Network Interface names
Traditional network interfacin Linux are named as eth0,eth1,eth2..
This is changed in RHEL 7 . RHEL 7 assign fixed names based on firmware, device topology and device type.
Initial 2 character
Ether interface begins with en
WLAN interface begins with wl
WWAN interface begins with ww
The next character(s) represent the type of adapter
On-board - o
Hotplug slot - s
PCI Geographical locations - p
Incorporate a MAC address - x
Finally, a Number N is used to represent an index, ID , or port.
Examples
eno1 - First embedded on-board network interface
enp2s0 - PCI card network interfcae
If the fixed name cannot determined then the tradition name such as ethN will be used.
Network Manager
In RHEL7 , Configuration of network interface is managed by a system daemon called Network Manager.For Network Manager
device - A device is network interface
connection - A connection is a collection of setting that can be configured for a device
- Only one connection can be active for any one device at a time.
- The persistent configuration are stored in /etc/sysconfig/netowork-script/ifcfg-name
- nmcli command can be used to create and edit connection files from the shell prompt
Viewing network information
The command nmcli dev status will show the status of all network devices.[root@rhel7-server1 ~]# nmcli dev status
DEVICE TYPE STATE CONNECTION
virbr0 bridge connected virbr0
enp0s3 ethernet connected enp0s3
lo loopback unmanaged --
virbr0-nic tun unmanaged --
The command nmcli con show will show a list of all connections.
[root@rhel7-server1 ~]# nmcli connection show
NAME UUID TYPE DEVICE
enp0s3 b66164cd-6dac-4f5c-af32-f742fe090608 802-3-ethernet enp0s3
virbr0 a35a0cdf-b10c-41e6-aec3-ec8de78e1b79 bridge virbr0
default 48b8ebda-6e50-4b20-affe-a7afc91e8136 802-3-ethernet --
The command nmcli con show --active will show a list of active connections.
[root@rhel7-server1 ~]# nmcli connection show --active
NAME UUID TYPE DEVICE
enp0s3 b66164cd-6dac-4f5c-af32-f742fe090608 802-3-ethernet enp0s3
virbr0 a35a0cdf-b10c-41e6-aec3-ec8de78e1b79 bridge virbr0
The see the details of the connection specify the connection ID (name)
[root@rhel7-server1 ~]# nmcli connection show "enp0s3"
...
ipv4.method: auto
ipv4.dns:
ipv4.dns-search:
ipv4.dns-options: (default)
ipv4.dns-priority: 0
ipv4.addresses:
ipv4.gateway: --
ipv4.routes:
ipv4.route-metric: -1
ipv4.ignore-auto-routes: no
ipv4.ignore-auto-dns: no
ipv4.dhcp-client-id: --
Command to show device details
[root@rhel7-server1 ~]# nmcli dev show enp0s3
GENERAL.DEVICE: enp0s3
GENERAL.TYPE: ethernet
GENERAL.HWADDR: 08:00:27:78:58:3D
GENERAL.MTU: 1500
GENERAL.STATE: 100 (connected)
GENERAL.CONNECTION: enp0s3
GENERAL.CON-PATH: /org/freedesktop/NetworkManager/ActiveConnection/0
WIRED-PROPERTIES.CARRIER: on
IP4.ADDRESS[1]: 192.168.18.10/24
IP4.GATEWAY: 192.168.18.1
IP4.DNS[1]: 192.168.18.1
IP6.ADDRESS[1]: fe80::a00:27ff:fe78:583d/64
IP6.GATEWAY:
Creating Network connections with nmcli
When creating new connection with nmcli , the order of the argument is important..
The command argument comes first and must include type and interface.
Next specify type specific argument and finally specify IP address,prefix and gateway.
Addition setting such as DNS Server are set as modifications once the connection exists.
Define a new connection name "default" which will auto connect as an Ethernet connection on the enp0s3 device using DHCP.
[root@rhel7-server1 ~]# nmcli con add con-name "default" type ethernet ifname enp0s3
Connection 'default' (48b8ebda-6e50-4b20-affe-a7afc91e8136) successfully added.
[root@rhel7-server1 ~]# nmcli con add con-name "static" type ethernet ifname enp0s3 \
autoconnect no ip4 192.168.18.100 gw4 192.168.18.1
Connection 'static' (547ba59d-6378-492b-9456-617c44f94136) successfully added.
Use the below command to change to "static" connection.
[root@rhel7-server1 ~]# nmcli connection up "static"
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4)
[root@rhel7-server1 ~]# nmcli dev status
DEVICE TYPE STATE CONNECTION
virbr0 bridge connected virbr0
enp0s3 ethernet connected static
lo loopback unmanaged --
virbr0-nic tun unmanaged --
Below command to change it back to DHCP connection
[root@rhel7-server1 ~]# nmcli connection up "default"
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/8)
[root@rhel7-server1 ~]# nmcli device status
DEVICE TYPE STATE CONNECTION
virbr0 bridge connected virbr0
enp0s3 ethernet connected default
lo loopback unmanaged --
virbr0-nic tun unmanaged --
We can get some help using the below command
[root@rhel7-server1 ~]# nmcli connection add help
Usage: nmcli connection add { ARGUMENTS | help }
ARGUMENTS := COMMON_OPTIONS TYPE_SPECIFIC_OPTIONS SLAVE_OPTIONS IP_OPTIONS [-- ([+|-]. )+]
COMMON_OPTIONS:
type
ifname | "*"
[con-name ]
[autoconnect yes|no]
[save yes|no]
[master ]
[slave-type ]
TYPE_SPECIFIC_OPTIONS:
ethernet: [mac ]
[cloned-mac ]
[mtu ]
Modifying Network connections with nmcli
nmcli con mod argument used to modify connection setting
Comparison of nm-setting and ifcfg-* directives.
