IP Addressing
The following section
describes the process of configuring your systems IP address and default
gateway needed for communicating on a local area network and the Internet.
Temporary IP Address
Assignment
For temporary network
configurations, you can use standard commands such as ip, ifconfig and route, which are also found on most other GNU/Linux operating systems.
These commands allow you to configure settings which take effect immediately,
however they are not persistent and will be lost after a reboot.
To temporarily configure
an IP address, you can use the ifconfig command in the following manner. Just modify the IP address and
subnet mask to match your network requirements.
sudo ifconfig eth0 10.0.0.100 netmask
255.255.255.0
To verify the IP address
configuration of eth0,
you can use the ifconfig command in the following manner.
ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:15:c5:4a:16:5a
inet addr:10.0.0.100 Bcast:10.0.0.255 Mask:255.255.255.0
inet6 addr:
fe80::215:c5ff:fe4a:165a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500
Metric:1
RX packets:466475604 errors:0
dropped:0 overruns:0 frame:0
TX packets:403172654 errors:0
dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2574778386 (2.5 GB) TX bytes:1618367329 (1.6 GB)
Interrupt:16
To configure a default
gateway, you can use the route command in the following manner. Modify the default gateway
address to match your network requirements.
sudo route add default gw 10.0.0.1 eth0
To verify your default
gateway configuration, you can use the route command in the following manner.
route -n
Kernel
IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 0.0.0.0 255.255.255.0 U
1 0 0 eth0
0.0.0.0 10.0.0.1 0.0.0.0 UG
0 0 0 eth0
If you require DNS for
your temporary network configuration, you can add DNS server IP addresses in
the file/etc/resolv.conf. The example below shows how to enter two DNS
servers to /etc/resolv.conf,
which should be changed to servers appropriate for your network. A more lengthy
description of DNS client configuration is in a following section.
nameserver
8.8.8.8
nameserver
8.8.4.4
If you no longer need
this configuration and wish to purge all IP configurations from an interface,
you can use the ip command with the flush option as shown below.
ip addr flush eth0
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Note:
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Flushing the IP configuration
using the ip command does not clear the contents of /etc/resolv.conf. You must remove or modify those entries manually.
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Dynamic IP Address
Assignment (DHCP Client)
To configure your server
to use DHCP for dynamic address assignment, add the dhcp method to the inet address family statement for
the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring
your first Ethernet interface identified as eth0.
auto
eth0
iface
eth0 inet dhcp
By adding an interface
configuration as shown above, you can manually enable the interface through the ifup command which initiates the DHCP process via dhclient.
sudo ifup eth0
To manually disable the
interface, you can use the ifdown command, which in turn will initiate the DHCP release process and
shut down the interface.
sudo ifdown eth0
Static IP Address
Assignment
To configure your system
to use a static IP address assignment, add the static method to the inet address family statement for
the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring
your first Ethernet interface identified as eth0. Change the address, netmask, and gateway values to meet the requirements of your network.
auto
eth0
iface
eth0 inet static
address
10.0.0.100
netmask
255.255.255.0
gateway
10.0.0.1
By adding an interface
configuration as shown above, you can manually enable the interface through the ifup command.
sudo ifup eth0
To manually disable the interface,
you can use the ifdown command.
sudo ifdown eth0
Loopback Interface
The loopback interface
is identified by the system as lo and
has a default IP address of 127.0.0.1. It can be viewed using the ifconfig
command.
ifconfig lo
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:2718 errors:0 dropped:0
overruns:0 frame:0
TX packets:2718 errors:0 dropped:0
overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:183308 (183.3 KB) TX bytes:183308 (183.3 KB)
By default, there should
be two lines in /etc/network/interfaces responsible for automatically configuring your loopback interface.
It is recommended that you keep the default settings unless you have a specific
purpose for changing them. An example of the two default lines are shown below.
auto
lo
iface
lo inet loopback
