Chapter 1. General RHEL networking topics

This section provides details about general networking topics.

1.1. The difference between IP and non-IP networks

A network is a system of interconnected devices that can communicate sharing information and resources, such as files, printers, applications, and Internet connection. Each of these devices has a unique IP address to send and receive messages between two or more devices using a set of rules called protocol.

Categories of network communication:

IP networks
Networks that communicate through IP addresses. An IP network is implemented in the Internet and most internal networks. Ethernet, wireless networks, and VPN connections are typical examples.
Non-IP networks
Networks that are used to communicate through a lower layer rather than the transport layer. Note that these networks are rarely used. For example, InfiniBand is a non-IP network.

1.2. The difference between static and dynamic IP addressing

Static IP addressing

When you assign a static IP address to a device, the address does not change over time unless you change it manually. Use static IP addressing if you want:

  • To ensure network address consistency for servers such as DNS, and authentication servers.
  • To use out-of-band management devices that work independently of other network infrastructure.
Dynamic IP addressing

When you configure a device to use a dynamic IP address, the address can change over time. For this reason, dynamic addresses are typically used for devices that connect to the network occasionally because the IP address can be different after rebooting the host.

Dynamic IP addresses are more flexible, easier to set up, and administer. The Dynamic Host Control Protocol (DHCP) is a traditional method of dynamically assigning network configurations to hosts.

Note

There is no strict rule defining when to use static or dynamic IP addresses. It depends on user’s needs, preferences, and the network environment.

Additional resources

For details about setting up a DHCP server, see Chapter 39, Providing DHCP services.

1.3. DHCP transaction phases

The DHCP works in four phases: Discovery, Offer, Request, Acknowledgement, also called the DORA process. DHCP uses this process to provide IP addresses to clients.

Discovery

The DHCP client sends a message to discover the DHCP server in the network. This message is broadcasted at the network and data link layer.

Offer

The DHCP server receives messages from the client and offers an IP address to the DHCP client. This message is unicast at the data link layer but broadcast at the network layer.

Request

The DHCP client requests the DHCP server for the offered IP address. This message is unicast at the data link layer but broadcast at the network layer.

Acknowledgment

The DHCP server sends an acknowledgment to the DHCP client. This message is unicast at the data link layer but broadcast at the network layer. It is the final message of the DHCP DORA process.

1.4. InfiniBand and RDMA networks

For details about InfiniBand and Remote Direct Memory Access (RDMA) networks, see the Configuring InfiniBand and RDMA networks documentation.

1.5. Legacy network scripts support in RHEL

By default, RHEL uses NetworkManager to configure and manage network connections, and the /usr/sbin/ifup and /usr/sbin/ifdown scripts use NetworkManager to process ifcfg files in the /etc/sysconfig/network-scripts/ directory.

However, if you require the deprecated network scripts that processes the network configuration without using NetworkManager, you can install them:

# yum install network-scripts

After you have installed the legacy network scripts, the /usr/sbin/ifup and /usr/sbin/ifdown scripts link to to the deprecated shell scripts that manage the network configuration.

Important

The legacy scripts are deprecated in RHEL 8 and will be removed in a future major version of RHEL. If you still use the legacy network scripts, for example, because you upgraded from an earlier version to RHEL 8, Red Hat recommends that you migrate your configuration to NetworkManager.

1.6. Selecting network configuration methods

  • To configure a network interface using NetworkManager, use one of the following tools:

    • the text user interface, nmtui.
    • the command-line utility , nmcli.
    • the graphical user interface tools, GNOME GUI.
  • To configure a network interface without using NetworkManager tools and applications:

    • edit the ifcfg files manually. Note that even if you edit the files directly, NetworkManager is the default on RHEL and processes these files. Only if you installed and enabled the deprecated legacy networking scrips, then these scripts process the ifcfg files.
  • To configure the network settings when the root file system is not local:

    • use the kernel command-line.