Network is included by two or more computers that are linked to share resources (such as printers and CDs), exchange files, or allow electronic communications. NetworkManager is the configuration of the network on the interfaces, which is the software utility that aims to simplify the use of computer networks.
Check the connection
To ensurethe network connection, go through the following conditions below:
network interfaceis listed and enabled. Otherwise, check the device driver.
- Making sure that you are connected with a network cable or connected to the
- Your network interface has an
- You can
pinga local IP Address (e.g.
The default gateway.)
- You can also
pinga public IP Address(e.g.
The google DNS server).
Reset Network Manager Service
This is the easiest way to restart your network using the command line. It’s equivalent to the graphical way of doing it (restarts the Network-Manager service).
sudo service network-manager restart
The network icon should disappear for a moment and then reappear.
Reset System of Network Manager
The service command is just a wrapper for this method (and also for init.d scripts and Upstart commands). The
systemctl command is much more versatile than service. This is what I usually prefer.
sudo systemctl restart NetworkManager.service
The network icon (again) should disappear for a moment. To check out other
systemctl options, you can refer to its man page.
Turn OFF and ON Network Manager
This is yet another tool for handling networks. It is a pretty powerful tool that you can find it very practical. Many sysadmins prefer it since it is easy to use.
There are two steps to this method: turning the network off, and then turning it back on.
sudo nmcli networking off sudo nmcli networking on
You can check out the man page of nmcli for more options.
Ping has been used as the command for testing if you have reached to a host or not.
Down here is the example:
[email protected]$~ ping www.google.com PING www.google.com (22.214.171.124) 56(84) bytes of data. 64 bytes from 126.96.36.199: icmp_seq=1 ttl=109 time=32.3 ms 64 bytes from 188.8.131.52: icmp_seq=2 ttl=109 time=33.6 ms 64 bytes from 184.108.40.206: icmp_seq=3 ttl=109 time=33.5 ms
If you receive an error like
pingL icmp open socket: Operation not permitted when executing
ping, try to re-install iputils package.
An Internet Protocol Address (IP Address) is a numerical label assigned to each device connected to a
computer network that uses the
internet protocol for communication.
An IP address serves two main functions:
- The host or Network interface
- The location
version 4 (IPv4) defines an IP address as a
To discover which IP addresses your computer has, you use the
ip command with the object
address.The default action is
show, which lists the IP addresses. You can also omit
show and abbreviate
address as “addr” or even “a”.
The following commands are all equivalent:
ip address show
ip addr show
The output is down below:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qle link/ether 34:41:5d:83:dd:fd brd ff:ff:ff:ff:ff:ff inet 192.168.10.107/24 brd 192.168.10.255 scope global dynamic noprefixroute wlan0 valid_lft 5938sec preferred_lft 5938sec inet6 fe80::ba0c:6781:2174:12f4/64 scope link noprefixroute valid_lft forever preferred_lft forever
We can see two IP addresses, along with a lot of other information. The IP addresses are associated with the network interface controller(NICs). The
ip command tries to be helpful and provides a bunch of information about the interface, too.
The first IP address is the (internal) loopback address used to communicate within the computer. The second is the actual (external) IP address the computer has on the local area network (LAN).
Let’s break down all the information we received:
lo: The network interface name as a string.
<LOOPBACK,UP,LOWER_UP>: This is a loopback interface. It is
UP, meaning it’s operation. The Physical networking layer(layer one) is also up.
mtu 65536: The maximum transfer unit. This is the size of the largest chunk of data this interface can transmit.
qdisc noqueue: A
qdiscis a queuing mechanism. It schedules the transmission of packets. There are different queuing techniques called disciplines. The
noqueuediscipline means “send instantly, don’t queue.” This is the default
qdiscdiscipline for virtual devices, such as the loopback address.
state UNKNOWN: This can be
DOWN(the network interface is not operational),
UNKNOWN(the network interface is operational but nothing is connected), or
UP(the network is operational and there is a connection).
group default: Interfaces can be grouped logically. The default is to place them all in a group called “default.”
qlen 1000: The maximum length of the transmission queue.
link/loopback: The media access control (MAC) address of the interface.
inet 127.0.0.1/8: The IP version 4 address. The part of the address after the forward-slash (/) is Classless Inter-Domain Routing notation (CIDR) representing the subnet mask. It indicates how many leading contiguous bits are set to one in the subnet mask. The value of eight means eight bits. Eight bits set to one represents 255 in binary, so the subnet mask is 255.0.0.0.
scope host: The IP address scope. This IP address is only valid inside the computer (the “host”).
lo: The interface with which this IP address is associated.
valid_lft: Valid lifetime. For an IP version 4 IP address allocated by Dynamic Host Configuration Protocol (DHCP), this is the length of time the IP address is considered valid and able to make and accept connection requests.
preferred_lft: Preferred lifetime. For an IP version 4 IP address allocated by
DHCP, this is the amount of time the IP address can be used with no restrictions. This should never be larger than the
<BROADCAST,MULTICAST,UP,LOWER_UP>: This interface supports
multicasting, and the interface is UP (operational and connected). The hardware layer of the network (layer one) is also UP.
