This is even simpler to do than direct queries; just use the -broadcast option on the
X server command line:
blue$ X :8 -broadcast
The X server will perform a XDMCP broadcast using UDP and present a session
authentication prompt from the first server that responds.
This approach is particularly useful for load balancing. You can set up a bank of
servers with identical services and files (typically sharing the home directories using
NFS) and configure all of your users to connect using XDMCP broadcasts. Available
13.6
13.6 Accessing a Remote Session from a List of Available Sessions 179
servers only will respond; any server that is down or heavily loaded will not respond
to broadcast requests.
The downside to this approach is that every X server will broadcast an XDMCP
query, and every XDMCP server will respond. If you have 1,000 X servers and 50
XDMCP servers and the desktops are all turned on between 8:55 and 9:05 in the
morning, there will be 1,000 broadcast queries and up to 50,000 replies in a 10-
minute period. That would not be overwhelming to most networks but it is a significant
amount of traffic.
13.6 Accessing a Remote Session from a List
of Available Sessions
There is a compromise approach between direct XDMCP queries (Section 13.
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