If you’re trying to make an entire network appear as one address when devices on that network connect to that Internet you need to use source NAT. After all you’re trying to translate the SOURCE address of the packet to a public IP address. Source NAT is of course configured in the srcnat chain.
The srcnat chain only has ‘src-nat’ and ‘masquerade’ as available options. They are both mostly the same thing, with one crucial difference: ‘src-nat’ also requires you to specify a ‘to-address’, which is the address that the source IP address of a packet will be changed to in its header. ‘masquerade’ automagically picks the preferred source address of the interface and you don’t have to specify a ‘to-address’. If you have a static public IP it’s best practice to use ‘src-nat’ and manually set the ‘to-address’ to your static IP. If you have a dynamic public IP (you are running a DHCP client on your WAN interface) you have to pick ‘masquerade’.
