Many of the core Fedora / Redhat commands and configuration files covered in this chapter can be used in Debian based operating systems, but there are some key differences.
The /etc/network/interfaces File
The main network configuration file is the /etc/network/interfaces file in which all the network interface parameters are defined. The file is divided into stanzas:
The auto Stanza
The auto stanza defines the interfaces that should be automatically initialized when the system boots up.
The mapping Stanza
This stanza maps configuration parameters for an interface depending on the output of a script. For example, on booting the script could prompt you as to whether your laptop Linux system is at home or work with the mapping statement using the answer to configure the appropriate IP address.
By default the much simpler hotplug system is used which assumes that the interfaces will have only one purpose. Typical hotplug configurations simply assign each physical interface with a matching logical interface name (nick name).
mapping hotplug script grep map eth0 eth0 map eth1
In this case interface eth0 is specifically given the logical name eth0, while the logical name for eth1 is implied to be the same.
The iface Stanza
The iface stanza defines the characteristics of a logical interface. Typically the first line of these stanzas starts with the word iface, followed by the logical name of the interface, the protocol used, and finally the type of addressing scheme to be used, such as DHCP or static. Protocol keywords include inet for regular TCP/IP, inet6 for IPv6, ipx for the older IPX protocol used by Novell, and loopback for loopback addresses.
Subsequent lines in the stanza define protocol characteristics such as addresses, subnet masks, and default gateways. In this example, interface eth1 is given the IP address 188.8.131.52/27 while interface eth0 gets its IP address using DHCP.
# The primary network interface auto eth1 iface eth1 inet static address 184.108.40.206 netmask 255.255.255.224 network 220.127.116.11 broadcast 18.104.22.168 gateway 22.214.171.124 dns-nameservers 126.96.36.199 # The secondary network interface auto eth0 iface eth0 inet dhcp
Note: When static IP addresses are used, a default gateway usually needs to be defined. Remember to place the gateway statement in the correct stanza with the appropriate router IP address.
Creating Interface Aliases
IP aliases can be easily created in the /etc/network/interfaces file once the main interface has already been defined. A modified duplicate of the main interfaces’ iface stanza is required. A colon followed by the sub interface number needs to be added to the first line, and only the subnet mask and the new IP address needs to follow as can be seen in this example for interface eth1:1 with the IP address 188.8.131.52.
auto eth1:1 iface eth1:1 inet static address 184.108.40.206 netmask 255.255.255.224
Adding Permanent Static Routes
up option in the appropriate
iface stanza of the
/etc/network/interfaces file allows you to selectively run commands once the specified interface becomes activated with the
ifup command. This makes it useful when adding permanent static routes.
In this example, a route to the 10.0.0.0/8 network via router address 220.127.116.11 has been added. Remember, the
up option and the command must reside on the same line of the stanza.
# The primary network interface auto eth1 iface eth1 inet static ... ... ... up route add -net 10.0.0.0 netmask 255.0.0.0 gw 18.104.22.168 eth1
A complete /etc/network/interfaces file
We can now construct a complete file based on the previous examples we discussed. Just like in Fedora, interfaces can be activated with the ifup and ifdown commands.
# # Debian / Ubuntu # # # File: /etc/network/interfaces # # The loopback network interface auto lo iface lo inet loopback # This is a list of hotpluggable network interfaces. # They will be activated automatically by the hotplug subsystem. mapping hotplug script grep map eth0 eth0 map eth1 eth1 # The primary network interface auto eth1 iface eth1 inet static address 22.214.171.124 netmask 255.255.255.224 network 126.96.36.199 broadcast 188.8.131.52 gateway 184.108.40.206 # dns-* options are implemented by the resolvconf package, if installed dns-nameservers 220.127.116.11 wireless-key 98d126d5ac wireless-essid schaaffe up route add -net 10.0.0.0 netmask 255.0.0.0 gw 18.104.22.168 eth1 auto eth1:1 iface eth1:1 inet static address 22.214.171.124 netmask 255.255.255.224 # The secondary network interface auto eth0 iface eth0 inet dhcp
For more information on the
/etc/network/interfaces file just issue the command
man interfaces from the command line.