![]() ![]() However, localtunnel, ngrok, and telebit all have the ability to use tls servername indicator (SNI) instead of relying on port numbers. The initial explanation I gave using tcp ports, because it's easy to understand. See for long details Sidenote/Rant: Ports vs TLS SNI Likewise, when the remote responds to the relay, it has to include that information so that the relay knows which client the data packet is responding to. That info could be sent exactly before or append to each data packet that's routed. It needs to be something very similar to HAProxy's The PROXY Protocol, but works for non-local traffic as well. your computer) do is place a header in front of all data that is to be received by the client. (tcp 5678) (tcp 1234) Įssentially what the relay (i.e. Incoming client - Forwards To -> remoteīoth connections are "incoming" connections, but the remote connection on the "south end" is authorized to receive traffic coming from another incoming source (without some form of authorized session anyone could claim use of that port or address and hijack your traffic). Incoming client - MATCHES -> ALL_INCOMING However, the clients (such as browsers, netcat, or other user agents) that connect to you actually also initiate requests with the relay. ![]() So imagine that the relay (the localtunnel proxy in your case) uses port 7777 to receive traffic from "remotes" (like your computer) and your socket number (randomly chosen source address on your computer) is 1234: Devices: (tcp 1234:7777) When you run a "remote" (telebit, ngrok, and localtunnel all work nearly the same in this regard), it's actually your computer that initiates the request. How does a remote client access the server on my localhost? 1. The magic that you're curious about happens in two places: the remote socket and the multiplexer. I'm the author of Telebit, which provides service with similar features to what ngrok, localtunnel, and libp2p provide (as well as open source code for both the remote/client and relay/server to run it yourself).Īlthough I don't know the exact internals of how localtunnel is implemented, I can give you an explanation of how it's generally done (and how we do it), and it's most likely nearly identical to how they do it. Slides: How localtunnel, ngrok, and Telebit work (Long Answer) ![]() If you prefer a video preso, I just gave a talk on this at UtahJS Conf 2018, in which I talk a little about all of the other potential solutions as well: SSH Socksv5 proxies (which you mentioned), VPN, UPnP, DHT, Relays, etc:Īccess Ability: Access your Devices, Share your Stuff web browsers) connect, the relay multiplexes the connections between remotes and clients by appending special headers with network information. ) acts as a multiplexing proxy and when Clients (i.e. the localtunnel software on your computer) initializes the connection to the Relay (i.e. Is these understanding correct? If yes then what I don't understand is that how these server has access to some localhost running on my computer? How it perform request to it? What I'm missing here? Here is the code which I referred. So basically it's works like a proxy server. These services have a server which is publicly available, which generates different URLs, and when we hit that URL, It forward the request to localhost corresponding to that URL. I've tried reading code from it's github repository and what I understood is: It functions pretty much exactly like an SSH tunnel, but doesn’t require that you have a server. There services (localtunnel for example) creates a tunnel from their server back to port 3000 on your dev box. ![]() Which basically does routing from publicly available server to our localhost using SSH.īut I wonder how the service like 'LocalTunnel' works? In above article it's written as following: For that I've read a method of port forwarding using SSH. I want to understand how my local IP address (localhost) can be exposed to Internet. ![]()
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