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Netplan Configuration with VLAN and DHCP Issues

Explore common issues with Netplan configuration for VLANs and DHCP, and learn how to resolve them effectively. --- This video is based on the question https://askubuntu.com/q/1495539/ asked by the user 'averlon' ( https://askubuntu.com/u/487172/ ) and on the answer https://askubuntu.com/a/1495617/ provided by the user 'slangasek' ( https://askubuntu.com/u/25384/ ) at 'Ask Ubuntu' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: netplan with vlan dhcp does not assign address Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to drop me a comment under this video. --- Troubleshooting DHCP Issues with Netplan and VLANs Introduction Configuring network interfaces can sometimes lead to unexpected issues, especially when dealing with VLANs and DHCP assignments. In this post, we will discuss a common problem encountered when configuring Netplan on an Ubuntu device with VLAN and DHCP settings. Our focus will be on resolving issues where the VLAN interface does not receive an IP address as expected. The Problem A user reported a problem with their device setup, which utilizes two physical network interfaces, enp2s0 and enp3s0, to manage VLAN communication. The device runs Ubuntu and hosts a KVM system, requiring the configuration of a bridge. Despite correctly configuring the VLANs in their Netplan configuration file, one of the VLAN interfaces, enp3s0.108, fails to receive an IP address from the DHCP server. The Configuration The user's Netplan configuration includes: [[See Video to Reveal this Text or Code Snippet]] Warning Messages When executing the command netplan status --all, the user received warnings indicating an 'Unknown device type: vlan'. This means that Netplan could not recognize the VLAN configuration due to incorrect setup or underlying issues. The Solution To troubleshoot and resolve the issue with enp3s0.108 failing to receive an IP address, follow these steps: 1. Understand Bridge and IP Configuration When an interface is added to a bridge, you should typically manage the IP configuration through the bridge interface itself. Each interface in a bridge shares the same Layer 3 (L3) configuration, meaning only the bridge should have an IP address. This can simplify management and troubleshooting. 2. Adjust Your Configuration Consider revising your Netplan configuration to ensure that IP configuration is applied to the bridge, not the individual VLANs: Remove IP address assignments from the VLAN interfaces in the configurations. Assign the DHCP settings to the bridge interface br0 instead, which will then manage the IP configuration for the attached VLANs. 3. Test Without Bridge For debugging purposes, you can also test if the VLAN interface can obtain a DHCP address when not included in a bridge configuration. Temporarily disconnect it from the bridge, and apply changes to check if it can acquire an IP address directly. Conclusion Networking configurations can often lead to complex issues, particularly when combining VLANs with bridges and DHCP settings. By understanding the relationship between these elements and adjusting your configuration accordingly, you can effectively resolve IP assignment issues. If you run into more problems, don’t hesitate to reach for community forums or documentation relevant to your specific setup. Happy networking!