!!!
Thank You
Regards
Giacomo Odoardi