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Monday, October 25, 2010

Convert DHCP network configuration to static IP

Type into a console and all your physical network devices will be listed:lshw -class network
If you only wish to know which interfaces eth0 / eth1 / wlan0 or rausb0are currently configured type ifconfig into the console and you’ll get all theconfiguration stuff about these network devices!
two-nics-one-static-ip-to-serve-as-dns (win7)
Source: Ubuntu Linux convert DHCP network configuration to static IP configuration
 how to change or convert DHCP network configuration to static configuration. After initial installation, he wanted to change network settings. Further, his system is w/o GUI system aka X Windows. Here is quick way to accomplish the same:
Your main network configuration file is /etc/network/interfaces
Desired new sample settings:
- Host IP address
- Netmask:
- Network ID:
- Broadcast IP:
- Gateway/Router IP:
- DNS Server:
Open network configuration file
$ sudo vi /etc/network/interfacesOR$ sudo nano /etc/network/interfaces
Find and remove dhcp entry:
iface eth0 inet dhcp
Append new network settings:
iface eth0 inet static
Save and close the file. Restart the network:
$ sudo /etc/init.d/networking restart

Task: Define new DNS servers

Open /etc/resolv.conf file
$ sudo vi /etc/resolv.conf
You need to remove old DNS server assigned by DHCP server:

Save and close the file.

Task: Test DNS server

$ host

Network command line cheat sheet

You can also use commands to change settings. Please note that these settings are temporary and not the permanent. Use above method to make network changes permanent or GUI tool as described below.

Task: Display network interface information

$ ifconfig

Task: Take down network interface eth0 / take a network interface down

$ sudo ifconfig eth0 downOR$ sudo ifdown eth0

Task: Bring a network interface eth0 up

$ sudo ifconfig eth0 upOR$ sudo ifup eth0

Task: Change IP address and netmask from command line

Activate network interface eth0 with a new IP ( / netmask:
$ sudo ifconfig eth0 netmask up

Task: Display the routing table

$ /sbin/routeOR$ /sbin/route -nOutput:
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
localnet        *        U     0      0        0 ra0    *        U     0      0        0 eth0    *        U     0      0        0 eth1
default         UG    0      0        0 ra0

Task: Add a new gateway

$ sudo route add default gw

Task: Display current active Internet connections (servers and established connection)

$ netstat -nat

Task: Display open ports

$ sudo netstat -tulpOR$ sudo netstat -tulpn

Task: Display network interfaces stats (RX/TX etc)

$ netstat -i

Task: Display output for active/established connections only

$ netstat -e
$ netstat -te
$ netstat -tue
  • -t : TCP connections
  • -u : UDP connections
  • -e : Established

Task: Test network connectivity

Send ICMP ECHO_REQUEST to network hosts, routers, servers etc with ping command. This verifies connectivity exists between local host and remote network system:
$ ping router
$ ping
$ ping

Task: Use GUI (Graphical Configuration) network Tool

If you are new, use GUI configuration tool, type the following command at terminal:
$ network-admin &
Above command is Ubuntu's GUI for configuring network connections tool.

Final tip - Learn how find out more information about commands

A man page is your best friend when you wanted to learn more about particular command or syntax. For example, read detailed information about ifconfig and netstat command:
$ man ifconfig
$ man netstat

Just get a short help with all command options by appending --help option to each command:
$ netstat --help
Find out what command is used for particular task by searching the short descriptions and manual page names for the keyword:
$ man -k 'delete directory'
$ apropos -s 1 remove
Display short descriptions of a command:
$ whatis rm
$ whatis netstat
Linux offers an excellent collection of utilities, which can be use to finding the files and executables, remember you cannot memorize all the commands and files ;)
one small problem… if you edit /etc/resolv.conf directly, the next time you ifdown or ifup an interface or reboot for that matter your settings are lost. In Ubuntu the resolv.conf is generated each time you up/down an interface. So unless you removed the resolvconf package which is generally installed by default, you need to add proper dns- entries to the /etc/network/interfaces file to make changes permanent. eg:
iface eth0 inet static
# dns-* options are implemented by the resolvconf package, if installed

NetworkManager is fine for varying wlan configurations. This guide gives a sleek way to configure a static network. Afterwards you can
apt-get –purge remove network-manager knetworkmanager network-manager-gnome dhcdbdto get rid of unnecessarily runnig daemons.
About dns-nameservers: if you have >1 dns servers they must be in 1 line separated by spaces. But not in 2-3 lines (it will hangup network startup script at all) !
I think only dhclient updates resolv.conf, look like ubuntu has some additional scripting at /etc/rc.d/*. On a side note, you can write protect resolv.conf
sudo chattr +i /etc/resolv.conf
man chatt
I have two NIC cards in my Blade server. I have an Ethernet cable that comes from the router plugged into one of the NIC cards (that works and provides internet access for the blade server running Ubuntu 8.04). What I want to do since my second Ethernet cable is very short, is connect one end of the short cable to the second NIC card on the Blade server, and connect the other end of the short cable to the NIC card on my Windows Server 2003 so I can access the internet from the Windows machine. How do I go about getting the Windows server to access the internet? What configurations do I need to do on the Blade server and Windows server to make everything work? Your help is greatly appreciated. Thx
setup ip_forward to on
echo “1″ > /proc/sys/net/ipv4/ip_forward
and setup POSTROUTING, MASQUERADE to CARD2 that will share net to win
/sbin/iptables -t nat -A POSTROUTING -o eth0 -s CARD2IPHERE -j MASQUERADE

edit /etc/resolv.conf and add nameserver as follows:

This is for second ip
sudo vi /etc/network/interfaces
auto eth0:1
iface eth0:1 inet static
After entering all the details you need to restart networking services using the following command
sudo /etc/init.d/networking restart
sudo apt-get install resolvconf, and edit /etc/resolvconf/* settings

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