This article shows what files to add if you want to add a bonding interface under CentOS 8 without invoking the Network manager command utility.
Our goal is to use one boding group with the name bond0 in LACP (aka 802.3ad) mode (but it could be any of the other types) with two networks 10Gbps interfaces. The setup resented here uses NetworkManager, which handles the loading of bonding module properly.

In fact, the network-scripts are now deprecated and they are missing from the system (but they still exist in the additional package – “network-scripts”, who knows till when? do not rely on them!).

The configuration files are with the same syntax as under CentOS 7, but this time the network manager parses them. The ifup and ifdown still exist and they just call the Network manager when executed (unless the “network-scripts” package is installed). If you need to enable bonding without any configuration files (for emergency situations) you may still use – How to enable Linux bonding without ifenslave

What do you need:

• Ensure you have installed: “iputils” and “NetworkManager” packages

  dnf install -y NetworkManager iputils
  

• Ensure the NetworkManager service is running

  systemctl enable NetworkManager
  systemctl start NetworkManager
  

STEP 1) Configure the bonding device

The boding interface’s name will be bond0 and the configuration will be located in /etc/sysconfig/network-scripts/ifcfg-bond0

BONDING_OPTS="mode=4 miimon=100"
TYPE=Bond
BONDING_MASTER=yes
BOOTPROTO=none
IPADDR0=192.168.0.100
PREFIX0=24
GATEWAY0=192.168.0.1
DNS1=8.8.8.8
DNS2=8.8.4.4
IPV4_FAILURE_FATAL=no
NAME=bond0
UUID=e19e2059-2e31-4143-915a-cdc11d19c9d6
DEVICE=bond0
ONBOOT=yes

As you can see we use IPADDR0, PREFIX0 and GATEWAY0, because it is easy to add multiple IPs (and gateways) with suffix 1,2,…N (just add IPADDR1,PREFIX1 and if any GATEWAY1). Add the default gateway for the system in /etc/sysconfig/network

GATEWAY=192.168.0.1

STEP 2) Configuring the network cards

Using two network cards in our bodning group we have two configuration files for each of the network interaces:
The configuration file for the first network interface ens1f0 (in your case may be with another name) is /etc/sysconfig/network-scripts/ifcfg-ens1f0:

TYPE=Ethernet
BOOTPROTO=none
NAME=ens1f0
UUID=0e747c1a-3ad6-40ef-b7d7-8358ec5f11f9
DEVICE=ens1f0
ONBOOT=yes
MASTER=bond0
SLAVE=yes

And only change the name of the second network card in the configuration file with name /etc/sysconfig/network-scripts/ifcfg-ens1f1:

TYPE=Ethernet
BOOTPROTO=none
NAME=ens1f1
UUID=c5900e93-32a0-4f58-afd6-64e09f5238a8
DEVICE=ens1f1
ONBOOT=yes
MASTER=bond0
SLAVE=yes

Of course, the UUID file should be different in all configuration files (aka devices).

STEP 3) Start the bonding network interface

Start the inteface with ifup

[root@srv ~]# ifup bond0
Connection successfully activated (master waiting for slaves) (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4)

No error and output for successful activation – now your machine may use the bond0 network interface.
The above command will start only the bonding interface, but you may want to restart the whole network:

systemctl restart NetworkManager

Or only reloading the NetworkManager configurations

nmcli connection reload

And the boding is UP and RUNNING:

[root@srv ~]# 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: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether ac:1f:6b:00:77:6e brd ff:ff:ff:ff:ff:ff
3: eno2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether ac:1f:6b:00:77:6f brd ff:ff:ff:ff:ff:ff
4: ens1f0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc mq master bond0 state UP group default qlen 1000
    link/ether 00:1b:21:cc:32:ef brd ff:ff:ff:ff:ff:ff
5: ens1f1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc mq master bond0 state UP group default qlen 1000
    link/ether 00:1b:21:cc:32:ef brd ff:ff:ff:ff:ff:ff
6: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:1b:21:cc:32:ef brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.100/24 brd 192.168.0.1 scope global noprefixroute bond0
       valid_lft forever preferred_lft forever

Troubleshooting

If you receive error of the kind even the /etc/sysconfig/network-scripts/ifcfg-bond0 exists

[root@srv ~]# ifup bond0
Error: unknown connection '/etc/sysconfig/network-scripts/ifcfg-bond0'

Just remove (comment out) the line “NM_CONTROLLED=no”. The Network manager should control the interface because the Network manager parses the configuration files unless you have not installed the deprecated network scripts – network-scripts package (which is not installed and used by default and it is unknown how long will be supported).