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--- advanced-firewall [2026/07/23 17:41] – [Firewall] Condense hogwild
+++ advanced-firewall [2026/09/30 12:59] (current) – [NAT] rs232
@@ Line 21: / Line 21: @@
  \\ **Enable TCP SYN cookies:  **uses "SYN cookies" to protect the router from SYN Flood attacks.
-This encodes information from the SYN packet into the (SYN/ACK) response-a standard method for preventing SYN floods. However, its limitations may cause issues with some old TCP/IP stacks. \\
+This uses a standard method for preventing SYN floods. It encodes information from the SYN packet into the (SYN/ACK) response. Its limitations may cause issues with some old TCP/IP stacks. \\
  \\
@@ Line 54: / Line 54: @@
 ===== NAT =====
-**NAT loopback:** lets LAN devices access each other via the router's WAN interface.
+**NAT loopback:** The NAT Loopback (Hairpinning) logic is implemented in the firewall subsystem (firewall.c) using iptables rules applied to the PREROUTING and POSTROUTING chains of the nat table.
-Also known as "Hairpinning", it's often used when connecting to the DDNS domain of your router via the LAN. These days, this setting is almost never needed. Also, it can create speed bottlenecks.
+\\
- \\
+. Disabled \\
+Under the Hood (iptables): FreshTomato omits loopback rules in the NAT chains.
+\\
+Behavior: When a local LAN client sends traffic destined for the router’s public WAN IP address (or DDNS domain name), the router receives it, sees that there is no active rule translating internal LAN traffic back into the LAN, and simply drops or rejects the traffic.
+\\
+Pros:
+- Lowest router CPU load and max throughput (zero extra NAT inspection or packet rewriting for LAN traffic).
+- Forces proper network boundary segregation.
+\\
+Cons:
+- LAN devices cannot access local servers using public domain names or public IP addresses nor the router admin interface on the WAN.
+\\
+\\
+. Forwarded Only (default) \\
+Under the Hood (iptables): FreshTomato generates rules that apply loopback translation only to traffic aimed at ports that are explicitly defined in the Port Forwarding rules.
+\\
+Matches LAN traffic destined for WAN_IP:PORT only if PORT exists in nat PREROUTING / port-forward tables. These are essentially ports you find defined under Port Forwarding.
+\\
+Behavior: If you forward port 8443 to an internal server at 192.168.1.10:443, a LAN device reaching out to [https://yourdomain.com:8443](https://yourdomain.com:8443) gets rewritten and looped back inside the LAN. However, if you try to reach [https://yourdomain.com:443](https://yourdomain.com:443) (a port with no active forward rule), it is rejected/dropped.
+\\
+Pros:
+- Security & Control: Prevents local LAN traffic from hitting closed or un-forwarded router ports via the external WAN identity.
+- Performance: Limits loopback processing overhead to explicitly required ports only.
+\\
+Cons:
+- Will not work for dynamic or non-forwarded services (e.g., UPnP-opened ports or DMZ configurations depending on implementation). It will not work for the router administration GUI called on its WAN interface from a LAN device.
+\\
+\\
+. All \\
+Under the Hood (iptables): FreshTomato inserts a blanket PREROUTING NAT rule matching all traffic coming from the LAN interface aimed at the WAN interface IP address, regardless of whether a port forward rule exists.
+\\
+Behavior: Any LAN connection sent to the WAN IP (only to the WAN IP, not the Internet!) is looped back to the router or LAN destination.
+\\
+Pros:
+- "It just works" convenience—applies to UPnP mapped ports, DMZ hosts, and all services without needing individual port forward rules. This is the only mode supporting the WAN router administration called from the LAN.
+\\
-  * All
+Cons:
-  * Forwarded Only
+- Performance Bottlenecks (minor): Every single piece of LAN-to-"WAN-IP" traffic runs through blanket SNAT/DNAT rule-matching cycles, bypassing hardware NAT/CTF (Cut-Through Forwarding) acceleration on supported chipsets. NOTE: this is to the WAN-IP not the Internet!
-  * Disabled
+- Unintended Loops/Routing Anomalies (rare): Can cause severe instability or packet loops when using dual routers, wireless bridges, or complex multi-subnets.
  \\

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