Configure Networking And Hostname Resolution Statically Or Dynamically

General Information

Networking has changed from RHEL 6 to 7. You can still edit network scripts in /etc/sysconfig/network-scripts/, but the “preferred” method is using front end tools that tie into the NetworkManager service.

Show IP Address of Devices

ip addr show

• ifconfig is deprecated in RHEL 7.

Show all Established Connections

ss

Show Established and Listening TCP Connections

ss -ant

flags:

• a ⇒ show both established and listening
• t ⇒ show tcp connections
• n ⇒ do not resolve service names (ports)

Other tools to use:

• ping -c 5 (send 5 pings)
• traceroute
• tracepath
• netstat - netstat has been deprecated (use ss instead), but can still be installed as part of the net-tools package

NetworkManager is the default network service in RHEL 7.

• Main Service = NetworkManager.service
• Tools to interface with NetworkManager
  • nm-connection-editor (GUI)
  • nmtui (ncurses based)
  • nmcli (cli)
• Fallback service = network.service
  • This uses the traditional network scripts in /etc/sysconfig/network-scripts/ as a fallback if NetworkManager is not in control of an interface.

Open GUI for network connections (GUI Only)

nm-connection-editor

Open text based wizard

nmtui

nmcli makes configuration changes to files in: /etc/sysconfig/network-scripts/

These files can alternatively be modified manually.

Network Device Status

nmcli dev status

Show all connection configurations

nmcli con show

• Configurations location: /etc/sysconfig/network-scripts/

Example: Create new connection (dhcp)

nmcli con add con-name "mycon" autoconnect yes type ethernet ifname eth1

Example: Create new connection (static ip)

nmcli con add con-name "mycon-static" autoconnect yes type ethernet ifname eth1 ipv4.method manual ip4 10.0.0.5/24 gw4 10.0.0.254

• The above produces the following config:
  • /etc/sysconfig/network-scripts/ifcfg-mycon-static

    TYPE=Ethernet    # from: 'type ethernet'
    BOOTPROTO=none    # from: 'ipv4.method manual'
    IPADDR=10.0.0.5    # from: 'ip4 10.0.0.5/24'
    PREFIX=24    # from: 'ipv 10.0.0.5/24'
    GATEWAY=10.0.0.254    # from: 'gw4 10.0.0.254'
    DEFROUTE=yes
    IPV4_FAILURE_FATAL=no
    IPV6INIT=yes
    IPV6_AUTOCONF=yes
    IPV6_DEFROUTE=yes
    IPV6_PEERDNS=yes
    IPV6_PEERROUTES=yes
    IPV6_FAILURE_FATAL=no
    NAME=mycon-static    # from: 'con-name "mycon-static"'
    UUID=f7e0c9af-715d-43da-9576-e6ce218d0c28
    DEVICE=eth1    # from: 'ifname eth1'
    ONBOOT=yes    # from: 'autoconnect yes'

Show only active connections

nmcli con show --active

Bring connections up/down

nmcli con down "mycon-static"
nmcli con up "mycon"

Change an existing connection's IP and Gateway

nmcli con mod eth0 ipv4.addresses 192.168.1.50/24
nmcli con mod eth0 ipv4.gateway 192.168.1.254
nmcli con mod eth0 ipv4.method manual
nmcli con up eth0

• Changes do not take place until “nmcli con up eth0”

View current hostname

hostname

Set temporary(transient) hostname

hostname myserver.domain.com
exec bash

View detailed hostname information

hostnamectl

• static hostname (stored in: /etc/hostname) - used to initialize kernel at boot (persistent)
• transient hostname - assigned temporarily due to network configuration, may revert back to static if network connectivity is lost
• pretty hostname (stored in: /etc/machine-info) - little restrictions on characters used

Set persistent(static) hostname

hostnamectl set-hostname myserver.com

Order of name resolution (hosts entry)

/etc/nsswitch.conf
 
#....other entries above
 
# hosts: search local files and then DNS
hosts:      files dns
 
#....other entries below

System wide dns name server entries (static or network manager generated)

/etc/resolv.conf
 
# Generated by NetworkManager
search us-west-2.compute.internal
nameserver 172.31.0.2

Local system hostname resolution and example entry

/etc/hosts
 
# IP      Hostname                Aliases
10.1.1.2  myserver01.example.com  website.domain.com

Add DNS (not replace) for eth0 with nmcli or with config file

• nmcli method

  nmcli con show
  (observe NAME field)
  nmcli con mod "System eth0" +ipv4.dns 8.8.8.8

• Edit files directly method

  vim /etc/sysconfig/network-scripts/ifcfg-eth0
   
  DNS1=8.8.8.8

• Apply changes: Issue nmcli command or restart NetworkManager
  • nmcli method

    nmcli con up eth0

  • Service restart

    systemctl restart NetworkManager