Display Only IPv4 and IPv6 Addresses
If you want to limit the output to the IP version 4 addresses, you can use the
-4 option, as follows:
ip -4 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever 2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 inet 192.168.10.107/24 brd 192.168.10.255 scope global dynamic noprefixroute wlan0 valid_lft 4487sec preferred_lft 4487sec
if you want to limit the output to the IP version 6 addresses, you can use the
-6 option, as follows:
ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000 inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000 inet6 fe80::ba0c:6781:2174:12f4/64 scope link noprefixroute valid_lft forever preferred_lft forever
Display Information for Single Interface
If you want to see the IP address information for a single interface, you can use the
dev options, and name the interface, as shown below.
ip addr show dev <Network_Interface_Name>
ip addr show dev lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever
You can also use the -4 or -6 flag to further refine the output so you only see that in which you’re interested.
Sample: If you want to see the IP version 4 information related to addresses on interface
lo, type the following command.
ip -4 addr show dev lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever
Adding an IP Address
You can use the
dev options to add an IP address to an interface. You just have to tell the
ip command which IP address to add, and to which interface to add it.
We’re going to add the IP address 192.168.4.44 to the
lo interface. We also have to provide the CIDR notation for the subnet mask.
We type the following:
sudo ip addr add 192.168.4.44/24 dev lo
The new IP Address is present on the network interface.
We can jump on another computer and use the following command to see if we can
ping the new IP address.
[email protected]$~ ping 192.168.4.44 PING 192.168.4.44 (192.168.4.44) 56(84) bytes of data. 64 bytes from 192.168.4.44: icmp_seq=1 ttl=64 time=0.039 ms 64 bytes from 192.168.4.44: icmp_seq=2 ttl=64 time=0.092 ms 64 bytes from 192.168.4.44: icmp_seq=3 ttl=64 time=0.109 ms
The IP address responds and sends back acknowledgments to the pings. Our new IP address is up and running after one simple
Deleting IP Address
To delete an IP address, the command is almost the same as the one to add one, except you replace
del, as shown below:
sudo ip addr del 192.168.4.44/24 dev lo
Using IP With Network Interfaces
You use the
link object to inspect and work with network interfaces. Type the following command to see the interfaces installed on your computer:
ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DORMANT group default qlen 1000 link/ether 34:41:5d:83:dd:fd brd ff:ff:ff:ff:ff:ff
To see a single network interface, just add its name to the command, as shown below:
ip link show <Network_Interface_Name>
ip link show lo
Starting and Stopping Links
You can use the
set options with either
down to stop or start network interface option. You can also have to use sudo (Super User), as shown below.
sudo ip link set <Network_Interface_Name> <up or down>
sudo ip link set lo down
If you use the
up option, your network interface will be restarted, and the state is shown as
Usinng IP With Routes
With the route object, you can inspect and manipulate routes. Routes define to where network traffic to different IP addresses is forwarded, and through which network interface.
If the destination computer or device shares a network with the sending computer, the sending computer can forward the packet directly to it.
However, if the destination device is not directly connected, the sending computer forwards the packet to the default router. The router then decides where to send the packet.
To see the routes defined on your computer, type the following command:
default via 192.168.10.1 dev wlan0 proto dhcp metric 600 192.168.10.0/24 dev wlan0 proto kernel scope link src 192.168.10.107 metric 600
Let’s take a look at the info we received:
- default: The default rule. This route is used if none of the other rules match what’s being sent.
- via 192.168.10.1: Routes the packets via the device at 192.168.10.1. This is the IP address of the default router on this network.
- dev wlan0: Use this network interface to send the packets to the router.
- proto dhcp: The routing protocol identifier. DHCP means the routes will be determined dynamically.
- metric 100: An indication of the preference of the route compared to others. Routes with lower metrics are preferentially used over those with higher metrics. You can use this to give preference to a wired network interface over a Wi-Fi one.
Display Information for Single Route
If you want to focus on the details of a particular route, you can add the
list option and IP address range of the route to the command as follows:
ip route list <ip_address>
We just added a new network interface card to this computer. We type the following and it’s showing up as
We’ll add a new route to the computer to use this new interface. First, we type the following to associate an IP address with the interface:
sudo ip addr add 192.168.121.1/24 dev wlan2
A default route using the existing IP address is added to the new interface. We use the
delete option, as shown below, to delete the route and provide its details:
sudo ip route delete default via 192.168.4.1 dev wlan2
We’ll now use the add option to add our new route. The new interface will handle network traffic in the 192.168.121.0/24 IP address range. We’ll give it a metric of 100; because it will be the only route handling this traffic, the metric is pretty much academic.
We type the following:
sudo ip route add 192.168.121.0/24 dev wlan2 metric 100
Now , typing
ip route command to see what it gives. As our new route is now in place;however, we still have the 192.168.4.0/24 route that points to interface enp0s8—we type the following to remove it:
sudo ip route delete 192.168.4.0/24 dev wlan2
We should now have a new route that points all traffic destined for IP range 192.168.121.0/24 through interface
wlan2. It should also be the only route that uses our new interface.
Taken Route, Not Taken Root
The great thing about these commands is they’re not permanent. If you want to clear them, just reboot your system. This means you can experiment with them until they work the way you want. And it’s a very good thing if you make a terrible mess of your system—a simple reboot will restore order.
On the other hand, if you want the changes to be permanent, you have to do some more work. Exactly what varies depending on the distribution family, but they all involve changing config files.
This way, though, you can test-drive commands before you make anything permanent.