All about ip command

ip - show / manipulate routing, devices, policy routing and tunnels

To show the NIC devices in the system

# ip link show
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
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:1c:c0:3e:4b:7e brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:19:5b:6b:53:22 brd ff:ff:ff:ff:ff:ff
4: venet0: <BROADCAST,POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
    link/void

This shows that there are 2 NIC cards - eth0 and eeth1 and both are UP.

To bring down an interface down

# ip link set eth0 down
 
# ip link show eth0
2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
    link/ether 00:1c:c0:3e:4b:7e brd ff:ff:ff:ff:ff:ff

To bring up the interface

# ip link set eth0 up

# ip link show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:1c:c0:3e:4b:7e brd ff:ff:ff:ff:ff:ff

To show the IP address

# ip addr show
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 00:1c:c0:3e:4b:7e brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.3/24 brd 192.168.1.255 scope global eth0
    inet6 fe80::21c:c0ff:fe3e:4b7e/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:19:5b:6b:53:22 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.7/24 brd 192.168.1.255 scope global eth1
    inet6 fe80::219:5bff:fe6b:5322/64 scope link
       valid_lft forever preferred_lft forever
4: venet0: <BROADCAST,POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
    link/void
    inet6 fe80::1/128 scope link
       valid_lft forever preferred_lft forever

# ip addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:1c:c0:3e:4b:7e brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.3/24 brd 192.168.1.255 scope global eth0
    inet6 fe80::21c:c0ff:fe3e:4b7e/64 scope link
       valid_lft forever preferred_lft forever