[Fallback](https://xtls.github.io/config/features/fallback.html) feature enables an inbound to forward the incoming request to another inbound or another process.
Nginx is used to serve a decoy website to avoid active probing. It's also used to route gRPC traffic(grpc_pass).
The Vless-TCP-XTLS is the HTTPS entrypoint. For every incoming request after doing TLS-Termination, based on the **Path**, **SNI** or **ALPN type**, the request is passed to another inbound(sub-config). For example:
* In case of **ALPN=HTTP2**, it's first passed to **@trojan-tcp**. In trojan-tcp, if if it's not a valid request(for example the trojan password is wrong), another fallback is set, to once more pass the request to Nginx HTTP2 Unix Domain Socket and a decory website is served. When the request is using HTTP2, it could also be gRPC, so that is also checked in Nginx. This is how a VMESS-gRPC request is processed:
* **Your Domain** in both and server (for fallbacks section) and client configs.
*`sed -i 's/example.com/YOUR_DOMAIN/g' *`
*`sed -i 's/behindcdn.com/YOUR_CDN_DOMAIN/g' *` (if you don't have one, remove the config for cdn domain from inbounds[0].streamSettings.tlsSettings.certificates in server.json)
* **(Optional)** Path of all sub-configs. For **Websocket**-->`wsSettings.path`, for **TCP**-->`tcpSettings.header.request.path`, for **gRPC**-->`grpcSettings.serviceName` and for **H2**-->`httpSettings.path`.
* **(Optional)** The SNIs of H2 fallbacks (`inbounds[0].settings.fallbacks.[].name`) could also be changed but they should be consistent between client and server. (Read the notes on HTTP2 inbounds)
* For a little better performance, a DNS Cache could be setup (on 127.0.0.53 in this case) and used for resolving DNS queries. To enable xray to use it uncomment the corresponding rule from the `routing.settings.rules` in server.json.
* Multiple domains could be used at the same time, including domains behind cloudflare CDN. (For cloudflare, make sure websocket and gRPC are enabled in Network section). In this configuration these domains are **example.com** and **behindcdn.com**
* HTTP2 inbounds (Trojan-H2, Vless-H2, VMESS-H2 and ShadowSocks-H2)
* [HTTP2 Transport does not support fallback based on `path`](https://xtls.github.io/config/transports/h2.html#http-2). That's why SNI is used instead.
* It's possible to create a CNAME dns record for all the H2 SNIs and use that as the address of the client config without setting custom SNI on client but it's optinal.
* It is assumed that the **example.com** domain has a **wildcard certificate**. If it's **not** a wildcard certificate or if it's a self-signed certificate, then `streamSettings.tlsSettings.allowInsecure` in the **client configuration** must be `true`.
