Configuring network interfaces from command line is all well, but now it is time to learn how to tell vm1 to configure them automatically. For this you will learn about the /etc/network/interfaces configuration file:

user1@vm1:~$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
 
# The loopback network interface
#(1) (2)
auto lo
#(3)   (4)(5)  (6)
iface lo inet loopback
 
# The primary network interface
#(7)           (8)
allow-hotplug eth0
#(9)   (10) (11) (12)
iface eth0 inet dhcp

As usual, fields and their descriptions:

Other important files which contain network configuration, but we will not touch them for here:

1. /etc/hosts — a computer file used in an operating system to map hostnames to IP addresses. The hosts file is a plain text file and is conventionally named hosts.
2. /etc/hostname — a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication.
3. /etc/resolv.conf — a computer file used in various operating systems to configure the Domain Name System (DNS) resolver library. The file is a plain-text file usually created by the network administrator or by applications that manage the configuration tasks of the system. The resolvconf program is one such program on linux machines which manages the resolv.conf file.

Let us remember tap0 from previous exercise. If you reboot vm1 it is gone. Of course you can enable it by retyping relevant commands, but let us imagine that you need it to become available automatically after reboot.

Now you will learn how to configure an interface using /etc/network/interfaces file.

1: ip a s
2: sudo vim /etc/network/interfaces

Now add this lines to the end of configuration file:

 3: auto tap0
 4: iface tap0 inet static
 5:         address 10.2.2.2
 6:         netmask 255.255.255.0
 7:         tunctl_user uml-net
 8:
 9: allow-hotplug tap1
10: iface tap1 inet static
11:         address 10.3.3.3
12:         netmask 255.255.255.0

Now type :wq<ENTER> and continue:

13: sudo /etc/init.d/networking start
14: ip a s
15: sudo tunctl -t tap1 -u uml-net
16: ip a s

user1@vm1:~$ ip a s
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    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: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:d4:45:68 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
    inet6 fe80::a00:27ff:fed4:4568/64 scope link
       valid_lft forever preferred_lft forever
user1@vm1:~$ sudo vim /etc/network/interfaces
# and how to activate them. For more information, see interfaces(5).
 
# The loopback network interface
auto lo
iface lo inet loopback
 
# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp
 
auto tap0
iface tap0 inet static
        address 10.2.2.2
        netmask 255.255.255.0
        tunctl_user uml-net
 
allow-hotplug tap1
iface tap1 inet static
        address 10.3.3.3
        netmask 255.255.255.0
~
"/etc/network/interfaces" 21L, 457C written               21,1-8        Bot
user1@vm1:~$ sudo /etc/init.d/networking start
Configuring network interfaces...Set 'tap0' persistent and owned by uid 104 done.
user1@vm1:~$ ip a s
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    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: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:d4:45:68 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
    inet6 fe80::a00:27ff:fed4:4568/64 scope link
       valid_lft forever preferred_lft forever
3: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500
    link/ether 46:63:30:70:b5:21 brd ff:ff:ff:ff:ff:ff
    inet 10.2.2.2/24 brd 10.2.2.255 scope global tap0
    inet6 fe80::4463:30ff:fe70:b521/64 scope link
       valid_lft forever preferred_lft forever
user1@vm1:~$ sudo tunctl -t tap1 -u uml-net
Set 'tap1' persistent and owned by uid 104
user1@vm1:~$ ip a s
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    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: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:d4:45:68 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
    inet6 fe80::a00:27ff:fed4:4568/64 scope link
       valid_lft forever preferred_lft forever
3: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500
    link/ether 46:63:30:70:b5:21 brd ff:ff:ff:ff:ff:ff
    inet 10.2.2.2/24 brd 10.2.2.255 scope global tap0
    inet6 fe80::4463:30ff:fe70:b521/64 scope link
       valid_lft forever preferred_lft forever
4: tap1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500
    link/ether 8a:ed:90:33:93:55 brd ff:ff:ff:ff:ff:ff
    inet 10.3.3.3/24 brd 10.3.3.255 scope global tap1
    inet6 fe80::88ed:90ff:fe33:9355/64 scope link
       valid_lft forever preferred_lft forever
user1@vm1:~$

1. Print out current interface configuration.
2. Edit /etc/network/interfaces.
3. Automatically configure tap0.
4. Set the following IPv4 static parameters fop tap0.
5. Add IP address 10.2.2.2 to tap0.
6. Specify netmask for this IP address. Parameters broadcast and network are derived from this netmask automatically.
7. Specify user who will own tap0 interface.
8. Empty line for readability.
9. Add the following parameters to tap1 interface when it appears in the system.
10. Set the following IPv4 static parameters fop tap1.
11. Add IP address 10.3.3.3 to tap0.
12. Specify netmask for this IP address.
13. Applies changes in network configuration.
14. Prints out current interface configuration. You are able to see that tap0 is add to the list of interfaces.
15. Adds tap1 pseudo-interface.
16. Prints out current interface configuration. You are able to see that its parameters specified in /etc/network/interfaces are applied to it automatically.

1. Explain how network and broadcast parameters are derived.
2. Try this: ping kitty. Failure is expected. Now add an entry to /etc/hosts so that you will be able to successfully ping.