Debian Linux Configure Network Interface Cards – IP address and Netmasks

Posted on in Categories , , last updated January 27, 2014

How do I configure networking or network interface card on HP Debian Linux U1 Server?

Debian Linux provides GUI, command line tools and direct configuration file editing options to set up networking. Network configuration from the command line is possible.

Debian configure the network manually

You can use ip command or ifconfig command to configure IP address and other information on Debian Linux.

Task: Display the Current Network Configuration

Type the following command:
$ ip address show
Sample outputs:

1: lo:  mtu 16436 qdisc noqueue 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc pfifo_fast qlen 100
    link/ether 00:19:d1:2a:ba:a8 brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.1/24 brd 192.168.2.255 scope global eth0
    inet6 fe80::219:d1ff:fe2a:baa8/64 scope link 
       valid_lft forever preferred_lft forever
3: ra0:  mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:17:9a:0a:f6:44 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.106/24 brd 192.168.1.255 scope global ra0
    inet6 fe80::217:9aff:fe0a:f644/64 scope link 
       valid_lft forever preferred_lft forever
4: ppp0:  mtu 1496 qdisc pfifo_fast qlen 3
    link/ppp 
    inet 10.1.3.103 peer 10.0.31.18/32 scope global ppp0

You can also use ifconfig -a command, enter:
$ ifconfig -a
Sample outputs:

eth0      Link encap:Ethernet  HWaddr 00:19:D1:2A:BA:A8  
          inet addr:192.168.2.1  Bcast:192.168.2.255  Mask:255.255.255.0
          inet6 addr: fe80::219:d1ff:fe2a:baa8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:15819 errors:0 dropped:0 overruns:0 frame:0
          TX packets:27876 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:1695948 (1.6 MB)  TX bytes:40399983 (38.5 MB)
          Base address:0x1000 Memory:93180000-931a0000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:11943 errors:0 dropped:0 overruns:0 frame:0
          TX packets:11943 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:7024449 (6.6 MB)  TX bytes:7024449 (6.6 MB)

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:10.1.3.103  P-t-P:10.0.31.18  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1496  Metric:1
          RX packets:34922 errors:0 dropped:0 overruns:0 frame:0
          TX packets:15764 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3 
          RX bytes:50535608 (48.1 MB)  TX bytes:1256881 (1.1 MB)

ra0       Link encap:Ethernet  HWaddr 00:17:9A:0A:F6:44  
          inet addr:192.168.1.106  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::217:9aff:fe0a:f644/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:73809 errors:0 dropped:0 overruns:0 frame:0
          TX packets:31332 errors:1 dropped:1 overruns:0 carrier:0
          collisions:27 txqueuelen:1000 
          RX bytes:61373519 (58.5 MB)  TX bytes:5007190 (4.7 MB)
          Interrupt:20

The information is grouped by network interfaces. Every interface entry starts with a digit, called the interface index, with the interface name displayed after the interface index. In the above example, there are four interfaces:

  • lo : Loopback interface, used to access local services such as proxy or webserver http://127.0.0.1/
  • eth0 : The first Ethernet interface connected to network switch or router
  • ra0 : The first wireless interface
  • ppp0 :The first point-to-point interface, used to connect via VPN or dial up service

Task: Show Network Device / Interface Statistics

Type the following ip command
$ ip -s link show interface-name
$ ip -s link show eth0
$ ip -s link show ppp0
Sample outputs:

4: ppp0:  mtu 1496 qdisc pfifo_fast qlen 3
    link/ppp 
    RX: bytes  packets  errors  dropped overrun mcast   
    50537336   34946    0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    1257745    15776    0       0       0       0

Change the Current Network Configuration On Debian Linux

You must login as the root to change current network settings.

Task: Assign an IP Address to a Device Interface

In the following example, the command assigns the IP address 192.168.1.10 to the device eth0. The network mask is 24 (255.255.255.0) bits long. The brd + option sets the broadcast address automatically as determined by the network mask:
# ip address add 192.168.1.100/24 brd + dev eth0
You can also use ifconfig command, enter:
# ifconfig eth0 192.168.1.100 netmask 255.255.255.0 up

Task: Remove / Delete / Deactivate IP address from a device interface

To remove IP / delete device, enter:
# ip address del 192.168.1.100 dev eth0
OR
# ifconfig eth0 down

Save Network Settings to a Configuration File

To change the current network configuration setting you’ll need to edit/etc/network/interfaces[file] file using a text editor such as vi. This is the only way to save device setting to a configuration file so that system can remember changes after a reboot.

Task: Configure a Device Statically

Open [file]/etc/network/interfaces[/file file as the root user:
# vi /etc/network/interfaces
Let us assign static public routable (or private) IP address to eth0 interface, enter:
auto eth0
iface eth0 inet static
address 192.168.2.1
netmask 255.255.255.0
gateway 192.1.2.254

Save and close the file. Where,

  • auto eth0 : Identify the physical interfaces such as eth0, eth1 and so on
  • iface eth0 inet static : This method used to define ethernet interfaces with statically allocated IPv4 addresses
  • address 192.168.2.1 : Static IP address
  • netmask 255.255.255.0 : Static netmask
  • gateway 192.168.1.254 : Static gatway/router IP address

Task: Configure a Device Dynamically with DHCP

Open /etc/network/interfaces file as the root user:
# vi /etc/network/interfaces
Let us configure eth0 using DHCP. When the device is configured by using DHCP, you don’t need to set any options for the network address configuration in the file.
auto eth0
iface eth0 inet dhcp
Save and close the file.
Where,

  • auto eth0 : Identify the physical interfaces such as eth0, eth1 and so on
  • iface eth0 inet dhcp : This method used to define ethernet interfaces with DHCP server allocated IPv4 addresses

Start and Stop Configured Interfaces

To apply changes to a configuration file, you need to stop and restart the corresponding interface
# /etc/init.d/networking stop
# /etc/init.d/networking start
# /etc/init.d/networking restart
You can also use following command to bring down or up the eth0. Disables the device eth0, enter:
# ifdown eth0
Enables eth0 again, enter:
# ifup eth0

Defining the (DNS) Nameservers

Edit [file]/etc/resolv.conf, enter:
# vi /etc/resolv.conf
Update / add as follows:

### The IP addresses of nameservers ##
nameserver 8.8.8.8
nameserver 192.168.1.254

Save and close the file. Use dig command or host command to verify DNS connectivity:
$ host cyberciti.biz
dig cyberciti.biz

Further readings:

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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9 comment

  5. thanks. at last a doc worth looking at. have been trying for 3 days how to configure 2 nics on debian squeeze, most howto’s made no sense at all. had a quick read and less than 1 minute and everything is the way i wanted

    a tip if you are going to manually configure your network, for debian/ubunta at least. remove NetworkManager as it will overwrite everything you do:

    apt-get remove network-manager

    this gets rid of the gnome interface and whatever it does to manage network settings. once removed you can hack away

  6. I needed to make my IP static for the sake of machine shares, but I still wanted it to access the internet with this machine. For this /etc/networks/interfaces needed to be:

    auto eth0
    iface eth0 inet static
    address 192.168.0.5
    netmask 255.255.255.0
    gateway 192.168.0.1

    Using DHCP, the gateway address is populated. It needs to be added manually here. Good article though – it helped me out greatly!

  8. Note that in Debian Wheezy and I would assume later versions some (all?) net-tools commands are no longer available to mere mortals. Use of sudo or root seems to be required. Confused me when trying to tab complete if and nothing came up.

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