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Opera Unite installs a web server on the user's computer and allows it to be accessible with end-to-end connectivity to the client - without port forwarding in the case of those behind routers. From what I have looked around, it does it by the NAT Traversal methods in the cases where its possible, otherwise uses a proxy server. This tells how they do it.

Could anybody throw more light on how is this possible? It is more like a peer-to-peer connection if they are using the NAT Traversal methods like STUN, TURN and ICE.

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Opera Unite attempts to set up a port-forward through the use of certain UPnP/IGD calls. (Home) routers that support UPnP port-traversal configuration will just set up the port forward. Opera Unite's central servers then handles the name resolution issues.

Any enterprise router worth it's salt doesn't enable IGD.

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Ok UPnP is one method. But I dont think that it would be enabled in all the cases. It mentions NAT Traversal. Could it possibly be using hole punching? Is hole punching a possible method for accessing a server (that is behind a router - without port forwarding) through a web browser? – angad Dec 13 '10 at 17:16
@Anagad I'm pretty certain that if the browser-based Unite can't get a hole punched by way of UPnP/IGD, it falls back to proxying through the Opera servers themselves. It connects to the Opera Unite servers and any client traffic directed at that particular browser-Unite service gets funneled down the already-open connection. And you're right UPnP/IGD is NOT enabled in all cases, which is why they have the proxy-fallback. – sysadmin1138 Dec 13 '10 at 17:24

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