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Linode
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Computer networks frequently use DHCP to assign IP addresses, routing and DNS information to systems which join the network. Additional IPs can be assigned to virtual network interfaces for a fully static IP address configuration, including multiple static addresses.
multiple ip addresses,linux static ip,change ip address,network configuration,dns,DHCP
networking/configuring-static-ip-interfaces/
Wednesday, June 1st, 2016
name
Linode
Thursday, July 20th, 2014
Linux Static IP Configuration

Network configurations are generally assigned to a networked device in one of two methods, either by DHCP or static assignments. These terms (and others) are often used when discussing IP addresses. Besides IPs, a basic network interface configuration usually needs DNS resolvers and routing as well.

Upon a Linode's creation, an IPv4 address is selected from a pool of available addresses from the datacenter in which your Linode is hosted. Our Network Helper is enabled by default for new Linodes. This means that when you deploy a Linux distribution to your Linode and boot it, the host system detects which distro was selected and modifies the network configuration files in the disk image to statically configure the Linode's IPv4 addresses, routing and DNS. Network Helper does not work with IPv6, so v6 addresses are assigned via SLAAC during deployment.

If Network Helper is disabled (or if your Linode was created before Network Helper became default), a Linode will be assigned its IPv4 network configuration by DHCP from the datacenter's networking hardware. One limitation of DHCP is that it can only assign one IP address per DHCP lease request. If you want additonal IPs for your Linode, static addressing must be used.

Due to the limited availablilty of IPv4 addresses, additional v4 addresses for your Linode must be requested by contacting support with a technical justification. Once approved, v4 addresses can be added through the Remote Access tab of the Linode Manager. Additional IPv6 addresses are also available by submitting a support ticket.

An alternative to using the Linode Manager for static addressing is to manually configure within your Linux distribution. This alternative method will be the focus of this guide. Be aware that errors in network configurations can disconnect SSH sessions, so it is advised that you use the Linode Shell (Lish) when making the changes below.

General Network Configuration

Log in to the Linode Manager and go to the Remote Access tab. From there you will see your Linode's:

  • IPv4 and IPv6 addresses (both private and public)
  • Netmask
  • Default IPv4 gateway
  • DNS resolvers

Keep this information handy because you'll need it as you configure your Linode's network settings.

Linode Manager / Remote Access

{: .note}

Each Linode has only one virtual ethernet interface, eth0. Most outbound connections will still originate from the IP assigned to eth0, but if you need server daemons to bind to a particular IP address, you'll need to specify the correct IP in their configuration files.

Static Network Configuration

Addressing

The different IP blocks available to your Linode are:

  • Public IPv4 - /24
  • Private IPv4 - /17
  • IPv6 - /64

{: .note}

Some Linux distributions determine their netmask based on the assigned IP address block.

Gateway

Although your Linode may have multiple IP addresses assigned using virtual interfaces, you should only specify a default gateway for one interface. The gateway should be on the same network as the desired IP address. For example, if you have the interface eth0:3 assigned to the address 198.51.100.5, you should use 198.51.100.1 as the gateway.

A default gateway should not be specified for private IP addresses. Additionally, the subnet mask for private IPs should be set to 255.255.128.0, not 255.255.255.0.

DNS Resolution

Your DNS nameservers are listed under the Remote Access tab of the Linode Manager (see the screenshot above). With exception to specific situations, you should not change your Linode's nameservers by editing /etc/resolv.conf. Depending on your distribution, resolv.conf may be overwritten frequently, so permanent DNS and resolver configuration options are usually intended to be set elsewhere.

For more info on resolv.conf, see its manual page.

{: .caution}

Using the examples below, be sure the IP addresses you enter reflect those shown under the Remote Access tab of the Linode Manager.

Arch

Add the following addressing to the interface's configuration.

{: .file-excerpt } /etc/systemd/network/05-eth0.network : ~~~ conf [Match] Name=eth0

[Network]
Gateway=198.51.100.1

# Your primary public IP address
Address=198.51.100.2/24

# To add a second public IP address:
Address=198.51.100.3/24

#To add a private IP address:
Address=192.168.133.234/17
~~~

Static IP addresses can be configured multiple ways in Arch. See the Static IP Address section of Arch's Network Configuration Wiki page for other options such as using Netctl. Additionally, you can configure DNS several other ways without modifying resolv.conf.

CentOS 7 / Fedora 22+

The default ethernet interface file is located at /etc/sysconfig/network-scripts/ifcfg-eth0. You can configure a static IP address by adding or editing the following lines, substituting your own Linode's IP addresses, gateways, and DNS resolvers:

{: .file-excerpt } /etc/sysconfig/network-scripts/ifcfg-eth0 : ~~~ conf DEVICE="eth0" BOOTPROTO="static" ONBOOT="yes" IPV6INIT="yes" IPV6_AUTOCONF="yes" NM_CONTROLLED="no" PEERDNS="no"

GATEWAY=198.51.100.1

# Your primary public IP address
# The netmask is taken from the PREFIX (where 24 is a public IP, 17 is a private IP)
IPADDR0=198.51.100.5
PREFIX0="24"

# To add a second public IP address:
IPADDR1=198.51.100.10
PREFIX1="24"

# To add a private IP address:
IPADDR2=192.0.2.6
PREFIX2="17"

DOMAIN=members.linode.com

DNS1=203.0.113.1
DNS2=203.0.113.2
DNS3=203.0.113.3
~~~

To load your changes, restart the network service:

sudo systemctl restart network

{: .note}

CentOS 7 and recent versions of Fedora also include NetworkManager, which uses tools such as nmtui and nmcli to modify and create network configuration files. The above method to make the necessary modifications, however, is more straightforward.

