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Hi, I have setup a tunnel from server A to server B across WAN by running "ssh -l user_X -L port_A:server_B:port_B server_C -N". Server B is in a private network, so I have to establish the tunnel via server C, which is in the same LAN with B but has a public IP. The problem is, every time I start the tunnel on server B, the tunnel process will die nearly two hours later. And it always g...