Full NAT

modulename: nf_nat.ko

and/or

iptable_nat.ko

and/or

xt_nat.ko

configname: CONFIG_NF_NAT

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>IP: Netfilter Configuration
└─>Full NAT
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
The Full NAT option allows masquerading, port forwarding and other
forms of full Network Address Port Translation. It is controlled by
the `nat' table in iptables: see the man page for iptables(8).

To compile it as a module, choose M here. If unsure, say N.

source code:
net/ipv4/netfilter/