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365 lines
12 KiB
Nix
365 lines
12 KiB
Nix
# This module enables Network Address Translation (NAT).
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# XXX: todo: support multiple upstream links
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# see http://yesican.chsoft.biz/lartc/MultihomedLinuxNetworking.html
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{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.networking.nat;
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mkDest = externalIP: if externalIP == null
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then "-j MASQUERADE"
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else "-j SNAT --to-source ${externalIP}";
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dest = mkDest cfg.externalIP;
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destIPv6 = mkDest cfg.externalIPv6;
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# Whether given IP (plus optional port) is an IPv6.
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isIPv6 = ip: builtins.length (lib.splitString ":" ip) > 2;
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helpers = import ./helpers.nix { inherit config lib; };
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flushNat = ''
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${helpers}
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ip46tables -w -t nat -D PREROUTING -j nixos-nat-pre 2>/dev/null|| true
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ip46tables -w -t nat -F nixos-nat-pre 2>/dev/null || true
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ip46tables -w -t nat -X nixos-nat-pre 2>/dev/null || true
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ip46tables -w -t nat -D POSTROUTING -j nixos-nat-post 2>/dev/null || true
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ip46tables -w -t nat -F nixos-nat-post 2>/dev/null || true
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ip46tables -w -t nat -X nixos-nat-post 2>/dev/null || true
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ip46tables -w -t nat -D OUTPUT -j nixos-nat-out 2>/dev/null || true
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ip46tables -w -t nat -F nixos-nat-out 2>/dev/null || true
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ip46tables -w -t nat -X nixos-nat-out 2>/dev/null || true
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${cfg.extraStopCommands}
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'';
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mkSetupNat = { iptables, dest, internalIPs, forwardPorts }: ''
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# We can't match on incoming interface in POSTROUTING, so
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# mark packets coming from the internal interfaces.
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${concatMapStrings (iface: ''
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${iptables} -w -t nat -A nixos-nat-pre \
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-i '${iface}' -j MARK --set-mark 1
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'') cfg.internalInterfaces}
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# NAT the marked packets.
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${optionalString (cfg.internalInterfaces != []) ''
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${iptables} -w -t nat -A nixos-nat-post -m mark --mark 1 \
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${optionalString (cfg.externalInterface != null) "-o ${cfg.externalInterface}"} ${dest}
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''}
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# NAT packets coming from the internal IPs.
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${concatMapStrings (range: ''
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${iptables} -w -t nat -A nixos-nat-post \
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-s '${range}' ${optionalString (cfg.externalInterface != null) "-o ${cfg.externalInterface}"} ${dest}
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'') internalIPs}
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# NAT from external ports to internal ports.
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${concatMapStrings (fwd: ''
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${iptables} -w -t nat -A nixos-nat-pre \
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-i ${toString cfg.externalInterface} -p ${fwd.proto} \
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--dport ${builtins.toString fwd.sourcePort} \
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-j DNAT --to-destination ${fwd.destination}
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${concatMapStrings (loopbackip:
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let
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matchIP = if isIPv6 fwd.destination then "[[]([0-9a-fA-F:]+)[]]" else "([0-9.]+)";
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m = builtins.match "${matchIP}:([0-9-]+)" fwd.destination;
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destinationIP = if m == null then throw "bad ip:ports `${fwd.destination}'" else elemAt m 0;
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destinationPorts = if m == null then throw "bad ip:ports `${fwd.destination}'" else builtins.replaceStrings ["-"] [":"] (elemAt m 1);
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in ''
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# Allow connections to ${loopbackip}:${toString fwd.sourcePort} from the host itself
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${iptables} -w -t nat -A nixos-nat-out \
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-d ${loopbackip} -p ${fwd.proto} \
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--dport ${builtins.toString fwd.sourcePort} \
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-j DNAT --to-destination ${fwd.destination}
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# Allow connections to ${loopbackip}:${toString fwd.sourcePort} from other hosts behind NAT
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${iptables} -w -t nat -A nixos-nat-pre \
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-d ${loopbackip} -p ${fwd.proto} \
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--dport ${builtins.toString fwd.sourcePort} \
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-j DNAT --to-destination ${fwd.destination}
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${iptables} -w -t nat -A nixos-nat-post \
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-d ${destinationIP} -p ${fwd.proto} \
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--dport ${destinationPorts} \
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-j SNAT --to-source ${loopbackip}
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'') fwd.loopbackIPs}
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'') forwardPorts}
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'';
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setupNat = ''
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${helpers}
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# Create subchains where we store rules
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ip46tables -w -t nat -N nixos-nat-pre
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ip46tables -w -t nat -N nixos-nat-post
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ip46tables -w -t nat -N nixos-nat-out
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${mkSetupNat {
