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Asked: 2024-09-24T07:41:10+05:30 In:

I’m encountering an issue with my Ubuntu server’s netplan configuration. It seems that there are conflicting default route declarations for IPv4, specifically when I try to set multiple routes. Can someone help me understand how to resolve this issue or what might be causing these conflicts?

I’m trying to set up my Ubuntu server using netplan, and I’ve run into a bit of a roadblock. I’ve got a couple of interfaces to configure and right now, I’m dealing with what appears to be conflicting default route declarations for IPv4. I thought I had everything set up correctly, but it seems like whenever I try to apply the configuration, I’m hit with errors that suggest there are multiple default routes declared.

Here’s a bit of context: I want to set up one interface for my main internet connection and another one for a VPN. The goal is to route all general traffic through the main interface while only routing specific traffic through the VPN. But when I dive into my netplan configuration file, I can’t shake this feeling that I’m missing something. I usually just edit the .yaml file and then run “sudo netplan apply” to see the changes, but it’s not going smoothly this time.

I think the problem might be that both interfaces are trying to declare a default route, but I’m not entirely sure how to specify which one should take precedence or how to set specific routes for the VPN without causing a conflict. I tried commenting out the default route for one of the interfaces, but then nothing seems to work right and I can’t reach the internet at all!

Has anyone experienced something similar or does anyone have insight into netplan’s routing mechanics? How do you properly configure multiple routes without running into conflicts? Also, what configuration details are necessary for defining a specific route for my VPN while keeping my main route intact? I’d appreciate any advice or examples on how to structure the YAML file to avoid these issues. It’s pretty confusing, and I just want to make sure my server runs smoothly! Thanks in advance for any help you can provide.

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    2 Answers



    1. Netplan Configuration Help

      Setting Up Netplan on Ubuntu Server

      Sounds like you’re in a bit of a pickle with your netplan setup! It’s easy to run into issues with routing, especially when dealing with multiple interfaces. Here’s a simple way to think about it:

      Understanding Default Routes

      In your case, you only want one default route for general internet traffic. The VPN should only handle specific traffic, so it’ll need its own routes without taking over the main traffic.

      Basic Configuration Example

      Here’s a basic example of how your YAML configuration could look:

            network:
        version: 2
        ethernets:
          eth0:
            dhcp4: true  # Main internet connection
            routes:
              - to: 0.0.0.0/0       # Default route
                via: 
          eth1:
            addresses: [10.8.0.2/24]  # VPN interface
            routes:
              - to: 0.0.0.0/0        # Do NOT add this line, keep eth0 as the default
                via: 

        # Specify a route for accessing specific services through VPN
        routing-policy:
          - from: 10.8.0.0/24   # VPN network
            table: 100
          - to: /32
            table: 100

      Key Points to Remember

      • Only define the default route for the main interface (eth0 in this case).
      • Do NOT declare a default route in your VPN interface (eth1).
      • Use routing policies if you want specific routes to go through your VPN.

      Applying Changes

      After editing your YAML file, run:

      sudo netplan apply

      Make sure to check the syntax of your YAML file (like indentation) since YAML is sensitive to that!

      Troubleshooting Tips

      If things still don’t work after editing, you can check:

      • Network status: 
        ip route
      • Logs for errors: 
        journalctl -u systemd-networkd

      Hope this helps you clear up the confusion with netplan! Just make sure you get the routes set up right, and you should be all good!




    2. Netplan Configuration for Ubuntu Server

      To resolve the issue of conflicting default routes in your netplan configuration, you need to ensure that only one interface is designated to have a default route while the other is set up to handle specific routes. For example, if you want your Ethernet interface (let’s assume it’s named `eth0`) to be your primary connection and your VPN interface (let’s say it’s `tun0`) to handle specific traffic, you should configure your YAML file such that `eth0` has a default gateway and `tun0` has specific static routes defined for the traffic you want to route through the VPN. The basic structure would look something like this:

      network:
    version: 2
    ethernets:
        eth0:
            dhcp4: true
            addresses: [192.168.1.2/24]
            gateway4: 192.168.1.1
        tun0:
            addresses: [10.8.0.2/24]
            routes:
              - to: 10.0.0.0/24 # Example of a specific route for the VPN
                via: 10.8.0.1 # Assuming this is the VPN gateway

      Additionally, ensure there are no conflicting routes by only specifying the default gateway on `eth0`. After making these changes, run `sudo netplan apply`. If you need to route specific traffic through your VPN without making it the default route, you can further specify routing rules for networks you want directed through `tun0`. If your server is facing connectivity issues after commenting out the route, it’s possible that other configurations might need adjustments, such as DNS settings or firewall rules. To troubleshoot, use `ip route` to view current routing and ensure that the entries correspond to your expected configuration.


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