updated Debian section

Author: asudbring

includes/virtual-network-multiple-ip-addresses-os-config.md

@@ -444,44 +444,62 @@ ip route add default via 10.0.0.1 dev eth2 table custom
 <details>
   <summary>Expand</summary>
 
+We recommend looking at the latest documentation for your Linux distribution. 
+
 1. Open a terminal window.
-1. Make sure you're the root user. If you are not, enter the following command:
+
+2. Ensure you're the root user. If you aren't, enter the following command:
 
    ```bash
    sudo -i
    ```
 
-1. Update the configuration file of the network interface (assuming ‘eth0’).
+3. Update the configuration file of the network interface (assuming **‘eth0’**).
 
-   * Open the network interface file using below command:
+   * Keep the existing line item for dhcp. The primary IP address remains configured as it was previously.
+   
+   * Add a configuration for an additional static IP address with the following commands:
 
      ```bash
-     vi /etc/network/interfaces
+     cd /etc/network/interfaces.d/
+     ls
      ```
 
-   * You should see the following lines at the end of the file:
+     You should see a .cfg file.
 
-      ```bash
-      auth eth0
-      iface eth0 inet dhcp
-      ```
+4. Open the file. You should see the following lines at the end of the file:
 
-   * Keep the existing line item for dhcp as it is. The primary IP address remains configured as it was previously.
-   * Add the following lines after the lines that exist in this file:
+   ```bash
+   auto eth0
+   iface eth0 inet dhcp
+   ```
 
-     ```bash
-     iface eth0 inet static
-     address <your private IP address here> 
-     netmask <your subnet mask> 
-     ```
+5. Add the following lines after the lines that exist in the file. Replace **`10.1.0.5`** with your private IP address and subnet mask.
 
-1. Save the file by using the following command:
+   ```bash
+   iface eth0 inet static
+   address 10.1.0.5
+   netmask 255.255.255.0
+   ```
+    
+    To add additional private IP addresses, edit the file and add the new private IP addresses on subsequent lines:
+
+    ```bash
+    iface eth0 inet static
+    address 10.1.0.5
+    netmask 255.255.255.0
+    iface eth0 inet static
+    address 10.1.0.6
+    netmask 255.255.255.0
+    ```
+
+6. Save the file by using the following command:
 
    ```bash
-   :wq! 
+   :wq
    ```
 
-1. Restart networking services for the changes to take effect. For Debian 8 and above, this can be done using below command :
+7. Restart networking services for the changes to take effect. For Debian 8 and above, this can be done using below command :
 
    ```bash
    systemctl restart networking
@@ -492,29 +510,53 @@ ip route add default via 10.0.0.1 dev eth2 table custom
    service networking restart
    ```
 
-1. Verify that the IP address is added to the network interface with the following command:
+8. Verify the IP address is added to the network interface with the following command:
 
    ```bash
    ip addr list eth0
+   ```
+
+   You should see the IP address you added as part of the list. Example:
+
+    ```bash
+    2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
+    link/ether 00:0d:3a:04:45:16 brd ff:ff:ff:ff:ff:ff
+    inet 10.1.0.5/24 brd 10.1.0.255 scope global eth0
+       valid_lft forever preferred_lft forever
+    inet 10.1.0.6/24 brd 10.1.0.255 scope global secondary eth0
+       valid_lft forever preferred_lft forever
+    inet 10.1.0.4/24 brd 10.1.0.255 scope global secondary eth0
+       valid_lft forever preferred_lft forever
+    inet6 fe80::20d:3aff:fe04:4516/64 scope link
+       valid_lft forever preferred_lft forever
     ```
 
-You should see the IP address you added as part of the list. Example:
+#### Validation (Debian GNU/Linux)
+
+To ensure you're able to connect to the internet from your secondary IP configuration via the public IP associated with it, use the following command:
 
 ```bash
- 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: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
-  link/ether 00:0d:3a:1d:1d:64 brd ff:ff:ff:ff:ff:ff
-  inet 10.2.0.5/24 brd 10.2.0.255 scope global eth0
-     valid_lft forever preferred_lft forever
-  inet 10.2.0.6/24 brd 10.2.0.255 scope global secondary eth0
-     valid_lft forever preferred_lft forever
-  inet6 fe80::20d:3aff:fe1d:1d64/64 scope link
-     valid_lft forever preferred_lft forever
- ```
+ping -I 10.1.0.5 outlook.com
+```
+
+> [!NOTE]
+> For secondary IP configurations, you can only ping to the Internet if the configuration has a public IP address associated with it. For primary IP configurations, a public IP address is not required to ping to the Internet.
+
+For Linux VMs, when attempting to validate outbound connectivity from a secondary NIC, you may need to add appropriate routes. See appropriate documentation for your Linux distribution. The following is one method to accomplish this:
+
+```bash
+echo 150 custom >> /etc/iproute2/rt_tables 
+
+ip rule add from 10.1.0.5 lookup custom
+ip route add default via 10.1.0.1 dev eth2 table custom
+```
+
+- Ensure to replace:
+  
+  - **10.1.0.5** with the private IP address that has a public IP address associated to it
+  
+  - **10.1.0.1** to your default gateway
+  
+  - **eth2** to the name of your secondary NIC
 
 </details>