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iptables = "iptables";
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inherit dest;
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inherit (cfg) internalIPs;
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forwardPorts = filter (x: !(isIPv6 x.destination)) cfg.forwardPorts;
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}}
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${optionalString cfg.enableIPv6 (mkSetupNat {
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iptables = "ip6tables";
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dest = destIPv6;
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internalIPs = cfg.internalIPv6s;
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forwardPorts = filter (x: isIPv6 x.destination) cfg.forwardPorts;
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})}
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${optionalString (cfg.dmzHost != null) ''
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iptables -w -t nat -A nixos-nat-pre \
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-i ${toString cfg.externalInterface} -j DNAT \
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--to-destination ${cfg.dmzHost}
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''}
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${cfg.extraCommands}
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# Append our chains to the nat tables
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ip46tables -w -t nat -A PREROUTING -j nixos-nat-pre
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ip46tables -w -t nat -A POSTROUTING -j nixos-nat-post
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ip46tables -w -t nat -A OUTPUT -j nixos-nat-out
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'';
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in
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{
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###### interface
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options = {
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networking.nat.enable = mkOption {
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type = types.bool;
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default = false;
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description =
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''
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Whether to enable Network Address Translation (NAT).
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'';
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};
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networking.nat.enableIPv6 = mkOption {
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type = types.bool;
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default = false;
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description =
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''
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Whether to enable IPv6 NAT.
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'';
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};
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networking.nat.internalInterfaces = mkOption {
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type = types.listOf types.str;
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default = [];
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example = [ "eth0" ];
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description =
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''
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The interfaces for which to perform NAT. Packets coming from
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these interface and destined for the external interface will
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be rewritten.
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'';
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};
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networking.nat.internalIPs = mkOption {
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type = types.listOf types.str;
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default = [];
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example = [ "192.168.1.0/24" ];
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description =
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''
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The IP address ranges for which to perform NAT. Packets
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coming from these addresses (on any interface) and destined
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for the external interface will be rewritten.
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'';
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};
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networking.nat.internalIPv6s = mkOption {
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type = types.listOf types.str;
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default = [];
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example = [ "fc00::/64" ];
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description =
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''
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The IPv6 address ranges for which to perform NAT. Packets
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coming from these addresses (on any interface) and destined
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for the external interface will be rewritten.
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'';
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};
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networking.nat.externalInterface = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = "eth1";
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description =
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''
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The name of the external network interface.
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'';
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};
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networking.nat.externalIP = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = "203.0.113.123";
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description =
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''
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The public IP address to which packets from the local
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network are to be rewritten. If this is left empty, the
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IP address associated with the external interface will be
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used.
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'';
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};
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networking.nat.externalIPv6 = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = "2001:dc0:2001:11::175";
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description =
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''
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The public IPv6 address to which packets from the local
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network are to be rewritten. If this is left empty, the
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IP address associated with the external interface will be
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used.