CentOS 6

Like in CentOS 7, simply edit the ethernet interface file to configure a static IP address:

{: .file-excerpt } /etc/sysconfig/network-scripts/ifcfg-eth0 : ~~~ conf BOOTPROTO=none PEERDNS=no

# Your primary static public IP address.
IPADDR0=198.51.100.5
PREFIX0=24
GATEWAY=198.51.100.1
DOMAIN=members.linode.com
DNS1=203.0.113.1
DNS2=203.0.113.2
DNS3=203.0.113.3
~~~

To add the resolv.conf option to rotate DNS providers, create a dhclient script:

{: .file } /etc/dhcp/dhclient.d/rotate.sh : ~~~ conf rotate_config() { echo "options rotate" >> /etc/resolv.conf }

rotate_restore() {
    :
}
~~~

For multiple static IP addresses, additional IPs are assigned to an alias you create for eth0. To use this alias, an additional file must be created. For example, an eth0:1 file must be created for the eth0:1 interface alias, eth0:2 for eth0:2, etc.

{: .file } /etc/sysconfig/network-scripts/ifcfg-eth0:1 : ~~~ conf # Add a second static public IP address. DEVICE=eth0:1 IPADDR=198.51.100.10 ~~~

To put any changes into effect, restart your networking service:

sudo service network restart

For more information on the options available to interface files, see man ifcfg and Fedora's documentation and the file /usr/share/doc/initscripts-*/sysconfig.txt on CentOS and Fedora installations.

Debian / Ubuntu

Add the following to the interface's configuration file:

{: .file-excerpt } /etc/network/interfaces : ~~~ conf . . .

# Your primary public IP address.
auto eth0
iface eth0 inet static
    address 198.51.100.5/24
    gateway 198.51.100.1
    dns-nameservers 203.0.113.1 203.0.113.2 203.0.113.3
    dns-search members.linode.com
    dns-options rotate

# To add a second public IP address:
iface eth0 inet static
    address 198.51.100.10/24

# To add a private IP address:
iface eth0 inet static
    address 192.0.2.6/17
~~~

Note that static and dynamic addressing cannot be combined in Debian and Ubuntu systems. In order to statically configure additional IP addresses, you must also statically configure your default IP address.

Gentoo

Networking in Gentoo utilizes the netifrc utility. Addresses are specified in the config_eth0 line and separated by spaces. The gateway is defined in the routes_eth0 line.

{: .file-excerpt } /etc/conf.d/net : ~~~ conf config_eth0="198.51.100.5/24 198.51.100.10/24 192.0.2.6/17" routes_eth0="default via 198.51.100.1" . . . ~~~

OpenSUSE

  1. Edit the interface's config file with:

    {: .file-excerpt } /etc/sysconfig/network/ifcfg-eth0 : ~~~ conf BOOTPROTO=static

    . . .

    # Your primary public IP address. IPADDR=198.51.100.5/24 GATEWAY=198.51.100.1

    # Add a second public IP address: IPADDR1=198.51.100.10/24 LABEL1=1

    # Add a private IP address: IPADDR2=192.0.2.6/17 LABEL2=2

    
    2.  You will also need to add your gateway to the network routes file:
    
    {: .file }
    /etc/sysconfig/network/routes
    : ~~~
      # Destination   Gateway                 Netmask                 Device
      default         198.51.100.1            -                       eth0
    
  2. Edit each line to add DNS and domain information for netconfig. Netconfig uses this info to modify resolv.conf:

    {: .file-excerpt } /etc/sysconfig/network/config : ~~~ . . . NETCONFIG_DNS_STATIC_SERVERS="203.0.113.1 203.0.113.2 203.0.113.3" . . . NETCONFIG_DNS_STATIC_SEARCHLIST="members.linode.com" . . . NETCONFIG_DNS_RESOLVER_OPTIONS="rotate"

    
    ## Disable Network Helper
    
    When statically configuring IP addresses, [Network Helper](/docs/platform/network-helper) should be disabled to avoid its overwriting your interface's configuration file in the future.
    
    1.  From the Linode Manager's **Dashboard**, choose **Edit** for the desired configuration profile.
    
    [![Linode Manager: Dashboard > Configuration Profile > Edit](/docs/assets/linode-dashboard-hilighted_small.png)](/docs/assets/linode-dashboard-hilighted.png)
    
    2.  Scroll to the **Filesystem/Boot Helpers** section at the bottom of the page. The radio button for **Auto-configure Networking** should be set to **Yes** to indicate Network Helper is enabled. To disable it, select **No** and click **Save Changes**.
    
    [![Linode Manager: Dashboard > Configuration Profile > Edit](/docs/assets/network-helper-hilighted_small.png)](/docs/assets/network-helper-hilighted.png)
    
    
    ## Reboot Your Linode
    
    It's best to reboot your Linode from the dashboard of the Linode Manager rather than use `ifconfig` or an init system to restart the interfaces or a distro's network services. Rebooting ensures that the new settings take effect without issues and that the networking services reliably start in full from the boot-up.
    
    ## Test Connectivity
    
    1.  Log back into your Linode through SSH.
    
    2.  Confirm that your `/etc/resolv.conf` exists and is correct.
    
    3.  Ping each default IPv4 gateway listed on the **Remote Access** tab of the Linode Manager and ping a domain to confirm DNS resolution works:
    
        ping -c 3 198.51.100.1
        ping -c 3 *some_domain*.com