Thanks for the explanation. Do I need port 177 only for XDMCP-capable
servers? I'm using the freeware MI/X on an internal Windows box for most
of my access, and this server doesn't talk XDMCP.
Also, I just upgraded to RH6.1, which replaced xdm with gdm. Can gdm be
configured to manage a non-XDMCP external X server? With xdm, I added a
"foreign" entry for my Windows box in the xdm-config file. What would be
the equivalent in gdm, if any?
> >> > It looks like xdm from XFree86 uses port 1024, or whatever unrestricted
> >> > port is the first available when xdm starts. This socket is then
> >> > inherited by all children of xdm, ie. shells and user programs. What is
> >> > xdm using this port for? I expect I need to firewall that port on my
> >> > external interface, as I do now with port 6000.
> >> Insert the line
> >> DisplayManager.requestPort: 0
> >> to /etc/X11/xdm/xdm-config
> >What does that do? I looked at "man xdm" and it says that requestPort is
> >the port to listen on for incoming XDMCP messages, and defaults to 177.
> >Why would setting it to 0 make xdm stop listening on port 1024?
> True, the requestPort resource defaults to 177, and sets the UDP port
> which xdm listens on for requests. Setting requestPort to zero disables
> this UDP port. But it also disables xdm's TCP port, which typically is
> on port 1024. Doing this, you lose the ability to have remote X server
> displays connect to your xdm, but will not affect controlling the local
> X server.
> Back to the original question. TCP port 1024 (actually, the first
> unreserved port available when xdm starts) is used by xdm to talk
> to chooser. Xdm starts chooser, then waits for chooser to tell it
> what host you picked. Chooser talks back to xdm through that port.