$ xlogo
Error: Can't open display: localhost:10.0

ssh -Y remotehost -p 2500
ssh -X remotehost -p 2500

debug1: channel 1: new [X11 inet listener]
debug1: channel 2: new [X11 inet listener]

$ echo $DISPLAY
localhost:10.0

$ netstat -l | grep 6010

tcp        0      0 ip6-localhost:6010      *:*                 LISTEN
tcp6       0      0 ip6-localhost:6010      [::]:*              LISTEN

Warning: No xauth data; using fake authentication data for X11 forwarding.

remotehostname/unix:14  MIT-MAGIC-COOKIE-1  70f068c8dd2431088bcxxxxxxxxx
remotehostname/unix:13  MIT-MAGIC-COOKIE-1  be500209ccb9fb769eexxxxxxxxx
remotehostname/unix:12  MIT-MAGIC-COOKIE-1  01fc30e4887501602ebxxxxxxxxx
remotehostname/unix:11  MIT-MAGIC-COOKIE-1  d04f849725f71070095xxxxxxxxx
remotehostname/unix:10  MIT-MAGIC-COOKIE-1  42e99c898ef9aa295b4xxxxxxxxx

127.0.0.1 localhost remotehostname localhost.localdomain
::1 localhost ip6-localhost ip6-loopback


X11 connection rejected because of wrong authentication.
Error: Can't open display: localhost:10.0

if [ -n "$DISPLAY" ]; then
  echo "DISPLAY: $DISPLAY" >&2
  if read proto cookie; then
    if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
      echo add unix:`echo $DISPLAY | cut -c11-` $proto $cookie
    else
      echo add $DISPLAY $proto $cookie
    fi | $HOME/.ssh/xauth.wrapper -q -
  fi
fi