IPv4 NAT

modulename: nf_nat_ipv4.ko

and/or

iptable_nat.ko

configname: CONFIG_NF_NAT_IPV4

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>IP: Netfilter Configuration
└─>IPv4 NAT
In linux kernel since version 3.1 (release Date: 2011-10-24)  
The IPv4 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/
selects
CONFIG_NF_NAT