There are significant differences regarding the NetworkManager in the different Linux versions (RHEL 7, 8, 9 and derivatives). This section provides an overview of some important differences.

There are two basic network configuration systems in the relevant Linux systems:

The network service with the network configuration based on ifcfg-files in /etc/sysconfig/network-scripts. This requires the network-scripts package.
The NetworkManager with its own configuration file syntax. Persistent configuration files are stored in /etc/NetworkManager/system-connections. The NetworkManager has a plugin (ifcfg-rh) to handle ifcfg-files. This plugin does not support all configuration options of the network-scripts system (e.g., tunnel and tap interfaces are not supported).

Linux 7.x:

The network-scripts and NetworkManager methods coexist. It is possible to disable the NetworkManager completely or only for certain interfaces (parameter NM_CONTROLLED=no in the ifcfg-file).
The default NetworkManager plugin is the ifcfg-rh plugin.
Interfaces managed by the Charon-SSP Manager must have an ifcfg-file and be removed from NetworkManager control (unmanaged interfaces).

Linux 8.x:

The network-scripts package is deprecated. It is not installed by default, but available in the Linux package repositories.
The default NetworkManager plugin configuration is ifcfg-rh, keyfile. The keyfile plugin is responsible for handling the native NetworkManager configuration file syntax.
If virtual bridge configurations including TAP interfaces are configured using ifcfg-files, the network-scripts package is required. Otherwise, the TAP interfaces cannot be activated (missing support in the ifcfg-rh plugin). Alternatively, such interfaces can be configured as native NetworkManager connections.
There is an ifup command which by default points to nm-ifup. Once the network-scripts package is installed, it points to the ifup command contained in this package.
The loopback interface (lo) cannot be managed by the NetworkManager.
Interfaces managed by the Charon-SSP Manager must be under NetworkManager control (managed interfaces).

Linux 9.x:

The network-scripts package is no longer available in the Linux package repositories.
The default Networkmanager plugin configuration is keyfile, ifcfg-rh.
Existing ifcfg-files can still be read and written, but only if supported by the ifcfg-rh plugin.
A new nmcli command option (nmcli connection migrate <con-name>) helps with the conversion of ifcfg configuration files to native NetworkManager connection profiles. However, this command only works for connections supported by the ifcfg-rh plugin. This means, for example, that TAP interfaces that were previously configured via ifcfg-files must now be recreated using nmcli commands or another NetworkManager configuration tool. Before using the migration command, take a backup copy of the content of /etc/sysconfig/network-scripts.
By default, there is no ifup command. If it is needed, the NetworkManager variant of the command can be installed (NetworkManager-initscripts-updown).
The loopback interface (lo) cannot be managed by the NetworkManager in versions before 9.2.
Interfaces managed by the Charon-SSP Manager must be under NetworkManager control (managed interfaces).

Additional information about the ifcfg-rh plugin:

The ifcfg-rh plugin is used by the NetworkManager to read/write the traditional ifcfg-files in /etc/sysconfig/network-scripts. Each NetworkManager connection corresponds to one ifcfg-file. The plugin does not support all the connection types supported by the original network-scripts package. The plugin currently supports Ethernet, Wi-Fi, InfiniBand, VLAN, Bond, Bridge, and Team connections. This means that, for example, TYPE=Tap is not supported and cannot be handled by the NetworkManager in the ifcfg-file format. In Linux 7.x and Linux 8.x, the network-scripts package can be used to support the ifcfg-file format. In Linux 9.x, this package is no longer available. Thus, unsupported connection types must be manually recreated.

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