I've tried to enable a NAT rule to translate from 4 private /24 network to 1 public /24 network, but fwbuilder answer with the following message ""Original and translated source should both be networks of the same size."
Is there any way to make this kind of NAT with fwbuilder ?
assuming you use fwbuilder to configure iptables firewall, the problem here is not with fwbuilder but with iptables. There is no straightforward way to build a rule to translate 4 /24 networks into 1 /24 network with iptables. You could try to create an Address Range object to represent the outside /24 network and use it in "Translated Source". This should build a rule with "-j SNAT -to-source A.A.A.1-A.A.A.255" . You can use your four internal networks in "Original Source" column of this NAT rule, this should be fine.