CONFIG_NF_NAT (not configurable)

modulename: nf_nat.ko

and/or

xt_nat.ko

configname: CONFIG_NF_NAT

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>Core Netfilter Configuration
└─>NF_NAT
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
source code:
net/netfilter/