I've always used my Ubuntu desktop behind the security of a router with NAT, but there have been a few times when I've had to plug it directly into an active cable modem.
In general, what precautions I should be taking in situations when my computer is exposed to the internet like this for extended periods of time? Specifics that immediately come to mind are:
- Are there any default network services I might want to disable?
- Is there a need to modify the default firewall configuration?
- Should I be concerned about services using password authentication?
- What kind of logging can I do to be notified of unauthorized access?
I realize that questions like this are just the tip of the iceberg of expansive topics that entire professions are based upon, so let me make clear: What I'm looking for are a few straightforward recommendations of best practices or configuration changes that a desktop user would find useful in a default Ubuntu installation.