Adding a Public IPv4 and IPv6 Address to a Cloud Server or Virtual Private Server (Ubuntu 18.04/20.04 or Debian 10/11/12)

How to configure additional, public IPv4 and IPv6 addresses in Ubuntu 18.04, Ubuntu 20.04, Debian 10, 11, or Debian 12:

To determine the file name of the network interface, enter the following command:

[root@localhost ~]# ip addr

Example:

[root@localhost ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ens192: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:50:56:2b:2c:68 brd ff:ff:ff:ff:ff:ff
    inet 212.227.209.26/32 brd 212.227.209.26 scope global dynamic ens192
       valid_lft 33737sec preferred_lft 33737sec
    inet6 fe80::250:56ff:fe2b:2c68/64 scope link
       valid_lft forever preferred_lft forever

In this example, the name of the network interface is ens192.

• To display the DNS servers used, enter the following commands:

  [root@localhost ~]# curl http://169.254.169.254/latest/meta_data/dns/nameservers -Lv
  
  [root@localhost ~]# curl http://169.254.169.254/latest/meta_data/dns/nameservers6 -Lv

  Afterwards the DNS servers used are displayed at the end of the output. Example:

  [root@localhost ~]# curl http://169.254.169.254/latest/meta_data/dns/nameservers -Lv
  * Trying 169.254.169.254...
  * TCP_NODELAY set
  * Connected to 169.254.169.254 (169.254.169.254) port 80 (#0)
  > GET /latest/meta_data/dns/nameservers HTTP/1.1
  > Host: 169.254.169.254
  > User-Agent: curl/7.61.1
  > Accept: */*
  >
  < HTTP/1.1 200 OK
  < Date: Thu, 08 Sep 2022 12:19:36 GMT
  < Server: Apache
  < Strict-Transport-Security: max-age=63072000; includeSubDomains
  < Vary: Accept-Encoding
  < Access-Control-Allow-Origin: *
  < Access-Control-Allow-Headers: X-TOKEN, X-HASH, X-MICROTIME, X-USER, Content-Type, X-API-TOKEN, Authorization
  < Access-Control-Allow-Methods: PUT, GET, POST, DELETE, OPTIONS
  < Access-Control-Expose-Headers: Error-Msg
  < Cache-control: no-cache, no-store, max-age=0
  < Access-Control-Allow-Origin: *
  < Access-Control-Allow-Headers: X-TOKEN, X-HASH, X-MICROTIME, Content-Type, X-API-TOKEN, Authorization
  < Access-Control-Allow-Methods: PUT, GET, POST, DELETE, OPTIONS
  < Access-Control-Expose-Headers: Error-Msg
  < Transfer-Encoding: chunked
  < Content-Type: text/plain;charset=UTF-8
  <
  212.227.123.16,212.227.123.17
  * Connection #0 to host 169.254.169.254 left intact.

• Make a note of the DNS servers. In the example above, the DNS servers are displayed above the line * Connection #0 to host 169.254.169.254 left intact.
  
  If you do not see the DNS servers used after entering the command, enter the following command:

  [root@localhost ~]# resolvectl --no-pager |grep Server

  Afterwards the DNS servers used are displayed at the end of the output. Example:

  root@localhost:/etc/netplan# resolvectl --no-pager |grep Server
  Current DNS Server: 212.227.123.16
         DNS Servers: 212.227.123.16 212.227.123.17 2001:8d8:fe:53:72ec::1

• To display the default gateway of the active interface, enter the following commands:
  
  IPv4:

  [root@localhost ~]# ip route show | grep 'default'

  IPv6:

  [root@localhost ~]# ip -6 route show | grep 'default'

• Make a note of the IP addresses of the gateways. These are listed directly after the default via part. Examples:
  
  IPv4 Gateway

  [root@localhost ~]# /etc/netplan# ip route show | grep 'default'
  default via 10.255.255.1 dev ens192 proto dhcp src 82.165.247.234 metric 100

  IPv6 Gateway

  [root@localhost ~]# /etc/netplan# ip -6 route show | grep 'default'
  default via fe80::250:56ff:fe8b:5f29 dev ens192 proto ra metric 100 expires 4sec pref high

       The gateway in this example is: fe80::1

Install the net-tools package. This package is a collection of important programs for controlling the network subsystem.

