"In the last couple of weeks, I have had a number of
people ask me to consider a small side trip in this series. Classic
wisdom says you do not turn on any network services you do not
need, and, in past articles, I have explained how services are
turned on and off through your /etc/inetd.conf file. The problem,
as one reader pointed out, is that after he upgraded his system to
Red Hat 7.1, inetd appeared to be gone, replaced with something
called xinetd. Worse, things weren't quite working the way he
expected--after upgrading to Red Hat 7.1, he noticed that he could
no longer log on from his home clients and /etc/inetd.conf was
gone. Since you, the readers, are my raison d'être, I will
take some time from this discussion of network monitoring to cover
xinetd. Besides, as it turns out, we do a little monitoring here as
well.
On one level, xinetd does exactly the same things as inetd. I
have often compared inetd's role to that of the telephone operator
Lily Tomlin played way back when. Essentially, you call in to the
operator (inetd), ask for the party you wish to speak to (TCP port
or service), and, if all goes well (TCP wrappers allow you in), the
operator connects you. But if it's simply a question of asking for
a service and being connected, then why, you may ask, is inetd
being replaced by xinetd? The answer is the same reason we want to
keep an eye on what is happening on our networks: security.
xinetd features a number of enhancements over good old inetd,
including extensive logging capabilities, limits on incoming
connections (to prevent denial of service attacks), flexible access
control for both local and remote connections, and much more (as
they say on TV). Configuring xinetd to perform all this magic
starts in the /etc/xinetd.conf file, where definitions for various
services are broken up into paragraphs with this format:"
