Multiple IP addresses on One Interface

Interface aliasing allows one interface to have multiple IP addresses. This is useful when more than one server is to be visible via the Internet. Note that virtual hosts can support multiple Apache servers with a single IP address. Apache responds to the domain name supplied by the client in the HTTP header. In many other situations, one external IP is needed for each server using a port.

This /etc/network/interfaces text assigns three IP addresses to eth0. 

auto eth0
allow-hotplug eth0
iface eth0 inet static
    address 192.168.1.42
    netmask 255.255.255.0
    gateway 192.168.1.1

auto eth0:0
allow-hotplug eth0:0
iface eth0:0 inet static
    address 192.168.1.43
    netmask 255.255.255.0

auto eth0:1
allow-hotplug eth0:1
iface eth0:1 inet static
    address 192.168.1.44
    netmask 255.255.255.0

An alias interface should not have "gateway" or "dns-nameservers"; dynamic IP assignment is permissible.

The above configuration is the previous traditional method that reflects the traditional use of ifconfig to configure network devices. ifconfig has introduced the concept of aliased or virtual interfaces. Those types of virtual interfaces have names of the form interface:integer and ifconfig treats them very similarly to real interfaces.

Nowadays ifupdown uses ip utility from the iproute2 package instead of ifconfig. The newer ip utility does not use the same concept of aliases or virtual interfaces. However, it supports assigning arbitrary names to the interfaces (they're called labels). ifupdown uses this feature to support aliased interfaces while using ip.

Also, ifupdown supports specifying multiple interfaces by repeating iface sections with the same interface name. The key difference from the method described above is that all such sections are treated by ifupdown as just one interface, so user can't add or remove them individually. However, up/down commands, as well as scripts, are called for every section as it used to be.

This /etc/network/interfaces text assigns three IP addresses to eth0.

auto eth0
allow-hotplug eth0
iface eth0 inet static
    address 192.168.1.42
    netmask 255.255.255.0
    gateway 192.168.1.1

iface eth0 inet static
    address 192.168.1.43
    netmask 255.255.255.0

iface eth0 inet static
    address 192.168.1.44
    netmask 255.255.255.0

# adding IP addresses from different subnets is also possible
iface eth0 inet static
    address 10.10.10.14
    netmask 255.255.255.0

Additional information can be found on the http://www.shorewall.net/Shorewall_and_Aliased_Interfaces.html page.

How To Configure Wireless / WiFi Networking in Ubuntu via the Command Line (CLI)

How To Configure Wireless / WiFi Networking in Ubuntu via the Command Line (CLI)

There are a number of tutorials available on-line for sorting out WiFi in Ubuntu via the CLI, but most of them seem quite outdated, so I decided to do my own.

I did this on a minimal install of Ubuntu Lucid, so it is as up-to-date as possible. The PC I was using has no Windows Manager of Graphical Display Manager, just the good old terminal so all this is done via the CLI only. I did this using a USB WiFI dongle, but it should be the same whether you use an internal card or a USB card.

First, you need to install the relevant software. You need to have a wired connection at this point, otherwise this wont work.

sudo apt-get install wireless-tools wpasupplicant

If you are connecting to an open network, you wont need wpasupplicant. Next, you need to “bring up” (essentially this means activate) your WiFi interface. So, issue:

sudo ifconfig wlan0 up

Next, to make sure your wireless device is working as it should issue:

iwconfig

and then

sudo iwlist scan

This should show you some wireless networks as proof that the WiFi device is working, if something goes wrong here, then there is a problem with your device or driver and you need to get googling.
If you are accessing a secured network and you really should be, you need to access the correct version of your WiFi key. To get your key, issue this command:

wpa_passphrase YOURSSID YOURWIFIPASSWORD 

This will result in something that looks like this:

network={
ssid="YOURSSID"
#psk="YOURWIFIPASSWORD"
psk=fe727aa8b64ac9b3f54c72432da14faed933ea511ecab1 5bbc6c52e7522f709a
} 

You need to make a note of the long phrase after psk= (NOT #psk=) as this your WiFi password in hex format.
Next, you need to edit your interfaces file, so issue:

sudo nano /etc/network/interfaces

At the end of this file, you need to add your WiFi configuration. Here are the options you can add.

auto wlan0     #change this to the name of your WiFi interface
iface wlan0 inet dhcp     #this is normally fine, if you want a static IP address replace “dhcp” with “static”
netmask 255.255.255.0     #change this as appropriate for your network, this value is usually right
gateway 192.168.1.1     #change this as appropriate for your network
address 192.168.1.100     #only needed for a static IP address
dns-nameservers 192.168.1.1     #only needed for a static IP address
wpa-driver wext     #you shouldn’t need to change this
wpa-ssid YOURSSID     #just type the name of your SSID here
wpa-ap-scan 1     #if the name of your SSID is hidden usually, type 2 instead of 1
wpa-proto WPA    #if you use WPA1 type WPA, if you use WPA2 type RSN
wpa-pairwise CCMP     #if you use AES type CCMP, if you use TKIP type TKIP
wpa-group CCMP     #if you use AES type CCMP, if you use TKIP type TKIP
wpa-key-mgmt WPA-PSK     #usually WPA-PSK (if you share a key) but sometimes WPA-EAP (for enterprises)
wpa-psk YOURHEXKEYFROMABOVE     #the hex key that you generated earlier

