Networking, Network Devices, and Network Management

Hostname

  • “-”, “_ “, and “. " characters are allowed.
  • Up to 253 characters.
  • Stored in /etc/hostname.

View the hostname:

hostnamectl --static
hostname
uname -n
cat /etc/hostname

Lab: Change the Hostname

Server1

  1. Open /etc/hostname and change the entry to server10.example.com
  2. restart the systemd-hostnamed service daemon
sudo systemctl restart systemd-hostnamed
  1. confirm
hostname

server2

  1. Change the hostname with hostnamectl:
sudo hostnamectl set-hostname server21.example.com

  1. Log out and back in for the prompt to update

  2. Change the hostname using nmcli

nmcli general hostname server20.example.com

IPv4

View current ipv4 address:

ip addr

Protocols

  • Defined in /etc/protocols
  • Well known ports are defined in /etc/services

ICMP

Send two pings to server 20

ping -c2 192.168.0.120

Ping the server’s loopback interface:

ping 172.0.0.1

Send a traceroute to server 20

traceroute 192.168.0.120
tracepath

ICMPv6

  • IPv6 version of ICMP
  • enabled by default

Ping and ipv6 address:

ping6

Trace a route to an IPv6 address:

tracepath6
traceroute6

Show IPv6 addresses:

ip addr | grep inet6

Misc

List all network interfaces with their ethernet addresses:

ip addr | grep ether

Connection Profiles

  • unique name for each connection profile
  • Device can have multiple connection profiles attached
    • Only one active profile per device at a time
  • Stored in /etc/sysconfig/network-scripts/
  • Filename format: ifcfg~name-of-connection~
  • connection from device to profile is established at the time of installation
  • Can manually create a connection profile and attach it to a device

Connection Profile Directives

BOOTPROTO

  • boot protocol used
  • (dhcp, none, or static)

BROWSER_ONLY

  • Works if PROXY_METHOD is set to auto.
  • Default is “no”

DEFROUTE

  • Whether to use this connection as the default route

DEVICE

  • Device name for the network interface

DNS1

  • ip or hostname of first DNS server
  • Placed in /etc/resolv.conf if PEERDNS is set to “no”

GATEWAY

  • Gateway address if BOOTPROTO is set to “none” or “static”

HWADDR

  • Hardware address

IPADDR

  • Static IP if BOOTPROTO is set to “none” or “static”

IPV4_FAILURE_FATAL

  • Disable device if IPv4 configuration fails
  • Default is “no”

IPV6INIT

  • Enable IPv6 support for this connection

NAME

  • Description for the connection
  • Default matches device name

NETMASK

  • Sets netmask address if BOOTPROTO is set to “none” or “static”

NM_CONTROLLED

  • Allows NetworkManager service to modify this connection’s config
  • Should be turned off for interfaces that use a static ip
  • Default is “yes”

ONBOOT

  • Auto activate the connection at system boot

PEERDNS

  • Tells system to update /etc/rsolv.conf
  • Default is “yes” if BOOTPROTO is set to “dhcp”

PREFIX

  • Number of subnet bits
  • May be used instead of NETMASK

PROXY_METHOD

  • Used for proxy setting
  • Default is “no”

UUID

  • UUID for this connection

TYPE

  • Type of connection (Ethernet, Wireless, etc.)

View additional directives:

man nm-settings

Naming rules for devices are governed by udevd service based on:

  • Device location
  • Topology
  • setting in firmware
  • virtualization layer

Lab: Add Network Devices to server10 and one to server20 using VirtualBox

  1. Shut down your servers (follow each step for both servers)
sudo shutdown now
  1. Add network interface in Virtualbox then power on the VMs
Select machine > settings > Network > Adapter 2 > Enable Network Adapter > Internal Network > ok
  1. Verify the new interfaces:
ip a

Administration Tools

ip

  • display monitor and manage network interfaces, routing, connections, traffic, etc.

