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Networking configuration

Prerequisites

  • A certain amount of comfort operating from the command line
  • Elevated or administrative privileges on the system (For example root, sudo and so on)
  • Optional: familiarity with networking concepts

Introduction

Nowadays a computer without network connectivity is almost useless by itself. Whether you need to update the packages on a server or simply browse external Websites from your laptop - you will need network access!

This guide aims to provide Rocky Linux users the basic knowledge on how to setup network connectivity on a Rocky Linux system.

Using NetworkManager service

At the user level, the networking stack is managed by NetworkManager. This tool runs as a service, and you can check its state with the following command:

systemctl status NetworkManager

Configuration files

NetworkManager simply applies a configuration read from the files found in /etc/sysconfig/network-scripts/ifcfg-<IFACE_NAME>. Each network interface has its configuration file. The following example in the default configuration for a server:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
NAME=ens18
UUID=74c5ccee-c1f4-4f45-883f-fc4f765a8477
DEVICE=ens18
ONBOOT=yes
IPADDR=192.168.0.1
PREFIX=24
GATEWAY=192.168.0.254
DNS1=192.168.0.254
DNS2=1.1.1.1
IPV6_DISABLED=yes

The interface's name is ens18 so this file's name will be /etc/sysconfig/network-scripts/ifcfg-ens18.

Tips:
There are a few ways or mechanisms by which systems can be assigned their IP configuration information. The 2 most common methods are - Static IP configuration scheme and Dynamic IP configuration scheme.

The static IP configuration scheme is very popular on server class systems or networks.

The dynamic IP approach is popular on home and office networks - or workstation and desktop class systems. The dynamic scheme usually needs something extra that is locally available that can supply proper IP configuration information to requesting workstations and desktops. This something is called the Dynamic Host Configuration Protocol (DHCP).

Very often, home/office users don't have to worry or know about DHCP. This is because the somebody or something else is automagically taking care of that in the background. The only thing that the end user needs to do is to physically or wirelessly connect to the right network (and of course make sure that their systems are powered on)!

IP Address

In the previous /etc/sysconfig/network-scripts/ifcfg-ens18 listing, we see that the value of the BOOTPROTO parameter or key is set to none. This means that the system being configured is set to a static IP address scheme.

If instead you want to configure the system to use a dynamic IP address scheme, you will have to change the value of the BOOTPROTO parameter from none to dhcp and also remove the IPADDR, PREFIX and GATEWAY lines. This is necessary because all of that information will be automaically obtained from any available DHCP server.

To configure a static IP address attribution, set the following:

  • IPADDR: the IP address to assign the interface
  • PREFIX: the subnet mask in CIDR notation
  • GATEWAY: the default gateway

The ONBOOT parameter set to yes indicates that this connection will be activated during boot time.

DNS resolution

To get proper name resolution, the following parameters must be set:

  • DNS1: IP address of the main nameserver
  • DNS2: the secondary nameserver IP address

Apply configuration

To apply the network configuration, the nmcli command can be used:

nmcli connection up ens18

To get the connection state, simply use:

nmcli connection show

You can also use the ifup and ifdown commands to bring the interface up and down (they are simple wrappers around nmcli):

ifup ens18
ifdown ens18

Checking configuration

You can check that the configuration has been correctly applied with the following nmcli command:

nmcli device show ens18

which should give you the following output:

GENERAL.DEVICE:                         ens18
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         6E:86:C0:4E:15:DB
GENERAL.MTU:                            1500
GENERAL.STATE:                          100 (connecté)
GENERAL.CONNECTION:                     ens18
GENERAL.CON-PATH:                       /org/freedesktop/NetworkManager/ActiveConnection/1
WIRED-PROPERTIES.CARRIER:               marche
IP4.ADDRESS[1]:                         192.168.0.1/24
IP4.GATEWAY:                            192.168.0.254
IP4.ROUTE[1]:                           dst = 192.168.0.0/24, nh = 0.0.0.0, mt = 100
IP4.ROUTE[2]:                           dst = 0.0.0.0/0, nh = 192.168.0.254, mt = 100
IP4.DNS[1]:                             192.168.0.254
IP4.DNS[2]:                             1.1.1.1
IP6.GATEWAY:                            --

Using ip utility

The ip command (provided by the iproute2 package) is a powerful tool to get information and configure the network of a modern Linux system such as Rocky Linux.

In this example, we will assume the following parameters:

  • interface name: ens19
  • ip address: 192.168.20.10
  • subnet mask: 24
  • gateway: 192.168.20.254

Get general information

To see the detailed state of all interfaces, use

ip a

Pro tips: * use the -c flag to get a more readable coloured output: ip -c a. * ip accepts abbreviation so ip a, ip addr and ip address are equivalent

Bring interface up or down

To bring the ens19 interface up, simply use ip link set ens19 up and to bring it down, use ip link set ens19 down.

Assign the interface a static address

The command to be used is of the form:

ip addr add <IP ADDRESS/CIDR> dev <IFACE NAME>

To assign the above example parameters, we will use:

ip a add 192.168.20.10/24 dev ens19

Then, checking the result with:

ip a show dev ens19

will output:

3: ens19: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 4a:f2:f5:b6:aa:9f brd ff:ff:ff:ff:ff:ff
    inet 192.168.20.10/24 scope global ens19
    valid_lft forever preferred_lft forever

Our interface is up and configured, but is still lacking something!

Using ifcfg utility

To add the ens19 interface our new example IP address, use the following command:

ifcfg ens19 add 192.168.20.10/24

To remove the address:

ifcfg ens19 del 192.168.20.10/24

To completely disable IP addressing on this interface:

ifcfg ens19 stop

Note that this does not bring the interface down, it simply unassigns all IP addresses from the interface.

Gateway configuration

Now that the interface has an address, we have to set its default route, this can be done with:

ip route add default via 192.168.20.254 dev ens19

The kernel routing table can be displayed with

ip route

or ip r for short.

Checking network connectivity

At this point, you should have your network interface up and properly configured. There are several ways to verify your connectivity.

By pinging another IP address in the same network (we will use 192.168.20.42 as an example):

ping -c3 192.168.20.42

This command will issue 3 pings (known as ICMP request) and wait for a reply. If everything went fine, you should get this output:

PING 192.168.20.42 (192.168.20.42) 56(84) bytes of data.
64 bytes from 192.168.20.42: icmp_seq=1 ttl=64 time=1.07 ms
64 bytes from 192.168.20.42: icmp_seq=2 ttl=64 time=0.915 ms
64 bytes from 192.168.20.42: icmp_seq=3 ttl=64 time=0.850 ms

--- 192.168.20.42 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 5ms
rtt min/avg/max/mdev = 0.850/0.946/1.074/0.097 ms

Then, to make sure your routing configuration is fine, try to ping a external host, such as this well known public DNS resolver:

ping -c3 8.8.8.8

If your machine has several network interface and you want to make ICMP request via a specific interface, you can use the -I flag:

ping -I ens19  -c3 192.168.20.42

It is now time to make sure that DNS resolution is working correctly. As a reminder, DNS resolution is a mechanism used to convert human friendly machine names into their IP addresses and the other way round (reverse DNS).

If the /etc/resolv.conf file indicates a reachable DNS server, then the following should work:

host rockylinux.org

The result should be:

rockylinux.org has address 76.76.21.21
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