So should you use this double NAT scenario and be happy with it? It highly depends on your equipment and your usage scenario. Most games and game consoles report this as the “ NAT status” of your router, using four broad categories of open, moderate, strict, and blocked, which aren't standardized either - each game vendor may use them for slightly different technical details. And the NAT behavior that happens in parallel isn't predictable either - every router has a slightly different method of deciding how to map addresses to ports on outgoing traffic. Unfortunately the firewall details aren't a fully standardized behavior. Many online games use tricks to get peer-to-peer data traffic of other players through your firewall(s) to your game client OpenWrt as gateway using either OpenWrt-device-built-in or external modemĬlients ↔ OpenWrt as gateway with NAT ↔ built-in/external modem (no NAT) ↔ Internet Look-out: OpenWrt as router in IPv6 only configuration + ISP routerĬlients ↔ OpenWrt router (no NAT) ↔ ISP router (no NAT) ↔ Internet OpenWrt as router with disabled NAT, additional routing rules in both routersĬlients ↔ OpenWrt router (no NAT) ↔ routing rules ↔ ISP router with NAT ↔ Internet OpenWrt as router in double-NAT configuration with Dualstack Lite on ISP sideĬlients ↔ OpenWrt router with NAT ↔ ISP router with DS-Lite NAT ↔ Internet OpenWrt as router acting in default cascaded router double-NAT configurationĬlients ↔ OpenWrt router with NAT ↔ ISP router with NAT ↔ Internet OpenWrt as router, OpenWrt router being "exposed host" in the ISP routerĬlients ↔ OpenWrt router with NAT ↔ ISP router with NAT + “exposed host” feature ↔ Internet OpenWrt as router and having an internet ISP device configured as modem-bridgeĬlients ↔ OpenWrt router with NAT ↔ ISP bridge (no NAT) ↔ Internet Since the OpenWrt device is our main concern, we'll refer to upstream and downstream connections relative to it: clients ↔ OpenWrt device ↔ ISP device ↔ Internet. Note that in all these examples, the OpenWrt device is assumed to be on the “inside” of the network, i.e. To deal with this double NAT problem and use IPv4 as flawlessly as possible, you need to choose how OpenWrt gets connected on its upstream side from several options. This double NAT scenario won't cause problems for basic tasks like browsing the internet, but it can cause problems when you are trying to host servers at home that you want to be reachable from the internet, or when doing peer-to-peer online gaming (which often uses the UDP protocol and does some funny firewall stuff called “ UDP hole-punching”). The problem of IPv4 is that if you simply add an additional IPv4 router to an existing router of your ISP (internet service provider), you will face a problem called double NAT - both the newly added router and the existing ISP-supplied router do NAT, resulting in your client data traffic being “NATed” twice before it reaches the internet. In the meantime for IPv4, act according to this how-to. In a few decades, when the whole world is fully IPv6 enabled devices, this won't be a problem anymore, as IPv6 strictly forbids NAT. → Alternatively, get familiar with OpenWrt first, then come back later and decide how to proceed.ĭouble NAT is an issue that exists solely with IPv4. Your device will act as a router in a cascaded double NAT scenario which will work just fine for normal internet access, so you don't have to do anything. → Just stop reading and use the default configuration for now. ![]() ![]() Are you an OpenWrt newcomer? Does this page with lots of technical network information seem scary? Are you worried that you don't know enough to make these decisions now?
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