nixpkgs/modules/services/networking/nat.nix

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# This module enables Network Address Translation (NAT).
{ config, pkgs, ... }:
with pkgs.lib;
let
cfg = config.networking.nat;
in
{
###### interface
options = {
networking.nat.enable = mkOption {
default = false;
description =
''
Whether to enable Network Address Translation (NAT).
'';
};
networking.nat.internalIPs = mkOption {
example = "192.168.1.0/24";
description =
''
The IP address range for which to perform NAT. Packets
coming from these addresses and destined for the external
interface will be rewritten.
'';
};
networking.nat.externalInterface = mkOption {
example = "eth1";
description =
''
The name of the external network interface.
'';
};
networking.nat.externalIP = mkOption {
default = "";
example = "203.0.113.123";
description =
''
The public IP address to which packets from the local
network are to be rewritten. If this is left empty, the
IP address associated with the external interface will be
used.
'';
};
};
###### implementation
config = mkIf config.networking.nat.enable {
environment.systemPackages = [ pkgs.iptables ];
boot.kernelModules = [ "nf_nat_ftp" ];
jobs.nat =
{ description = "Network Address Translation";
startOn = "started network-interfaces";
path = [ pkgs.iptables ];
preStart =
''
iptables -t nat -F POSTROUTING
iptables -t nat -X
iptables -t nat -A POSTROUTING \
-s ${cfg.internalIPs} -o ${cfg.externalInterface} \
${if cfg.externalIP == ""
then "-j MASQUERADE"
else "-j SNAT --to-source ${cfg.externalIP}"}
echo 1 > /proc/sys/net/ipv4/ip_forward
'';
postStop =
''
iptables -t nat -F POSTROUTING
'';
};
};
}