From 5306b361814c65c9cd16c56f04da5a9e78d7855d Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Wed, 28 Jun 2023 23:51:37 +0100
Subject: [PATCH] ipv4 nat rules

---
 examples/rotuer-firewall.nix | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/examples/rotuer-firewall.nix b/examples/rotuer-firewall.nix
index 249d392..f2a4308 100644
--- a/examples/rotuer-firewall.nix
+++ b/examples/rotuer-firewall.nix
@@ -143,4 +143,28 @@ in {
       # "oifname \"int\" ip6 daddr 2001:8b0:de3a:40de::e9d tcp dport 22"
     ];
   };
+
+  nat-tx = {
+    type = "nat";
+    hook = "postrouting";
+    priority = "100";
+    policy = "accept";
+    family = "ip";
+    rules = [
+      "oifname \"ppp0\" masquerade"
+    ];
+  };
+  nat-rx = {
+    type = "nat";
+    hook = "prerouting";
+    priority = "-100";
+    family = "ip";
+    policy = "accept";
+    rules = [
+      # per https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/security_guide/sec-configuring_nat_using_nftables:
+      # "Even if you do not add a rule to the prerouting chain, the
+      # nftables framework requires this chain to match incoming
+      # packet replies. "
+    ];
+  };
 }