Thus, since I am using a WiFi card that is identified as wlan0 and am connecting to a WPA1 AES encrypted network called MYPLACE that isn’t hidden without a static IP address, this is what I added:

auto wlan0
iface wlan0 inet dhcp
netmask 255.255.255.0
gateway 192.168.1.1
wpa-driver wext
wpa-ssid MYPLACE
wpa-ap-scan 1
wpa-proto WPA
wpa-pairwise CCMP
wpa-group CCMP
wpa-key-mgmt WPA-PSK
wpa-psk 71c81a844973ae7bb1243141e5caa7b6bb0e2d7eetcetcetc

Finally, comment out the top section so it looks like this:

#auto eth0
#iface eth0 inet dhcp

This stops your wired network from working. This helps to ensure there are no conflicts. Remember, if you want your wired network to work again, remove these two comments (the #).
Finally, save the file by pressing CTRL and X and then pressing Y to save to the file. Now, reboot and your network should come up. Yay!
Some people have found that this doesn’t always work, so the next thing to do is to edit the configuration file for the wpasupplicant program. Do this by issuing:

sudo nano /etc/wpa_supplicant.conf

Basically, you add pretty much the same information here as you did to the interfaces file, except without the wpa- part. So, my file looks like this:

ap_scan=1
ctrl_interface=/var/run/wpa_supplicant
network={
ssid="MYPLACE"
scan_ssid=0
psk=71c81a844973ae7bb1243141e5caa7b6bb0e2d7eetcetcetc
key_mgmt=WPA-PSK
proto=WPA
pairwise=CCMP
group=CCMP
}

As far as I am aware, the options are the same. So, edit this file as necessary, make sure you add the ctrl_interface and network={ at the beginning and the } part at the end. Save it and try restarting again. If it still doesn’t work, then kick your PC, wish you had installed Windows 7 instead and go off and do some Googling. You’ll find the answer on the Ubuntu forums and you’ll be happy again.

Best of luck!

Setup PPTP Server on Ubuntu 12.4 Server.

This guide has been tested with Ubuntu 12.4 Server.

Setup PPTP Server

First we need to install pptp server using apt-get 

# sudo apt-get install pptpd

Then we need to configure the pptpd.

# sudo nano /etc/pptpd.conf

Add server IP and client IP at the end of the file. You can add like below:

localip 192.168.0.1
remoteip 192.168.0.100-200

This sets up the PPTP server to use IP 192.168.0.1 while distributing the IP range 192.168.0.100 to 192.168.0.200 to PPTP clients. Change these as you wish as long as they are private IP addresses and do not conflict with IP addresses already used by your server.

Configure DNS servers to use when clients connect to this PPTP server

# sudo nano /etc/ppp/pptpd-options

Uncomment the ms-dns and add google like below or OpenDNS

ms-dns 8.8.8.8
ms-dns 8.8.4.4

Now add a VPN user in /etc/ppp/chap-secrets file.

# sudo nano /etc/ppp/chap-secrets

The column is username. Second column is server name, you can put “pptpd” in there. Third column is password. The last column is the IP addresses, you can put * to allow all IP.

# client        server  secret                  IP addresses
username * myPassword *

Finally start your server

# /etc/init.d/pptpd restart

Setup IP Forwarding

To enable IPv4 forward. Change /etc/sysctl.conf file, add forward rule blew.

# sudo nano /etc/sysctl.conf

Uncomnent the line

net.ipv4.ip_forward=1

Then reload the configuration

sudo sysctl -p

Add forward rule in iptables

# sudo nano /etc/rc.local

adding to the bottom just before the exit 0

iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE
iptables -A FORWARD -p tcp --syn -s 192.168.0.0/24 -j TCPMSS --set-mss 1356

This example is using 192.168.0 for its PPTP subnet. The second rule adjusts the MTU size :

You are done. Just reboot your server and you should be able to connect to using PPTPD and send all your traffic through this server.

Rip, copy a CD/DVD to ISO format.

Rip a CD/DVD to ISO format.

$ dd if=/dev/cdrom of=~/cdrom_image.iso

Rip a CD/DVD to ISO format.

An easy method to generate ISOs from CD/DVD media.

Alternatives

There are 2 alternatives

$ readom dev=/dev/scd0 f=/path/to/image.iso

Create a CD/DVD ISO image from disk.

Many like to use 'dd' for creating CD/DVD iso images. This is bad. Very bad. The reason this is, is 'dd' doesn't have any built-in error checking. So, you don't know if you got all the bits or not. As such, it is not the right tool for the job. Instead, 'reaom' (read optical media) from the wodim package is what you should be using. It has built-in error checking. Similarly, if you want to burn your newly creating ISO, stay away from 'dd', and use:

wodim -v -eject /path/to/image.iso

$ readcd dev= f=foo.iso

The only problem here is that there is no error checking or correction. The cdrecord package includes a command line tool called readcd that rips CDs to iso files quite nicely