Here are some helpful kwikis for running or using Linux with computer networks.

Be sure to also check the ArchLUG Kwiki page for kwikis that may be specific to your distribution of Linux.

Checking your bandwidth

http://www.2wire.com/ (ADSL: 1307.7 Kbps)
http://www.bandwidthplace.com/speedtest/ (ADSL: 1.2 Mbps)
http://www.pcpitstop.com/internet/Bandwidth.asp (ADSL: 1521 Kbps)

Monitoring Missouri Research and Education Network (MOREnet)

The Missouri Research and Education Network ( MOREnet) provides Internet connectivity, access to Internet2, technical support, videoconferencing services and training to Missouri's K-12 schools, colleges and universities, public libraries, health care, state government and other affiliates.

Real-World VPN Tunnels

For SSH tunnels, see SSH Tunnels
For GRE ( IPsec) tunnels, see GRE Tunnels

SPF - Sender Permitted From

From http://spf.pobox.com/

cuts spam and
stops email address forgery
when domain owners designate sending mail exchangers in DNS, so that
SMTP servers can distinguish legitimate mail from spam
by verifying sender domain against client IP
before any message data is transmitted.

SMTP has a security hole: any connecting client can assert any sender address. This flaw has been exploited by spammers to forge mail. Close the hole, and we can easily block spammers by sender domain.

I am a system administrator. How do I implement SPF?

http://spf.pobox.com/forsysadmins.html

I am a manager. Give me the executive summary.

http://spf.pobox.com/execsumm.html

Port forwarding using netcat and inetd

This involves setting up a listening 'netcat' ( ArchLUG - LinuxByExample : netcat ) as the application, and uses 'inetd' ( ArchLUG - LinuxByExample : inetd ) to bind it to a specific port and then forwarding the connection onwards to the ip and/or port where you want it to go. The configuration entry for 'inetd' looks something like this:

service geofwd
{
  flags = REUSE
  socket_type = stream
  wait = no
  user = root
  server = /usr/bin/nc
  server_args = 192.168.124.38 1005
  log_on_failure += USERID
}

If you use SSH from a GUI, you might like the following "launcher" applet for KDE, KSSH: http://kssh.sourceforge.net/. See also ArchLUG - LinuxByExample : ssh

Getting IP addresses from `ifconfig`

You can use 'ifconfig' to lookup IP addresses bound to your computer. If you do not want to search the output from ifconfig, use the following command to get just the IP listing:

ifconfig | awk '/inet/{print $2}' | awk -F: '{print $2}'

Whois Services

ARIN - American Registry for Internet Numbers

ARIN Whois

AfriNIC - African Network Information Center

AfriNIC Whois - Not operational

APNIC - Asia Pacific Network Information Center

APNIC Whois

LACNIC- Latin American and Caribbean Internet Addresses Registry

LACNIC Whois

RIPE - Réseaux IP Européens

Q: How do I find the technical and/or administrative contacts for a website?

I've tried 'nslookup' ( ArchLUG - LinuxByExample : nslookup ), but it only returns the ip of the server.

A: Use 'whois' ( ArchLUG - LinuxByExample : whois ), like this:

whois -h whois.arin.net website.you.are.looking.up

Depending on where it is located, you might have to follow that with some more whois commands to get more details.

How to setup your own DNS root server

Static route the 13 root server IPs to your own nameserver. Then you can run an unmodified copt of the legacy root zone on your own nameserver and the US government root servers can be backhoed or DDOS'd and you wouldn't even notice.

ISP's are starting to figure this out, especiallly ones with expensive longhaul connections.

Or, you can modify your nameserver to declare youtself primary for the root zone (which you've dutifully downloaded) and edit out the declarations for "." in the legacy root zone.

Or you can use the ORSC root zone. If it's good enough for two ICANN board members, it's good enough for you.

Whatever you do, for God's sake dump bind and use DJBDNS. It really is so much better it's just not funny.

User restarts for your network interfaces

Just make this little script executable and place it somewhere in everyone's path. I recommend /usr/local/bin/

#!/bin/sh
kdialog --title 'Internet Restart' --yesno 'Do you want to restart your internet connection?'
result=$?
if [ 0 ==  $result ]; then
  kdialog --passivepopup 'Resetting Internet Connection ...' 2 &
  sudo /sbin/ifdown eth0
  sleep 2
  sudo /sbin/ifup eth0
  kdialog --msgbox 'Internet Connection reset.'
fi

Then, add the following to your /etc/sudoers file.

%users ALL=NOPASSWD:/sbin/ifdown eth0
%users ALL=NOPASSWD:/sbin/ifup eth0

Now, for the users, you can simply create a shortcut to the script, give it whatever icon, and they can restart the network interface any time they like.

I have found this particularly useful on a system where the NE2000 (ne2k_pci) module in the 2.6 kernel seems to "lose" the interface after inactivity.

NetworkKwikis