To install net-tools, enter the following commands:

[root@localhost ~]# apt-get update
[root@localhost ~]# apt-get upgrade
[root@localhost ~]# apt-get install -y net-tools

• Open the file /etc/network/interfaces with the editor vi.

  [root@localhost ~]# vi /etc/network/interfaces

• Replace the existing entries with the following information:

  source /etc/network/interfaces.d/*
  
  # The loopback network interface
  auto lo
  iface lo inet loopback
  
  # The primary network interface
  allow-hotplug <Interface_Device>
  
  iface <Interface_Device> inet static
      address Main IPv4-Adresse/32
      gateway 10.255.255.1
      up route add -net 10.255.255.1 netmask 255.255.255.255 dev <Interface_Device> 
  
  iface <Interface_Device> inet6 static
      address Main IPv6-Adresse/64
      gateway fe80::1

• Replace the placeholder <Interface Device>  in all places with the interface device you determined. Then enter the main IPv4 address and the main IPv6 address.

• To configure the additional IPv4 address(es), insert the following entry(s) below the entry for the main IPv4 address:

  iface <Interface_Device> inet static
      address Additional IPv4-Address_1

  iface <Interface_Device> inet static
      address Additional IPv4-Address_2

• Replace the Additional IPv4 Address part with the desired additional IPv4 address.

• Replace the placeholder <Interface Device>  with the interface device you determined.

• To configure additional IPv6 addresses, insert the following entry(s) below the entry for the main IPv6 address:

  iface <Interface_Device> inet6 static
      address Additional IPv6-Adresse_1
      gateway fe80::1

  iface <Interface_Device> inet6 static
      address Additional IPv6-Address_2
      gateway fe80::1

• Replace the Additional IPv6 address part with the desired additional IPv6 address.

• Replace the placeholder <Interface_Device> with the interface device that you determined.
  
  The following example shows a complete entry that is used to configure the main IPv4 address, the main IPv6 address, and an additional IPv4 address and an additional IPv6 address.

  source /etc/network/interfaces.d/*
  
  # The loopback network interface
  auto lo
  iface lo inet loopback
  
  # The primary network interface
  allow-hotplug ens192
  
  iface ens192 inet static
      address 82.165.103.128/32
      gateway 10.255.255.1
      up route add -net 10.255.255.1 netmask 255.255.255.255 dev ens192 
  
  iface ens192 inet static
      address 212.227.193.228/32
  
  iface ens192 inet6 static
      address 2001:8d8:1800:334::1/64
      gateway fe80::1
  
  iface ens192 inet6 static
      address 2001:8d8:1800:334::2/64
      gateway fe80::1

• To exit vi and save the file, type the command :wq then press Enter.

To add the DNS servers, proceed as follows:

Ubuntu 18.04, Ubuntu 20.04, Debian 10 and Debian 11

• Open the file /etc/systemd/resolved.conf with the editor vi.

  [root@localhost ~]# vi /etc/systemd/resolved.conf

• Then enter the DNS servers in the following format:

  DNS=<DNS-Server1> <DNS-Server2> <DNS-Server3>

• If the # symbol is listed at the beginning of this entry, delete it. Otherwise, the setting will not be applied.

• Save the file.

• To apply the setting, run the following command:

  [root@localhost ~]# systemctl restart systemd-resolved

• To restart the server, enter the following command:

  [root@localhost ~]# systemctl reboot

• Log into the server again.

• To verify that the desired IPv4 and IPv6 addresses are configured correctly, enter the ip addr show command:

  [root@localhost ~]# ip addr show