The goal of this project is to be able to use XDMCP through SSH or more generally through a TCP connection. Tunneling RDP or VNC is easy because these protocols only rely on a single TCP connection between the client and the server. On the contrary the XDMCP protocol requires UDP which can't be tunneled through a TCP connection. The simple tool `xdmcptunnel' adds the missing parts and handles the UDP stuff of XDMCP protocol.
This tool can be used when it is not possible to open a direct UDP connection between the XDMCP client and the target machine.
On the machine where the remote desktop will be displayed, an X server needs to be started.
Xnest -listen tcp -from 127.0.0.1 :5 &
On the machine whose desktop is accessed remotely, a small C program is executed. This program handles the XDMCP UDP negocitation and arranges for the X TCP traffic to be tunneled back to the client machine.
ssh -R 6005:127.0.0.1:6005 user@remote xdmcptunnel -d 5
XDMP is considered unsecure and is disabled by default. It is enabled by tuning the configuration of the display manager used.
XDMCP is enabled by editing the file /etc/lightdm/lightdm.conf, there should be a block named XDMCPServer in the file, looking like this :
#
# XDMCP Server configuration
#
# enabled = True if XDMCP connections should be allowed
# port = UDP/IP port to listen for connections on
# listen-address = Host/address to listen for XDMCP connections (use all addresses if not present)
# key = Authentication key to use for XDM-AUTHENTICATION-1 or blank to not use authentication (stored in keys.conf)
# hostname = Hostname to report to XDMCP clients (defaults to system hostname if unset)
#
# The authentication key is a 56 bit DES key specified in hex as 0xnnnnnnnnnnnnnn. Alternatively
# it can be a word and the first 7 characters are used as the key.
#
[XDMCPServer]
#enabled=false
#port=177
#listen-address=
#key=
#hostname=
To enable XDMCP change the block to :
[XDMCPServer]
enabled=true
port=177
listen-address=127.0.0.1
#key=
#hostname=
First step, start xnest and launch xdmcptunnel
Second step log on. Make sure to not log as the current user it won't work nothing will be displayed
The script rdp.sh starts a remote desktop.