diff --git a/src/iptables.rs b/src/iptables.rs
index 1cc82f7..bed2371 100644
--- a/src/iptables.rs
+++ b/src/iptables.rs
@@ -158,16 +158,16 @@ pub(crate) async fn forward_postrouting(
     proto: Proto,
     internal_ip: Ipv4Addr,
     internal_mask: u8,
+    internal_port: u16,
     external_ip: Ipv4Addr,
-    external_port: u16,
     destination_ip: Ipv4Addr,
 ) -> Result<(), anyhow::Error> {
     forward_postrouting_snat(
         proto,
         internal_ip,
         internal_mask,
+        internal_port,
         external_ip,
-        external_port,
         destination_ip,
         |cmd| cmd.arg("-I"),
     )
@@ -178,16 +178,16 @@ pub(crate) async fn delete_forward_postrouting(
     proto: Proto,
     internal_ip: Ipv4Addr,
     internal_mask: u8,
+    internal_port: u16,
     external_ip: Ipv4Addr,
-    external_port: u16,
     destination_ip: Ipv4Addr,
 ) -> Result<(), anyhow::Error> {
     forward_postrouting_snat(
         proto,
         internal_ip,
         internal_mask,
+        internal_port,
         external_ip,
-        external_port,
         destination_ip,
         |cmd| cmd.arg("-D"),
     )
@@ -198,8 +198,8 @@ async fn forward_postrouting_snat(
     proto: Proto,
     internal_ip: Ipv4Addr,
     internal_mask: u8,
+    internal_port: u16,
     external_ip: Ipv4Addr,
-    external_port: u16,
     destination_ip: Ipv4Addr,
     func: impl Fn(&mut Command) -> &mut Command,
 ) -> Result<(), anyhow::Error> {
@@ -215,7 +215,7 @@ async fn forward_postrouting_snat(
             "-m",
             proto.as_iptables_str(),
             "--dport",
-            &external_port.to_string(),
+            &internal_port.to_string(),
             "-m",
             "conntrack",
             "--ctstate",
diff --git a/src/rules.rs b/src/rules.rs
index 0a47cc8..1978c19 100644
--- a/src/rules.rs
+++ b/src/rules.rs
@@ -109,34 +109,37 @@ pub(crate) async fn unset(interfaces: &Interfaces, rule: Rule) -> Result<(), any
                 dest_port,
             )
             .await?;
-            for iface in &interfaces.internal {
-                iptables::delete_forward_postrouting(
-                    rule.proto,
-                    iface.ip,
-                    iface.mask,
-                    interfaces.external.ip,
-                    rule.port,
-                    dest_ip,
-                )
-                .await?;
-            }
-            for iface in &interfaces.tunnel {
-                if interfaces
+            for iface in interfaces.internal.iter().chain(interfaces.tunnel.iter()) {
+                let is_nat_iface = interfaces
                     .nats
                     .iter()
-                    .any(|nat_iface| *nat_iface == iface.interface)
-                {
+                    .any(|nat_iface| *nat_iface == iface.interface);
+
+                let has_nat_subnet = interfaces.nats.iter().any(|nat_iface| {
+                    *nat_iface != iface.interface
+                        && interfaces
+                            .internal
+                            .iter()
+                            .chain(interfaces.tunnel.iter())
+                            .any(|other_iface| {
+                                *nat_iface == other_iface.interface
+                                    && other_iface.ip == iface.ip
+                                    && other_iface.mask == iface.mask
+                            })
+                });
+
+                if is_nat_iface {
                     iptables::delete_forward_prerouting(
                         rule.proto, iface.ip, iface.mask, rule.port, dest_ip, dest_port,
                     )
                     .await?;
-                } else {
+                } else if !has_nat_subnet {
                     iptables::delete_forward_postrouting(
                         rule.proto,
                         iface.ip,
                         iface.mask,
+                        dest_port,
                         interfaces.external.ip,
-                        rule.port,
                         dest_ip,
                     )
                     .await?;
@@ -192,34 +195,37 @@ pub(crate) async fn apply(interfaces: &Interfaces, rule: Rule) -> Result<(), any
                 dest_port,
             )
             .await?;
-            for iface in &interfaces.internal {
-                iptables::forward_postrouting(
-                    rule.proto,
-                    iface.ip,
-                    iface.mask,
-                    interfaces.external.ip,
-                    rule.port,
-                    dest_ip,
-                )
-                .await?;
-            }
-            for iface in &interfaces.tunnel {
-                if interfaces
+            for iface in interfaces.internal.iter().chain(interfaces.tunnel.iter()) {
+                let is_nat_iface = interfaces
                     .nats
                     .iter()
-                    .any(|nat_iface| *nat_iface == iface.interface)
-                {
+                    .any(|nat_iface| *nat_iface == iface.interface);
+
+                let has_nat_subnet = interfaces.nats.iter().any(|nat_iface| {
+                    *nat_iface != iface.interface
+                        && interfaces
+                            .internal
+                            .iter()
+                            .chain(interfaces.tunnel.iter())
+                            .any(|other_iface| {
+                                *nat_iface == other_iface.interface
+                                    && other_iface.ip == iface.ip
+                                    && other_iface.mask == iface.mask
+                            })
+                });
+
+                if is_nat_iface {
                     iptables::forward_prerouting(
                         rule.proto, iface.ip, iface.mask, rule.port, dest_ip, dest_port,
                     )
                     .await?;
-                } else {
+                } else if !has_nat_subnet {
                     iptables::forward_postrouting(
                         rule.proto,
                         iface.ip,
                         iface.mask,
+                        dest_port,
                         interfaces.external.ip,
-                        rule.port,
                         dest_ip,
                     )
                     .await?;
diff --git a/src/startup/preload.rs b/src/startup/preload.rs
index 348bbef..4c21871 100644
--- a/src/startup/preload.rs
+++ b/src/startup/preload.rs
@@ -198,6 +198,52 @@ fn filter(interfaces: &Interfaces) -> String {
 
