• A third-party server (the relay) acts as an intermediary between two devices that want to communicate but can’t connect directly (often due to firewalls or NAT). One example is the Secure Tunneling Server, Email Routing and Socat Relay etc


  • Both devices establish a connection to the relay server
  • The relay server coordinates the data flow between the devices, even if they can’t “see” each other directly on the network

Bridge of Differences

Can be used to connect networks that use different Network Protocol, extending the range of a network

Socat Relay

  • The command below relays TCP from a local machine Network Port to a remote network port running on TCP. The command creates a new Process (进程) for new connection on localhost:<LOCAL_PORT_NUMBER>, incoming requests are all port forwarded to the <REMOTE_ENDPOINT>:<REMOTE_PORT_NUMBER> over TCP
  • We can change the Network Protocol used on both sides, socat acts as a bridge
# -d -d enables debug mode
# TCP-LISTEN:<PORT_NUMBER>,fork forks a new process for each incoming connection


Socat is very slow compared to SSH Local Port Forwarding for some reasons. Let me know if you know why :)