FYI CentOS is Redhat Enterprise re-compiled from source RPMs with all the trademark stuff removed. It's good to play around with RHES for free before you need all the production-grade support etc.

Not sure why you are typing netstat -D. What would that normally do? netstat -n would work, that displays IP addresses instead of names. To get the same effect as netstat -t I guess you would use netstat -p <protocol>, on Redhat Linux -t restricts the protocol to TCP.

You're right, ifconfig -a does work as non-root however on Redhat the /sbin directory where it lives is not in a normal user's search path. Anyway, thanks for pointing that out to me as it is probably a safer command to work with.

Yes, arp is available on Redhat but is also in /sbin.
/sbin/arp -i eth0 -a
Seems to produce meaningful output.

Thanks for you help :-)