Linux: How To Configure Network

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When running a linux machine, it is beneficial to have a basic understanding of networking tools for configuring or inspecting various settings. This post will go through several linux utilities for configuring network equipment.

Network Interfaces

It is the connection between a computer and a network. To put it simply, it links up the network side of the software to the hardware side. There are basically two types of network interfaces in a linux system: physical interfaces and virtual interfaces. A network hardware device, such as a modem, NIC (Network Interface Card), or WNIC (Wireless Network Interface Card), is represented by a physical network interface. On the other hand, a virtual interface is linked to network devices, not to a hardware device. 

Let’s check the network interfaces available on your system by running the command below.

$ ls /sys/class/net

G4 MQVO9qrZOL0PGMq2caziF yATTcXqrs - Linux: How To Configure Network

In my system, there are two network interfaces available and they are lo and wlo1. The lo (loopback interface) is a special interface that is used by the system to communicate with itself. And the wlo1 is a wireless network interface (NIC). To view more information about these interfaces run the command below.

$ ifconfig -a

E0itrPknRWi3ZS KLcz0obH3uh4b4f1ImcmplAGDaxhNep7AxDSYPE pPdOoz7AWQHcGp1P pxc9ZbRyufEsQB X9wizU7ld2sWOmKLfWmooXlC9yn6ASOu2Y1aXTT2TQfAJ7kgK en7 2b4eRZs66VDu0vjO ZrkpuX2gJf0PBRXsenz6LDSoGfTg - Linux: How To Configure Network

A great chunk of information is shown in the terminal which is discussed below.

  • UP/DOWN: Interfaces can be in two modes UP or DOWN. If you want to turn off an interface, you have to down the interface.
  • BROADCAST: Refers to the point that the network is configured to handle broadcast packets which is vital to get the IP address.
  • RUNNING: This means that the network is ready to accept data. 
  • mtu: stands for maximum transmission unit. If IP datagrams are larger than MTU bytes, they will be divided into multiple Ethernet frames. 
  • inet: it is the IPv4 IP address of the interface.  
  • inet6: it is the IPv6 IP address of the interface.  
  • MULTICAST: it refers to an interface supporting multicasting.
  • RX packets: number of the received data packets by the interface. 
  • RX errors: shows the total number of packets received with an error. 
  • RX dropped: Several packets are dropped as a result of unwanted VLAN tagging or receiving IPv6 frames on an interface that isn’t set up for IPv6.
  • RX overruns: Several received packets encountered FIFO overruns as a result of the speed at which a buffer fills up and the kernel’s inability to clear it.

For transmission (TX), TX packets, TX errors, TX dropped, and TX overruns represent similar things as RX.    

To turn up or turn down an interface,

$ ifup [interface name]
$ ifdown [interface name]

If these commands are not found on your system, you have installed the ifupdown package which can be done using the following command.

$ sudo apt install ifupdown

You can also achieve this stuff using the ip command. Some basic commands are listed below. To view the available interfaces,

$ ip link

Xmcqf8zKSN SS4C33sVlpMCA4Qbrd9TXP5gphUgCwmebofdSJ4X M1qbGs1XHM1b0yJxVEaDxO5hytDQTSRzHQGQD9DuTi402RYBg6 gUggB6IYJJdcOyfsvWwFWJ7shbDpx6UcI P Q1m2A5vbjpc7Mrxr5kY1GJoZmnSOEE5zAYd0sVsD tmQQ - Linux: How To Configure Network

To view the IP addresses of the interface,

UpO9LoIpwkIbkQpueGl0VbjLc43nkFwX6F2tTw59joSqFqb99duFfkslGmgiWE2uEQFaE j9Xr8tbfOX0xfoS AeqUU73TEfumQdptO 4ryc FP1BaynGS5hSsJcu0GnoakEzIQ ZYZHdMnZCGk3Swzhfc4S8lzP8ZfSNQDAuuRgQJ2gDQN rjiZTw - Linux: How To Configure Network

To turn on or off an interface,

$ ip link set [interface name] up
$ ip link set [interface name] down

Network Manager

It configures your network automatically. It would be extremely inconvenient for users if they had to set up the system every time they booted it. It is in charge of the network hardware. After starting, the system looks for and activates any accessible wired or wireless network for hardware. There is an excellent tool named nmclient. Run it in the terminal.

$ nmclient
wlo1: connected to Sabre_5G
        "Realtek RTL8821CE"
        wifi (rtw_8821ce), DC:F5:05:DB:3F:2F, hw, mtu 1500
        ip4 default
        inet6 fe80::94a8:1899:827e:60c/64
        route6 fe80::/64

lo: unmanaged
        loopback (unknown), 00:00:00:00:00:00, sw, mtu 65536

DNS configuration:
        interface: wlo1

Use "nmcli device show" to get complete information about known devices and
"nmcli connection show" to get an overview on active connection profiles.

Consult nmcli(1) and nmcli-examples(7) manual pages for complete usage details.

Find MAC Address

In computer networking, ARP stands for address resolution protocol. The main goal of the ARP is to find out the MAC address of a device associated with a specific IP address. There is a tool in linux named arp which performs the job for us.  Just run the command.

$ arp -n

WvT2gIVCwiub3tGQyzl90Ejh lvME3Ff iW embz P3 5VMCPS pG38OyOEZ99u2NIBD65uFoS1M452 VBWaFo0RlKMQqNGVQKkp 8PX vOokH0hrhePrIw - Linux: How To Configure Network

When you run the command, it looks in the ARP cache. HWaddress is a MAC address associated with the IP address. There are options that be passed with the command. Some basic options are listed below.

  • -n: it shows the numeric format of the addresses instead of names or symbols
  • -v: shows the verbose information. 
  • -d: it deletes the specified MAC address from the arp cache. Be careful in terms of running this command. You may delete your primary network connection. In that case, you have to reboot the system. 

There is another tool for this action named ip neigh which shows the information similar to the arp command. The reason for using ip neigh is that the arp command is now close to depreciation and many of the dependencies of arp are now obsolete. But arp command still maintains its popularity. Let’s run the ip neigh command below and check its output.

$ ip neigh

0jp ggVsFOSm QmCUq36LIDIAzXvJ7svCUqcjYN5TFbj1vSvT6GZmZBgWlrd6t0GMMdaZyVejP7hjV1N4wOp - Linux: How To Configure Network

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