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

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

/etc/nsswitch.conf

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
 
10.1.1.2  myserver.com

Add DNS for eth0 with nmcli or with config file

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

OR

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

• Both methods require the NetworkManager service to be restarted for changes to take effect. (systemctl restart NetworkManager)