Explain the steps performed by the Linux kernel during IP address translation.

What will be an ideal response?

In the Linux NAT device PC2, all the incoming packets from the private network will first
transverse the PREROUTING chain, since PREROUTING has the default policy ACCEPT, the kernel will decide whether these packets are for PC2 itself or for some other hosts. Packets for other hosts will then transverse the FORWARD chain which also has the default policy of ACCEPT, the packets are then forward to the POSTROUTING chain, here their private IP addresses will be translated to the public IP address according to the rule set SNAT, Linux will remember the source ports of these packets so that it know which private hosts are the source hosts of these packets (According to the Professor, Linux will also change the source ports of the packets, but from our observation on the captured packets across the
private/public boundary the source ports are unchanged.) The packets will now be sent to the corresponding hosts in the public network. When packets come back from the public network to the private network, they will first transverse the PREROUTING chain and then the FORWARD chain, finally they arrive at the POSTROUTING chain; here their IP addresses are changed back to their corresponding private addresses. These packets will now be forward to the private network.