I've been setting up a shared Drupal hosting environment on an Ubuntu Server box, and just about everything is running great. Drupal's running, MysQL is running, and everything feels nice and fast.
But, the server can't see itself on the network. It can't even ping itself (via 127.0.0.1, localhost, or either of the domains pointing to the box). It can ping other boxes, though. It can't curl or wget or lynx any of the sites on itself. It can't telnet to its own services (which makes setting up mail services etc... a bit tricky).
The bizarre thing is, I can have full access to the services on that box remotely. SSH, FTP, ping, HTTP, etc... are all up and running, and respond normally to requests from off-machine.
None of that would be fatal, but the result of not being able to even curl a URL on the same box, means I can't run a script to automatically run cron.php on all Drupal sites.
I'm not sure what might need tweaking to enable the box to see itself over TCP/IP. I've checked in /etc/hosts, I've checked apache2 configs (nothing is rejecting from localhost).