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'';
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};
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networking.nat.forwardPorts = mkOption {
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type = with types; listOf (submodule {
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options = {
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sourcePort = mkOption {
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type = types.either types.int (types.strMatching "[[:digit:]]+:[[:digit:]]+");
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example = 8080;
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description = "Source port of the external interface; to specify a port range, use a string with a colon (e.g. \"60000:61000\")";
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};
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destination = mkOption {
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type = types.str;
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example = "10.0.0.1:80";
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description = "Forward connection to destination ip:port (or [ipv6]:port); to specify a port range, use ip:start-end";
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};
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proto = mkOption {
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type = types.str;
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default = "tcp";
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example = "udp";
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description = "Protocol of forwarded connection";
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};
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loopbackIPs = mkOption {
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type = types.listOf types.str;
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default = [];
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example = literalExample ''[ "55.1.2.3" ]'';
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description = "Public IPs for NAT reflection; for connections to `loopbackip:sourcePort' from the host itself and from other hosts behind NAT";
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};
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};
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});
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default = [];
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example = [
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{ sourcePort = 8080; destination = "10.0.0.1:80"; proto = "tcp"; }
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{ sourcePort = 8080; destination = "[fc00::2]:80"; proto = "tcp"; }
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];
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description =
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''
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List of forwarded ports from the external interface to
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internal destinations by using DNAT. Destination can be
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IPv6 if IPv6 NAT is enabled.
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'';
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};
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networking.nat.dmzHost = mkOption {
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type = types.nullOr types.str;
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default = null;
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example = "10.0.0.1";
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description =
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''
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The local IP address to which all traffic that does not match any
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forwarding rule is forwarded.
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'';
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};
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networking.nat.extraCommands = mkOption {
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type = types.lines;
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default = "";
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example = "iptables -A INPUT -p icmp -j ACCEPT";
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description =
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''
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Additional shell commands executed as part of the nat
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initialisation script.
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'';
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};
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networking.nat.extraStopCommands = mkOption {
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type = types.lines;
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default = "";
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example = "iptables -D INPUT -p icmp -j ACCEPT || true";
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description =
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''
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Additional shell commands executed as part of the nat
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teardown script.
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'';
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};
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};
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###### implementation
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config = mkMerge [
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{ networking.firewall.extraCommands = mkBefore flushNat; }
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(mkIf config.networking.nat.enable {
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assertions = [
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{ assertion = cfg.enableIPv6 -> config.networking.enableIPv6;
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message = "networking.nat.enableIPv6 requires networking.enableIPv6";
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}
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{ assertion = (cfg.dmzHost != null) -> (cfg.externalInterface != null);
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message = "networking.nat.dmzHost requires networking.nat.externalInterface";
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}
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{ assertion = (cfg.forwardPorts != []) -> (cfg.externalInterface != null);
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message = "networking.nat.forwardPorts requires networking.nat.externalInterface";
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}
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];
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environment.systemPackages = [ pkgs.iptables ];
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boot = {
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kernelModules = [ "nf_nat_ftp" ];
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kernel.sysctl = {
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"net.ipv4.conf.all.forwarding" = mkOverride 99 true;
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"net.ipv4.conf.default.forwarding" = mkOverride 99 true;
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} // optionalAttrs cfg.enableIPv6 {
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# Do not prevent IPv6 autoconfiguration.
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# See <http://strugglers.net/~andy/blog/2011/09/04/linux-ipv6-router-advertisements-and-forwarding/>.
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"net.ipv6.conf.all.accept_ra" = mkOverride 99 2;
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"net.ipv6.conf.default.accept_ra" = mkOverride 99 2;
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# Forward IPv6 packets.
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"net.ipv6.conf.all.forwarding" = mkOverride 99 true;
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"net.ipv6.conf.default.forwarding" = mkOverride 99 true;
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};
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};
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networking.firewall = mkIf config.networking.firewall.enable {
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extraCommands = setupNat;
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extraStopCommands = flushNat;
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};
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systemd.services = mkIf (!config.networking.firewall.enable) { nat = {
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description = "Network Address Translation";
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wantedBy = [ "network.target" ];
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after = [ "network-pre.target" "systemd-modules-load.service" ];
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path = [ pkgs.iptables ];
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unitConfig.ConditionCapability = "CAP_NET_ADMIN";
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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};
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script = flushNat + setupNat;
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postStop = flushNat;
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}; };
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})
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];
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}
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