nmcli con mod
|
Ifcfg-* file
|
Effect
|
ipv4.method manual
|
BOOTPROTO=none
|
IPv4 address configured statically
|
ipv4.method auto
|
BOOTPROTO=dhcp
|
Will look for configuration from DHCPv4 server.If static address also
set , will not bring those up until we have information from DHCPv4
|
Ipv4.addresses “192.0.2.1/24 192.0.2.254”
|
IPADDR0=192.0.2.1
PREFIX0=24
GATEWAY0=192.0.2.254
|
Sts static IPv4 address,Network Prefix and default gateway.
|
Ipv4.dns 8.8.8.8
|
DNS0=8.8.8.8
|
Modify /etc/resolv.conf to use this nameserver
|
Ipv4.dns-search example.com
|
DOMAIN=example.com
|
Modify /etc/resolv.conf to use this domain in the search directive.
|
Ipv4.ignore-auto-dns true
|
PEERDNS=no
|
Ignore DNS server information from DHCP server
|
Connection.autoconnect yes
|
ONBOOT=yes
|
Automatically activates this connection at boot
|
Connection.id eth0
|
NAME=eth0
|
The name of this connection is eth0
|
Connection.interface-name eth0
|
DEVICE=eth0
|
The connection is bound to the network interface with this name
|
802-3-ethernet.mac-address …
|
HWADDR=…
|
The connection is bound to the network interface with this MAC
Address
|
Examples
Turn off autoconnect
[root@rhel7-server1 ~]# nmcli connection mod "static" connection.autoconnect no
Specify a DNS server
[root@rhel7-server1 ~]# nmcli con mod "static" ipv4.dns 192.168.18.1
[root@rhel7-server1 ~]# nmcli connection show static | grep -w ipv4.dns:
ipv4.dns: 192.168.18.1
Adding a secondary DNS.
We can add or remove by using "+" or "-' in front of the argument.
[root@rhel7-server1 ~]# nmcli con mod "static" +ipv4.dns 8.8.8.8
[root@rhel7-server1 ~]# nmcli connection show static | grep -w ipv4.dns:
ipv4.dns: 192.168.18.1,8.8.8.8
To modify the IP address and gateway
[root@rhel7-server1 ~]# nmcli con mod "static" ipv4.addresses "192.168.18.101/24" \
ipv4.gateway "192.168.18.1"
Adding secondary IP address without gateway
[root@rhel7-server1 ~]# nmcli con mod static +ipv4.addresses 192.168.18.100/24
[root@rhel7-server1 ~]# nmcli con show "static" | grep -w ipv4.addresses:
ipv4.addresses: 192.168.18.101/24, 192.168.18.100/24
Summary
| Command | Use |
| nmcli dev status | List all devices |
| nmcli con show | List all connections |
| nmcli con up
"ID |
Activate a connection |
| nmcli con down
"ID |
Deactivate
a connection . The connection will restart if autoconnect is yes |
| nmcli dev dis DEV |
Bring down an interface and temp disable autoconnect. |
| nmcli net off | Disable all managed interfaces |
| nmcli con add | Add a new connection |
| nmcli con mod
"ID |
Modify a connection |
| nmcli con del
"ID |
Delete a connection |
Editing Network configuration files
Network configuration files are place in /etc/sysconfig/network-scripts
[root@rhel7-server1 ~]# ll /etc/sysconfig/network-scripts/ifcfg-*
-rw-r--r--. 1 root root 312 Dec 14 00:12 /etc/sysconfig/network-scripts/ifcfg-default
-rw-r--r--. 1 root root 310 Dec 14 00:12 /etc/sysconfig/network-scripts/ifcfg-enp0s3
-rw-r--r--. 1 root root 254 Sep 12 2016 /etc/sysconfig/network-scripts/ifcfg-lo
-rw-r--r--. 1 root root 437 Dec 14 00:24 /etc/sysconfig/network-scripts/ifcfg-static
Edit the network configuration files
[root@rhel7-server1 ~]# echo "IPADDR2=192.168.18.200" >> /etc/sysconfig/network-scripts/ifcfg-static
[root@rhel7-server1 ~]# echo "PREFIX2=24" >> /etc/sysconfig/network-scripts/ifcfg-static
Reload the configuration chagnes
[root@rhel7-server1 ~]# nmcli con reload
Restart the connection with new setting
[root@rhel7-server1 ~]# nmcli con up "static"
Check the ip address details
[root@rhel7-server1 ~]# ip addr show enp0s3
2: enp0s3: mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 08:00:27:78:58:3d brd ff:ff:ff:ff:ff:ff
inet 192.168.18.100/24 brd 192.168.18.255 scope global enp0s3
valid_lft forever preferred_lft forever
inet 192.168.18.101/24 brd 192.168.18.255 scope global secondary enp0s3
valid_lft forever preferred_lft forever
inet 192.168.18.200/24 brd 192.168.18.255 scope global secondary enp0s3
valid_lft forever preferred_lft forever
inet6 fe80::455e:6fdd:ed5f:eff4/64 scope link
valid_lft forever preferred_lft forever