ifup

  • Brings up an interface

ifdown

  • Brings down an interface

Lab: Configure network connection manually (server 10)

  1. Create ifcfg-enp0s8 in /etc/sysconfig/network-scripts/ and add the following directives:
TYPE=Ethernet
BOOTPROTO=static
DEFROUTE=yes
IPv4_FAILURE_FATAL=no
IPv6INIT=no
NAME=enp0s8
DEVICE=enp0s8
ONBOOT=yes
IPADDR=172.10.10.110
PREFIX=24
GATEWAY=172.10.10.1
  1. Bounce the interface:
sudo ifdown enp0s8
sudo ifup enp0s8
  1. Verify:
ip a

NetworkManager service

Default service in RHEL for network:

  • interface and connection configuration.
  • Administration.
  • Monitoring.

NetworkManager daemon

  • Responsible for keeping interfaces and connection up and active.
  • Includes:
    • nmcli
    • nmtui (text-based)
    • nm-connection-editor (GUI)
  • Does not manage loopback interfaces.

nmcli command

  • Create, view, modify, remove, activate, and deactivate network connections.
  • Control and report network device status.
  • Supports abbreviation of commands.

Operates on 7 different object categories.

  1. general
  2. networking
  3. connection (c)(con)
  4. device (d)(dev)
  5. radio
  6. monitor
  7. agent

3. connection

  • Activates, deactivates, and administers network connections.

Options:

  • show (list connections)
  • up/down (Brings connection up or down)
  • add(a) (adds a connection)
  • edit (edit connection or add a new one)
  • modify (modify properties of a connection)
  • delete(d) (delete a connection)
  • reload (re-read all connection profiles)
  • load (re-read a connection profile)

4. Device

Options:

  • status (Displays device status)
  • show (Displays info about device(s)

Show all connections, inactive or active:

nmcli c s

Deactivate the connection enp0s8:

sudo nmcli c down enp0s8

Note:

The connection profile gets detached from the device, disabling the connection.

Activate the connection enp0s8:

$ sudo nmcli c up enp0s8
# connection profile re-attaches to the device.

Display the status of all network devices:

nmcli d s

Lab: Configure New Network Connection Using nmcli (server20)

  1. Verify NetworkManager service is running:
sudo systemctl status NetworkManager
  1. Verify the interface that was added from virtualbox:
sudo nmcli d status | grep enp
  1. Add connection profile and attach it to the interface:
sudo nmcli con add type Ethernet ifname enp0s8 con-name enp0s8 ip4 172.10.10.120/24 gw4 172.10.10.1

Note:

This creates the file for the connection in /etc/sysconfig/network-scripts/
ONBOOT is set to "yes" automatically
  1. View the content of the connection profile:
cat /etc/sysconfig/network-scripts/ifcfg-enp0s8
  1. Verify ip address
ip a
  1. Deactivate the connection and detach it from the interface:
sudo nmcli c down enp0s8
  1. Verify:
nmcli c s
  1. Reactivate the connection and attach it to the interface:
sudo nmcli c up enp0s8
  1. Verify:
nmcli c s

Hosts Table

/etc/hosts

Lab: Update Hosts Table and Test Connectivity.

  1. Add both server10 and server20’s interfaces to both server’s /etc/host files:
192.168.0.110  server10.example.com  server10 <-- This is an alias
192.168.0.120  server20.example.com  server20   
172.10.10.110  server10s8.example.com   server10s8
172.10.10.120  server20s8.example.com   server20s8
  1. Send 2 packets from server10 to server20’s IP address:
ping -c2 192.168.0.120
  1. Send 2 pings from server10 to server20’s hostname:
ping -c2 server20

Lab: Add New Interface and Configure Connection Profile with nmcli

  1. Add a new network interface to server10 in virtualbox
  2. Verify the connection’s presence.
  3. Use nmcli to assign IP 192.168.0.210/24 and gateway 192.168.0.1
  4. Set the connection to auto-activate on boot.
  5. Deactivate and reactivate the connection manually.

