I can't seem to find what config is missing. It use to work this way there might be something change in cygwin. I had similar setup which was always working. I have make sure that firewall on windows is turn off. [raza@mytest]$  export DISPLAY=:0.0 [raza@mytest]$  xhost + access control disabled, clients can connect from any host [raza@mytest]$  export DISPLAY=localhost:0.0 [raza@mytest]$  xhost + xhost:  unable to open display localhost:0.0 [raza@mytest]$   xauth list mytest/unix:0  MIT-MAGIC-COOKIE-1  7ab7e0be4cf96102784fb9c3bb9f0d3b mytest:0  MIT-MAGIC-COOKIE-1  7ab7e0be4cf96102784fb9c3bb9f0d3b mytest:0  MIT-MAGIC-COOKIE-1  7ab7e0be4cf96102784fb9c3bb9f0d3b [raza@mytest]$   telnet localhost 6000 Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection refused
Error: Can't open display: localhost:0.0 but :0.0 works
cygwin