(as root) A very good menu-driven setup for your network.
Check if you can contact another machine (give the machine's name or IP),
press C when done (without c, the command keeps
going). As all Linux commands, ping has options, including the
"ping of death" attack, when it seems you can ping some servers so they
die--try the the opitons -f and -s.
Show the kernel routing table.
(Three commands, use any.) Query your default domain name server (DNS)
for an Internet name (or IP number) host_to_find. This way you
can check if your DNS works. You can also find out the name of the host
of which you only know the IP number.
Have a look how your messages trace to host_to_trace (which
is either a host name or IP number).
(as root) A powerful and nice tool that combines the functionality of
the older ping and traceroute (RH7.0)
Status of a networked MS Windows machine (with an NetBIOS name).
This command is an equivalent of Windows nbtstat command.
-F -p m
(for RH5.2, see the next command for RH6.0) Set up the firewall IP forwarding
policy to masquerading. (Not very secure but simple.) Purpose: all computers
from your home network will appear to the outside world as one very busy
machine and, for example, you will be allowed to browse the Internet from
all computers at once.
1 > /proc/sys/net/ipv4/ip_forward
ipfwadm-wrapper -F -p deny
ipfwadm-wrapper -F -a m -S xxx.xxx.xxx.0/24 -D 0.0.0.0/0
(three commands, RH6.0). Does the same as the previous command. Substitute
the "x"s with digits of your class "C" IP address that you assigned
to your home network. See FAQ-masquerading for
-P forward DENY
ipchains -A forward -s xxx.xxx.xxx.0/24 -d 0.0.0.0/0 -j MASQ
(two commands, RH7.0). Same as previous commands, but works under
List all firewall rules. Use to check if your firewalling setup works.
Linux kernel 2.4.x uses new firewalling "iptables". The above example
lists the firewall rules.
(as root, in Xterm). A GUI for building your custom firewall.
(as root) Display info on the network interfaces currently active
(ethernet, ppp, etc). Your first ethernet should show up as eth0, second
as eth1, etc, first ppp over modem as ppp0, second as ppp1, etc. The "lo"
is the "loopback only" interface which should be always active. Use the
options (see ifconfig --help) to configure the interfaces.
(/sbin/ifup to run as a user) Startup a network interface. E.g.:
Users can start up or shutdown the ppp interface only when the permission
is given in the ppp setup (using netconf ). To start a ppp interface
(dial-up connection), I normally use kppp available under the KDE "K"
menu (or by typing kppp in an X-terminal).
Restart the network using its normal initialization script (the same which
is used during bootup). Useful if you just have manually made changes
to your network configuration. Any other service listed in init.d
can be stopped, started, or restarted in a similar way (call the script
with an options stop, start or restart).
(/sbin/ifdown to run it as a user). Shut down the network interface.
E.g.: ifdown ppp0 Also, see the previous command.
Displays a lot (too much?) information on the status of your network.
(as root, in X windows if you wish the nice gtk-based interface). Network
diagnostic tool combining the capabilities of traceroute and ping.
Comes with RH7.0.
Map the ports on the machine with ip_number. REALLY useful
to establish the security of your network configuration as you can see
the opened ports. nmap is included on the RH7.0 "Linux PowerTools"
CD, as is a convenient GUI front end, "nmapfe". nmap can also do operating
system "fingerprinting". Normally, people (and their ISPs) don't like
their computer ports being scanned (they view it as possbily probing before
an attack) so they may complain if they find out--learn how to use nmap
on your own computers else you will soon hear from your ISP (the complaints
will go to them). How do I know this?
(as root, in Xterminal) Network analyzer--view the network trafic going
through your computer. Included on the RH7.0 "Linux PowerTools" CD.
Using ethereal may be unethical in some situations, and unauthorized use
in the workplace could be a fireable offence.
-i ppp0 -a -x
(as root) Print all the network traffic going through the first over-the-phone
interface (ppp0) as ascii and hexadecimal. Probably too much printout.
tcpdump is a rather raw tool and it can be useful for building
more "customized" tools for listening to/log what you need.
Next > 5.18