network administration

list open ports

To list the ports that programs are using on your machine, simply issue this command:

netstat -a

open connections to your machine

To see the connections open from programs on your machine to places on the Internet, issue the following command:

netstat -p --inet

portscan a remote host

If you're interested to see how outsiders might try to check out your network, you can portscan it with 'nmap'.

nmap -sS -O -v 192.168.0.58

A couple of caveats:

• You can only do this as root
• You shouldn't do this against a remote host. This is often seen as prelude to an attack and you will most likely get complaints.

route to a virtual host

At times, you might need your one machine to masquerade or appear as different IP addresses. You might be developing multiple websites and can configure Apache to have virtual hosts with these IP addresses, for example. To create virtual addresses on your machine, do the following:

route add -host 192.168.X.X dev eth0

Change X.X to suit your needs. This assumes your network card is eth0. To get rid of this virtual host, substitute del for add.

synch date with timeserver

It's important that your machine always know the time. For this, you should always synchcronize the date with one of the many public timesevers on the Internet. The best way to do this is to install the ntp daemon. But if you need a quick update, you can also use the program 'ntpdate'. It's fairly simple to update your system's clock:

ntpdate some.timeserver.org

For more information on timeservers, see the ntp home page: http://www.ntp.org/

Getting Connected

kppp for dial-up

If you want to connect to the Internet with a standard dial-up connection, kppp (part of the KDE desktop system) will almost always do the trick. If you haven't got a modem that only runs under Windows, kppp should get you on the Internet in no time.

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