Working with Network on CentOS/RHEL 07 - Part 12

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Configure DHCP IP address using configuration files

- We will simply see a basic example of changing IP address to DHCP mode using “ifcfg-*” files present in network-script directory of NetworkManager Daemon service.

- First check for the existing content in the configuration file

[root@myserver2 network-scripts]# cat ifcfg-Wired_connection_3

TYPE=Ethernet

BOOTPROTO=none

DEFROUTE=yes

IPV4_FAILURE_FATAL=no

IPV6INIT=no

NAME=Wired_connection_3

UUID=46a40de1-e50a-4b1f-90e4-413cc53a34e9

DEVICE=enp0s9

ONBOOT=yes

HWADDR=08:00:27:B6:50:F3

IPADDR=192.168.248.100

PREFIX=24

[root@myserver2 network-scripts]# ip a sh dev enp0s9

4: enp0s9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

    link/ether 08:00:27:b6:50:f3 brd ff:ff:ff:ff:ff:ff

    inet 192.168.248.100/24 brd 192.168.248.255 scope global enp0s9

       valid_lft forever preferred_lft forever

    inet6 fe80::a00:27ff:feb6:50f3/64 scope link

       valid_lft forever preferred_lft forever

- Now time to get some changes done to the configuration file, in our example we will change the IP address so new IP

[root@myserver2 network-scripts]# vi ifcfg-Wired_connection_3

[root@myserver2 network-scripts]# cat ifcfg-Wired_connection_3

TYPE=Ethernet

BOOTPROTO=dhcp

DEFROUTE=yes

IPV4_FAILURE_FATAL=no

IPV6INIT=no

NAME=Wired_connection_3

UUID=46a40de1-e50a-4b1f-90e4-413cc53a34e9

DEVICE=enp0s9

ONBOOT=yes

HWADDR=08:00:27:B6:50:F3

#IPADDR=192.168.248.100

#PREFIX=24

- Post changes in the configuration file, to get those reflected get the interface down and up using ifdown and ifup commands.

[root@myserver2 network-scripts]# ifdown enp0s9

[root@myserver2 network-scripts]# nmcli dev status

DEVICE   TYPE      STATE         CONNECTION

enp0s3   ethernet  connected     Wired_connection_1

enp0s8   ethernet  connected     Wired_connection_2

enp0s10  ethernet  disconnected  --

enp0s9   ethernet  disconnected  --

lo       loopback  unmanaged     --

[root@myserver2 network-scripts]# ifup enp0s9

Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/7)

[root@myserver2 network-scripts]# nmcli dev status

DEVICE   TYPE      STATE         CONNECTION

enp0s3   ethernet  connected     Wired_connection_1

enp0s8   ethernet  connected     Wired_connection_2

enp0s9   ethernet  connected     Wired_connection_3

enp0s10  ethernet  disconnected  --

lo       loopback  unmanaged     --

[root@myserver2 network-scripts]# ip a sh dev enp0s9

4: enp0s9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

    link/ether 08:00:27:b6:50:f3 brd ff:ff:ff:ff:ff:ff

    inet 192.168.248.203/24 brd 192.168.248.255 scope global dynamic enp0s9

       valid_lft 1174sec preferred_lft 1174sec

    inet6 fe80::a00:27ff:feb6:50f3/64 scope link

       valid_lft forever preferred_lft forever

- Permanent changes has been made successfully to the interface using configuration files.

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