To add an additional network interface to an instance or to remove an interface from your instance perform the steps described below.

Please note: The steps below only provide a basic overview. The exact tasks required will vary depending on your network design. Please refer to the Azure documentation for details.

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Adding an Additional Network Interface

It is possible to add additional NICs to the Charon host system in the cloud. Additional NICs can be used to connect the instance to additional subnets. And an additional NIC can also be used to provide an emulated SPARC system running in the emulator with a dedicated network interface. This section shows the basic steps to add a NIC to an existing Azure cloud instance.

Please note: The VM must be stopped before the new interface can be attached to the system. The VM also must be stopped before detaching an interface.

To add an existing or newly created NIC to the Charon host cloud instance, perform the following steps:

Step 1: Open the Networking screen of your Charon host cloud instance. The sample below shows a VM with only one NIC.

Step 2: Click on Attach network interface at the top. This will either let you choose an existing interface or offer the option to create a new one as shown in the sample below:

Step 3: Click on Create network interface to open the interface creation screen.

Add the mandatory information:

• Name
• Subnet
• Private IP (if static IP is selected)
• Resource group (same as VM)

Once the information has been added, click on Create to create the new NIC. This will return you to the Networking screen.

Step 4: Attach the selected or newly created interface to your cloud VM.

Please note: make sure to stop the instance before attaching the interface.

On the Networking screen, you should now see the new interface (if required, open the subsection of the screen by clicking on
Attach network interface). Click on OK to add the NIC to your VM. The image below shows an example:

The Networking screen should now show the two interfaces in two different tabs, as displayed below:

Step 5: Restart your VM, log in and check the availability of the second interface.

The output of the ip link show command now shows the second interface (eth1 in the example).

[root@we-test-vm1 charon]# ip link show |grep eth
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 00:0d:3a:8f:da:f2 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000

Note that for the new interface DHCP or another IP configuration on the host operating system level is not active automatically. Depending on the underlying Linux version, an ifcfg file for the interface has to be created manually in /etc/sysconfig/network-scripts/ (mostly Linux 7.x) or set up via nmcli or nmtui (mostly Linux 8.x).

Adding a Public IP address to the Second NIC

Please note: If this NIC is used as a dedicated NIC for a legacy guest operating system, it is not recommended to expose the legacy guest operating system to the Internet by adding a public IP to the dedicated NIC. It is highly recommended to use a secure, encrypted VPN connection for any external traffic of the guest system. The user is responsible for making sure that any external connection complies with the relevant rules and policies of the environment.

Creating a Public IP Address

A public IP address is a resource that can be created using the Create a resource icon on the Home screen. On the overview page, search for public IP address. This will open the initial screen to create public IP address:

Clicking on Create takes you to the IP address configuration screen:

Add the necessary data, in particular the following:

• Name
• Dynamic (changes every time the instance is restarted) or Static (persistent)
• Resource group (same as your interface)
• Location

Click on Create to create the address resource.

Attaching the Public IP Address to an Interface

To attach the new public IP address to the second NIC of your instance, perform the following steps:

• Select your VM in the overview list.
• Go to the Networking section.
• Select the interface tab of the relevant interface.
• On the interface tab page, click on the interface name link next to the Network interface label.
• On the network interface page, under Settings (in the left-hand pane), select IP configurations.
• Click on the name of the IP configuration (in the list at the bottom of the page) to which you want to add the public IP address. This will open the IP configuration screen.

On this screen select Associate for the Public IP address. This will allow you to select the new public IP address.

Then click on Save (at the top of the section) to save the changes.

Please note: do not forget to add an appropriate Network Security Group to protect the interface.

Address Assignment Information

You can divide a VNet into multiple subnets for organization and security. Each NIC in a VM is connected to one subnet in one VNet. NICs connected to subnets (same or different) within a VNet can communicate with each other without any extra configuration. You can change the subnet a VM is connected to after it's created, but you cannot change the VNet. Each NIC attached to a VM is assigned a MAC address that doesn’t change until the VM is deleted.

Reserved addresses in each subnet:

The addresses x.x.x.0 to x.x.x.3 in every subnet and the last addresses in every subnet are reserved.

• x.x.x.0: network address
  
• x.x.x.1: default gateway
  
• x.x.x.2, x.x.x.3: DNS services
  
• x.x.x.255: broadcast address
  

Please note:

• The automatically configured default router of a subnet does not respond to a ping command.
• The traceroute command does not work.
• Multicast, broadcast, and GRE are not supported.

Public IP addresses:
By default, public IP addresses are dynamic and the address associated to them may change when the VM is stopped or deleted. To ensure that the VM always uses the same public IP address, create a static public IP address. One public IP address can be assigned to an instance at instance creation. Additional public IP addresses can be created using by creating a new resource
(Home > Create a Resource > search for Public IP address and select resource > Create) and assigning the resource to an instance interface.