     // FORWARD: Forwarding traffic across interfaces
 
+    for nat_iface in &interfaces.nats {
+        if let Some(iface) = interfaces
+            .internal
+            .iter()
+            .chain(interfaces.tunnel.iter())
+            .find(|iface| iface.interface == *nat_iface)
+        {
+            filter += &format!(
+                "-A FORWARD -i {natif} -d {natip}/{natmask} -j ACCEPT\n",
+                natif = iface.interface,
+                natip = iface.ip,
+                natmask = iface.mask,
+            );
+        }
+
+        for iface in interfaces.internal.iter().chain(interfaces.tunnel.iter()) {
+            let is_nat_iface = *nat_iface == iface.interface;
+
+            let has_nat_subnet = interfaces
+                .internal
+                .iter()
+                .chain(interfaces.tunnel.iter())
+                .any(|other_iface| {
+                    *nat_iface == other_iface.interface
+                        && other_iface.ip == iface.ip
+                        && other_iface.mask == iface.mask
+                });
+
+            if !is_nat_iface && !has_nat_subnet {
+                // Accept packets over NAT'd tunnel interfaces from pre-existing connections
+                filter += &format!(
+                    "-A FORWARD -i {natif} -o {intif} -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT\n",
+                    natif = nat_iface,
+                    intif = iface.interface,
+                );
+
+                // Reject packets over NAT'd tunnel interfaces
+                filter += &format!(
+                    "-A FORWARD -i {natif} -o {intif} -j REJECT --reject-with icmp-port-unreachable\n",
+                    natif = nat_iface,
+                    intif = iface.interface,
+                );
+            }
+        }
+    }
+
     // Accept packets over tunnel interfaces
     for iface in &interfaces.tunnel {
         filter += &format!(
@@ -273,13 +319,27 @@ fn nat(interfaces: &Interfaces) -> String {
     );
 
     for nat_iface in &interfaces.nats {
-        for internal in &interfaces.internal {
-            nat += &format!(
-                "-A POSTROUTING -s {intip}/{intmask} -o {natiface} -j MASQUERADE\n",
-                intip = internal.ip,
-                intmask = internal.mask,
-                natiface = nat_iface,
-            );
+        for iface in interfaces.internal.iter().chain(interfaces.tunnel.iter()) {
+            let is_nat_iface = *nat_iface == iface.interface;
+
+            let has_nat_subnet = interfaces
+                .internal
+                .iter()
+                .chain(interfaces.tunnel.iter())
+                .any(|other_iface| {
+                    *nat_iface == other_iface.interface
+                        && other_iface.ip == iface.ip
+                        && other_iface.mask == iface.mask
+                });
+
+            if !is_nat_iface && !has_nat_subnet {
+                nat += &format!(
+                    "-A POSTROUTING -s {intip}/{intmask} -o {natiface} -j MASQUERADE\n",
+                    intip = iface.ip,
+                    intmask = iface.mask,
+                    natiface = nat_iface,
+                );
+            }
         }
     }