Checking your Network Connections on Linux
Connectivity in servers is fundamental and know how to manage it is really necessary. We can have network troubles at any time and this could impact our services, brand, and business. In this article, I will explain basic commands to manage our connectivity.
IP command
The ip command is very powerful and helpful when we need to manage our connections. Basically, the ip command is used to display and configure the network's parameters for server interfaces. IT has a simply syntaxis:
ip OPTIONS OBJECT COMMAND
Get information of all the networks interfaces
This command shows two interfaces in our server. The lo interface is a virtual network interface used by the server to communicate with itself. The ens33 is a second interface and it is used to connect to the internet or another network (the name could be different). We can see all information related to our connections as IP, broadcast, netmask, MAC address, etc.
[root@localhost ~]# ip a
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: wlp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 50:5b:c2:dd:de:89 brd ff:ff:ff:ff:ff:ff
inet 192.168.100.25/24 brd 192.168.100.255 scope global dynamic noprefixroute wlp1s0
valid_lft 259193sec preferred_lft 259193sec
inet6 2806:2f0:9020:4021:d3bc:10e6:ae0:52db/64 scope global dynamic noprefixroute
valid_lft 259196sec preferred_lft 172796sec
inet6 fe80::d8d3:785e:1332:8d86/64 scope link noprefixroute
valid_lft forever preferred_lft forever
NOTE: Command ip addr shows the same information as ip a
Obtaining detailed information of a single interface
We can obtain more information of an interface as stats of transmitted and received packets with the command ip -s link show {interface}
[root@localhost ~]# ip -s link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether 00:0c:29:9a:f2:b3 brd ff:ff:ff:ff:ff:ff
RX: bytes packets errors dropped overrun mcast
361033 1894 0 0 0 0
TX: bytes packets errors dropped carrier collsns
8033 67 0 0 0 0
The Route table
Another feature is the routing table. To obtain this informations, we need tu run the command: ip route show
[root@localhost ~]# ip route show
default via 192.168.100.1 dev ens37 proto dhcp metric 100
192.168.100.0/24 dev ens37 proto kernel scope link src 192.168.100.37 metric 100
Other important commands
Adding a new IP to a interface
The following command will add a new IP to an interface ip a add {ip_addr/mask} dev {interface}
[root@localhost ~]# ip a add 192.168.100.50/255.255.255.0 dev ens33
[root@localhost ~]# ip a
[...]
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:9a:f2:b3 brd ff:ff:ff:ff:ff:ff
inet 192.168.100.50/24 scope global ens33
valid_lft forever preferred_lft forever
[...]
As we can see, I added the IP address 192.168.100.20 to interface ens33.
Deleting an IP
The following command will delete an IP from an interface ip addr del {ip_addr/mask} dev {interface}
[root@localhost ~]# ip addr del 192.168.100.50/255.255.255.0 dev ens33
[root@localhost ~]# ip a
[...]
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:9a:f2:b3 brd ff:ff:ff:ff:ff:ff
[...]
After running the command, the IP address 192.168.100.50 was deleted from the ens33 interface.
How to enable/disable a network interface
In case that you want to disable or enable a network interface, you can do it using a simple command. If you run the command ip a, in the properties of the interface, there is a state parameter, which indicates the state enable or disable (UP/DOWN) for the interface.
How to enable network interface
The following command will enable a network interface ip link set {interface} up
[root@localhost ~]# ip link set ens33 up
...
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:9a:f2:b3 brd ff:ff:ff:ff:ff:ff
...
How to disable network interface
The following command will disable a network interface ip link set {interface} down
[root@localhost ~]# ip link set ens33 down
...
2: ens33: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
link/ether 00:0c:29:9a:f2:b3 brd ff:ff:ff:ff:ff:ff
...
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Updated 12 months ago