Lab: Add New Interface and Configure Connection Profile Manually

  1. Add a new network interface to server20 in virtualbox.
  2. Verify the connection’s presence.
  3. Make a copy of /etc/sysconfig/network-scripts/ifcfg-enp0s3 as ifcfg-enp0s8 in the same directory.
  4. Remove HWADDR and UUID directives.
  5. Set values for IPADDR, NETMASK, and GATEWAY.
  6. Set the connection to auto-activate on boot.
  7. Deactivate and reactivate the connection manually.

[Review]{#part0028_split_001.html#id_460 .calibre10} Questions

1[.]{.c19}What is the use of ifup and ifdown commands?

2[.]{.c19}Which service is responsible for maintaining consistent device naming?

3[.]{.c19}List three key differences between TCP and UDP protocols.

4[.]{.c19}What is the significance of the NAME and DEVICE directives in a connection profile?

5[.]{.c19}Which class of IP addresses has the least number of node addresses?

6[.]{.c19}Which command can you use to display the hardware address of a network device?

7[.]{.c19}Define protocol.

8[.]{.c19}Which directory stores the network connection profiles?

9[.]{.c19}True or False. A network device is a physical or virtual network port and a network connection is a configuration file attached to it.

10[.]{.c23}IPv4 is a 32-bit software address. How many bits does an IPv6 address have?

11[.]{.c23}Which file defines the port and protocol mapping?

12[.]{.c23}What would the command hostnamectl set-hostname host20 do?

13[.]{.c23}Name the file that stores the hostname of the system.

14[.]{.c23}What would the command nmcli cs do?

15[.]{.c23}What is the purpose of the ONBOOT directive in the network connection profile?

16[.]{.c23}The **etchosts file maintains hostname to hardware address mappings. True or False?

17[.]{.c23}Which file contains service, port, and protocol mappings?

18[.]{.c23}What would the ip addr command produce?

19[.]{.c23}Which file would you consult to identify the port number and protocol associated with a network service?

20[.]{.c23}Adding a connection profile with the nmcli command creates a connection profile in the **etcsysconfig/network-scripts directory. True or False?

21[.]{.c23}Name four commands that can be used to display the system hostname?

22[.]{.c23}List any two benefits of subnetting.

[Answers]{#part0028_split_001.html#id_461 .calibre10} to Review Questions

1[.]{.c19}The ifup and ifdown commands are used to enable and disable a network connection, respectively.

2[.]{.c19}The udevd service handles consistent naming of network devices.

3[.]{.c19}TCP is connection-oriented, reliable, and point-to-point; UDP is connectionless, unreliable, and multi-point.

4[.]{.c19}The NAME directive sets the name for the network connection and the DEVICE directive defines the network device the connection is associated with.

5[.]{.c19}The C class supports the least number of node addresses.

6[.]{.c19}The ip command.

7[.]{.c19}A set of rules that govern the exchange of information between two network entities.

8[.]{.c19}The **etcsysconfig/network-scripts directory.

9[.]{.c19}True.

10[.]{.c23}128.

11[.]{.c23}The **etcprotocols file.

12[.]{.c23}The command provided will update the **etchostname file with the specified hostname and restart the systemd-hostnamed daemon for the change to take effect.

13[.]{.c23}The **etchostname file.

14[.]{.c23}The command provided will display the status information for all network connections.

15[.]{.c23}The purpose of the ONBOOT directive is to direct the boot scripts whether to activate this connection.

16[.]{.c23}False. This file maintains hostname to IP address mapping.

17[.]{.c23}The **etcservices file.

18[.]{.c23}This command provided will display information about network connections including IP assignments and hardware address.

19[.]{.c23}The **etcservices file.

20[.]{.c23}True.

21[.]{.c23}The hostname, uname, hostnamectl, and nmcli commands can be used to view the system hostname.

22[.]{.c23}Better manageability and less traffic.