Managing Network Configurations

IPv4 Networking

Wikipedia -IPv4

IPv6 Networking

Wikipedia - IPv6

Purpose	Example	Description
localhost	::1/128	Loopback address (equivalent to 127.0.0.1 in IPv4)
unspecified	::	Used to refer to all ip addresses
default route	::/0	IPv6 default route (equivalent to 0.0.0.0/0 in IPv4)
global unicast	2000::/3	IPv6 addresses currently being allocated
unique local	fd00::/8	Addresses for internal use like 192.168.0.0
link local	fe80::/10	Non-routable auto assigned for internal use
multicast	ff00::/8	Multicast addresses

NIC Naming

Red Hat - NIC naming

Show current devices

ip link show
# or, equivalently
ip link
# or, equivalently
ip l

Show current device configuration

ip addr show
# or, equivalently
ip addr
# or, equivalently
ip a

Defining Host Names and Host Name Resolution

• The hostname is written to /etc/hostname
• To resolve hostnames, /etc/hosts is used
  • 10.0.0.15 server2.example.com server2
• /etc/resolv.conf contains DNS client configuration
• The order of host name resolution is determined through /etc/nsswitch.conf

Set the system hostname

hostnamectl hostname rhel10

Add hostname to /etc/hosts for resolution

127.0.0.1 localhost rhel10 rhel10.example.com
10.0.0.15 rhel10 rhel10.example.com

Analyzing Network Configuration

• The ip tool can be used to manage all aspects of IP networking
• It replaces the legacy ifconfig tool, do not use it anymore
• Use ip addr to manage address properties
  • ip addr add dev ens33 10.0.0.10/24
• Use ip link to show link properties
  • ip -s link
• Use ip route to manage route properties
  • ip route show
  • ip route add default via 10.0.0.1
• Any changes made with the ip command will not be persistent

Network Manager

Wikipedia - NetworkManager

• NetworkManager is the systemd service that manages network configuration
• Configuration is stored in file /etc/NetworkManager/system-connections
• Different applications are available to interface with NetworkManager
  • nmcli is a powerful command line interface
  • nmtui offers a convenient text user interface
  • GNOME offers graphical tools as well
• In NetworkManager, devices are network interfaces
• Connections are collections of configuration settings for a device, stored in the configuration file in /etc/NetworkManager/system-connections
• Only one connection can be active for a device
• Permissions to modify settings in NetworkManager are applied through dbus
• Non-privileged users that are logged in on the console can change network settings
• Non-privileged users that are logged through ssh cannot change network settings
• Use nmcli general permissions for an overview of current permissions that apply

Managing Network Configuration with nmcli

Note: this is a powerful tool, but it is not on the RHCSA exam.

• nmcli has awesome tab completion
• nmcli con show shows current connections
• nmcli dev status shows current network devices
• nmcli con show {con-name} shows all connection settings
• nmcli con mod will modify connection settings: use tab completion!
• nmcli con reload will reload the modified connection

Adding a new connection is complex

nmcli con add con-name mynewconnection ifname ens33 ipv4.addresses 10.0.0.10/24 ipv4.gateway 10.0.0.1 ipv4.method manual type ethernet

• Use ipv4.method manual on connections that don’t use DHCP
• Without this setting, a DHCP server will be contacted, even if static configuration has been set

Managing Network Configuration with nmtui

• Use nmtui to save time on the exam

Troubleshooting Networking

• Use ping to verify connectivity
  • ping -c 4 archlinux.org sends 4 packets then stops
• Use ping6 to ping an IPv6 address
  • When using ping6 on link-local addresses, you must include the NIC name in the command
    • e.g. ping6 ff02::1%ens33
• ip route prints the routing table
• ip -6 route shows the IPv6 routing table
• tracepath example.com shows the entire networking path
• tracepath6 example.com shows the entire IPv6 networking path
• ss is used to analyze socket statistics
  • ss -tu
  • ss -tuna
  • ss -tunap
  • ss -tulnp

Lab Exercise

• Set the hostname for your server to rhcsaserver.example.com
• Set your server to a fixed IP address that matches your current network configuration
• Also set a second IP address 10.0.0.10/24 on the same network interface
• Enable host name resolution for your local server hostname
• Reboot and verify your network is still working with the new settings