Ip

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In newer versions of Operating Systems such as Fedora 20 or CentOS 7, older ifconfig and route commands are discontinuted. In such operating systems the only option is to use 'ip' command for obtaining network information.

Obtaining current configuration

To look at current IP address configuration use:

ip addr show

Similarly to look at current routes use:

ip route show

Persistent IP address configuration

To configure a static IP on an interface use following steps:

1. Created or edit '/etc/sysconfig/network-scripts/ifcfg-<interface>' file. For example for eth0 it would be /etc/sysconfig/network-scripts/ifcfg-eth0
2. In file configure persistent IP address (DHCP or static) as follows:

   DEVICE=eth0
   BOOTPROTO=static
   IPADDR="10.0.0.2"
   NETMASK="255.255.255.0"
   GATEWAY="10.0.0.1"
   DNS1="4.2.2.2"
   DNS2="8.8.8.8"
   ONBOOT="yes"
   NM_CONTROLLED="no"
   HWADDR=<MAC-address>

3. Then use command "systemctl restart network" to restart network service and new configuration to take effect
4. Then use "ip addr show" to list current IP addresses in use

Persistent static route configuration

To configure persistent static routes use following steps:

1. Created or edit '/etc/sysconfig/network-scripts/route-<interface>' file. For example for eth0 it would be /etc/sysconfig/network-scripts/route-eth0
2. In file configure persistent static route as follows:

   10.10.1.0/24 via 10.0.0.3 dev eth0

3. Then use command "systemctl restart network" to restart network service and new configuration to take effect
4. Then use "ip route show" to list current routes in use

IP configuration commands

To configure IP address using commands, where the changes would be lost on machine reboot, use:

ip addr add 10.0.0.2 dev eth0

To configure static routes for current session (till next shutdown or reboot) use:

ip route add 10.10.1.0/24 via 10.0.0.3 dev eth0

To configure default route use

ip route add default via 10.0.0.1

Note that IP addresses can be removed using:

ip addr del 10.0.0.2 dev eth0

Similarly routes can be removed using

ip route del 10.10.1.0/24 via 10.0.0.3 dev eth0

To change interface state to up

To make interface up without assigning IP adddress (for capturing packets, etc.) use:

ip link set eth0 up

Similalry to make interface down without removing IP address use:

ip link set eth0 down

Note that down interfaces do not communicate with external network. But access to IP assigned to a local interface even if it is down will work.

To change interface MTU

To change interface MTU use:

ip link set eth0 mtu 1400

Steps learned from http://www.tecmint.com/ip-command-examples/

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