Guides - Network Configuration Using NetworkManager

NetworkManager is a very popular network configuration utility and is used by default on Fedora, CentOS Stream, CentOS, AlmaLinux 8, and Rocky Linux 8. It can also be easily installed on Arch, Ubuntu, and other distributions.

Configuration Files

Most distributions that use NetworkManager enable the ifcfg-rh plugin be default, which allows NetworkManager to use the older ifcfg configuration file format. NetworkManager also supports its own native keyfile format. By default, Network Helper uses the ifcfg format, so that is what this guide covers.

• File location: /etc/sysconfig/network-scripts/
• Naming convention: ifcfg-[interface], replacing [interface] with the name of the interface you wish to configure.
• Default configuration file: /etc/sysconfig/network-scripts/ifcfg-eth0

Starter Configuration

Here is an example of a typical configuration file for NetworkManager. It statically defines the IPv4 address and allows SLAAC to configure the IPv6 address.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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DEVICE="eth0" NAME="eth0" ONBOOT="yes" BOOTPROTO="none" IPV6INIT="yes" IPV6_ADDR_GEN_MODE="eui64" IPV6_PRIVACY="no" PEERDNS="no" DOMAIN=ip.linodeusercontent.com DNS1=203.0.113.1 DNS2=203.0.113.2 DNS3=203.0.113.3 GATEWAY0=192.0.2.1 IPADDR0=192.0.2.123 PREFIX0=24

Configuring IP Addresses Manually

1. Log in to Cloud Manager and review your Compute Instance’s IP addresses. See Managing IP Addresses. Make a note of the following pieces of information or keep this page accessible so you can reference it later.

   • Public IPv4 address(es) and the associated IPv4 gateway
   • Private IPv4 address (if one has been added)
   • IPv6 SLAAC address and the associated IPv6 gateway
   • IPv6 /64 or /56 routed range (if one has been added)
   • DNS resolvers (if you want to use Linode’s resolvers)

2. Disable Network Helper on the Compute Instance so that it doesn’t overwrite any of your changes on the next system reboot. For instructions, see the Network Helper guide. This guide covers disabling Network Helper globally (for all Compute Instances on your account) or just for a single instance.

3. Log in to the Compute Instance using SSH or Lish. You may want to consider using Lish to avoid getting locked out in the case of a configuration error.

4. Perform any necessary configuration steps as outlined in the workflows below. You can edit your network configuration file using a text editor like nano or vim.

   sudo nano /etc/sysconfig/network-scripts/ifcfg-eth0

5. Once you’ve edited the configuration file to fit your needs, you need to apply the changes or reboot the Compute Instance. To apply your changes with NetworkManager, run the following commands:

   sudo nmcli connection reload
   sudo nmcli connection down eth0
   sudo nmcli connection up eth0

Changing the Primary IPv4 Address

To change the main IPv4 address configured on the system, set the GATEWAY0, ADDRESS0, and PREFIX0 parameters to match the new IP address and its corresponding gateway IP address.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... GATEWAY0=192.0.2.1 IPADDR0=192.0.2.123 PREFIX0=24

Configuring the Primary IPv4 Address through DHCP

DHCP can be used to automatically configure your primary IPv4 address. The primary IPv4 address is defined as the IPv4 address assigned to your system that is in the first position when sorted numerically. To enable DHCP, set the BOOTPROTO parameter to "dhcp" and remove (or comment out) the lines that define the GATEWAY0, ADDRESS0, and PREFIX0 parameters.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... BOOTPROTO="dhcp" ... # GATEWAY0=192.0.2.1 # IPADDR0=192.0.2.123 # PREFIX0=24

To disable DHCP, set the BOOTPROTO parameter back to "none".

Configuring Additional IPv4 Addresses

Additional IPv4 addresses can be configured by adding the IPADDRn and PREFIXn parameters, where n is an incrementing number based on how many other IPv4 address you have configured (starting at 0 for the primary address). For instance, to add a second IPv4 address, use the parameters IPADDR1 and PREFIX1. For a third address, use IPADDR2 and PREFIX2.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... IPADDR1=[ip-address] PREFIX1=[prefix]

In the example above, make the following replacements:

• [ip-address]: The IPv4 address that you wish to statically configure.
• [prefix]: The prefix is based on the type of IP address you are adding. It should be 24 for public IPv4 addresses and 17 for private IPv4 addresses.

Configuring the Primary IPv6 Address through SLAAC

SLAAC is used to automatically configure your primary IPv6 address. For this to work, your system must accept router advertisements. You also may need to disable IPv6 privacy extensions. Within NetworkManager, you can set IPV6INIT to yes, IPV6_ADDR_GEN_MODE to eui64, and IPV6_PRIVACY to no.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... IPV6INIT="yes" IPV6_ADDR_GEN_MODE="eui64"

If you wish to disable IPv6 SLAAC addressing and instead statically configure your IPv6 address (not recommended), you can explicitly set the net.ipv6.conf.eth0.autoconf kernel variable to 0 in the /etc/sysctl.conf file and then reboot your Compute Instance

File: /etc/sysctl.conf

1 2	... net.ipv6.conf.all.autoconf=0

Then modify the network configuration file to disable auto-configuration and statically set your IPv6 address (using the prefix of /128).

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... IPV6INIT="yes" IPV6_AUTOCONF="no" # IPV6_ADDR_GEN_MODE="eui64" # IPV6_PRIVACY="no" IPV6ADDR=[ip-address]/128 IPV6_DEFAULTGW=fe80::1

Configuring Additional IPv6 Addresses

If you have an IPv6 range assigned to your Compute Instance, addresses from this range can be configured through the IPV6ADDR_SECONDARIES parameter. This accepts a list of space delimited IPv6 addresses.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

1 2	... IPV6ADDR_SECONDARIES="[ip-address]/[prefix]"

In the example above, make the following replacements:

• [ip-address]: The IPv6 address that you wish to statically configure. You can choose any address within your available range. For example, within the range 2001:db8:e001:1b8c::/64, the address 2001:db8:e001:1b8c::1 can be used.
• [prefix]: The prefix should either be 64 or 56 (depending on the size of your IPv6 range)

Changing the DNS Resolvers

DNS resolvers are the entities that resolve domain names to their corresponding IPv4 address. By default, the Compute Instance should be using the DNS resolvers for the data center in which it resides. You can change these by setting the DNS parameter to a space delimited list of the IP addresses for your preferred DNS resolvers.

File: /etc/sysconfig/network-scripts/ifcfg-eth0

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... DNS1=203.0.113.1 DNS2=203.0.113.2 DNS3=203.0.113.3

In the above example, replace the IP addresses provided with the IP addresses of the DNS resolvers you wish to use. Both IPv4 and IPv6 addresses can be used together.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• NetworkManager documentation